1
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Chen R, Qiu K, Leong DCY, Kundu BK, Zhang C, Srivastava P, White KE, Li G, Han G, Guo Z, Elles CG, Diao J, Sun Y. A general design of pyridinium-based fluorescent probes for enhancing two-photon microscopy. Biosens Bioelectron 2023; 239:115604. [PMID: 37607448 PMCID: PMC10529004 DOI: 10.1016/j.bios.2023.115604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Revised: 08/04/2023] [Accepted: 08/14/2023] [Indexed: 08/24/2023]
Abstract
Two-photon absorbing fluorescent probes have emerged as powerful imaging tools for subcellular-level monitoring of biological substances and processes, offering advantages such as deep light penetration, minimal photodamage, low autofluorescence, and high spatial resolution. However, existing two-photon absorbing probes still face several limitations, such as small two-photon absorption cross-section, poor water solubility, low membrane permeability, and potentially high toxicity. Herein, we report three small-molecule probes, namely MSP-1arm, Lyso-2arm, and Mito-3arm, composed of a pyridinium center (electron-acceptor) and various methoxystyrene "arms" (electron-donor). These probes exhibit excellent fluorescence quantum yield and decent aqueous solubility. Leveraging the inherent intramolecular charge transfer and excitonic coupling effect, these complexes demonstrate excellent two-photon absorption in the near-infrared region. Notably, Lyso-2arm and Mito-3arm exhibit distinct targeting abilities for lysosomes and mitochondria, respectively. In two-photon microscopy experiments, Mito-3arm outperforms a commercial two-photon absorbing dye in 2D monolayer HeLa cells, delivering enhanced resolution, broader NIR light excitation window, and higher signal-to-noise ratio. Moreover, the two-photon bioimaging of 3D human forebrain organoids confirms the successful deep tissue imaging capabilities of both Lyso-2arm and Mito-3arm. Overall, this work presents a rational design strategy in developing competent two-photon-absorbing probes by varying the number of conjugated "arms" for bioimaging applications.
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Affiliation(s)
- Rui Chen
- Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221, USA
| | - Kangqiang Qiu
- Department of Cancer Biology, College of Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Daniel C Y Leong
- Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221, USA
| | - Bidyut Kumar Kundu
- Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221, USA
| | - Chengying Zhang
- Department of Cancer Biology, College of Medicine, University of Cincinnati, Cincinnati, OH 45267, USA
| | | | - Katie E White
- Department of Chemistry, University of Kansas, Lawrence, KS 66045, USA
| | - Guodong Li
- Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221, USA
| | - Guanqun Han
- Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221, USA
| | - Ziyuan Guo
- Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA
| | | | - Jiajie Diao
- Department of Cancer Biology, College of Medicine, University of Cincinnati, Cincinnati, OH 45267, USA.
| | - Yujie Sun
- Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221, USA.
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2
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Srivastava P, Stierwalt DA, Elles CG. Broadband Two-Photon Absorption Spectroscopy with Stimulated Raman Scattering as an Internal Standard. Anal Chem 2023; 95:13227-13234. [PMID: 37603818 PMCID: PMC10484208 DOI: 10.1021/acs.analchem.3c02298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2023] [Accepted: 08/10/2023] [Indexed: 08/23/2023]
Abstract
Two-photon absorption (2PA) spectroscopy provides valuable information about the nonlinear properties of molecules. In contrast with single-wavelength methods, broadband 2PA spectroscopy using a pump-probe approach gives a continuous 2PA spectrum across a wide range of transition energies without tuning the excitation laser. This contribution shows how stimulated Raman scattering from the solvent can be used as a convenient and robust internal standard for obtaining accurate absolute 2PA cross sections using the broadband approach. Stimulated Raman scattering has the same pump-probe overlap dependence as 2PA, thus eliminating the need to measure the intensity-dependent overlap of the pump and probe directly. Eliminating the overlap represents an important improvement because intensity profiles are typically the largest source of uncertainty in the measurement of absolute 2PA cross sections using any method. Raman scattering cross sections are a fundamental property of the solvent and therefore provide a universal standard that can be applied any time the 2PA and Raman signals are present within the same probe wavelength range. We demonstrate this approach using sample solutions of coumarin 153 in methanol, DMSO, and toluene, as well as fluorescein in water.
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Affiliation(s)
- Prasenjit Srivastava
- Department of Chemistry, University
of Kansas, Lawrence, Kansas 66045, United States
| | - David A. Stierwalt
- Department of Chemistry, University
of Kansas, Lawrence, Kansas 66045, United States
| | - Christopher G. Elles
- Department of Chemistry, University
of Kansas, Lawrence, Kansas 66045, United States
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3
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Singh M, Dhote P, Johnson DR, Figueroa-Lazú S, Elles CG, Boskovic Z. Photochemical Decarbonylation of Oxetanone and Azetidinone: Spectroscopy, Computational Models, and Synthetic Applications. Angew Chem Int Ed Engl 2023; 62:e202215856. [PMID: 36399366 PMCID: PMC9839639 DOI: 10.1002/anie.202215856] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 11/17/2022] [Accepted: 11/18/2022] [Indexed: 11/19/2022]
Abstract
Photoexcitation of cyclic ketones leads to the expulsion of carbon monoxide and a mixture of products derived from diradical intermediates. Here we show that synthetic utility of this process is improved if strained heterocyclic ketones are used. Photochemistry of 3-oxetanone and N-Boc-3-azetidinone has not been previously described. Decarbonylation of these 4-membered rings proceeds through a step-wise Norrish type I cleavage of the C-C bond from the singlet excited state. Ylides derived from both compounds are high-energy species that are kinetically stable long enough to undergo [3+2] cycloaddition with a variety of alkenes and produce substituted tetrahydrofurans and pyrrolidines. The reaction has a sufficiently wide scope to produce scaffolds that were either previously inaccessible or difficult to synthesize, thereby providing experimental access to new chemical space.
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Affiliation(s)
- Manvendra Singh
- Department of Medicinal Chemistry, University of Kansas, Lawrence, 66045 Kansas
| | - Pawan Dhote
- Department of Medicinal Chemistry, University of Kansas, Lawrence, 66045 Kansas
| | - Daniel R. Johnson
- Department of Chemistry, University of Kansas, Lawrence, 66045 Kansas
| | | | | | - Zarko Boskovic
- Department of Medicinal Chemistry, University of Kansas, Lawrence, 66045 Kansas
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4
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Burns KH, Quincy TJ, Elles CG. Excited-state resonance Raman spectroscopy probes the sequential two-photon excitation mechanism of a photochromic molecular switch. J Chem Phys 2022; 157:234302. [PMID: 36550048 DOI: 10.1063/5.0126974] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Some diarylethene molecular switches have a low quantum yield for cycloreversion when excited by a single photon, but react more efficiently following sequential two-photon excitation. The increase in reaction efficiency depends on both the relative time delay and the wavelength of the second photon. This paper examines the wavelength-dependent mechanism for sequential excitation using excited-state resonance Raman spectroscopy to probe the ultrafast (sub-30 fs) dynamics on the upper electronic state following secondary excitation. The approach uses femtosecond stimulated Raman scattering (FSRS) to measure the time-gated, excited-state resonance Raman spectrum in resonance with two different excited-state absorption bands. The relative intensities of the Raman bands reveal the initial dynamics in the higher-lying states, Sn, by providing information on the relative gradients of the potential energy surfaces that are accessed via secondary excitation. The excited-state resonance Raman spectra reveal specific modes that become enhanced depending on the Raman excitation wavelength, 750 or 400 nm. Many of the modes that become enhanced in the 750 nm FSRS spectrum are assigned as vibrational motions localized on the central cyclohexadiene ring. Many of the modes that become enhanced in the 400 nm FSRS spectrum are assigned as motions along the conjugated backbone and peripheral phenyl rings. These observations are consistent with earlier measurements that showed higher efficiency following secondary excitation into the lower excited-state absorption band and illustrate a powerful new way to probe the ultrafast dynamics of higher-lying excited states immediately following sequential two-photon excitation.
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Affiliation(s)
- Kristen H Burns
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, USA
| | - Timothy J Quincy
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, USA
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5
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Singh M, Dhote P, Johnson DR, Figueroa-Lazu S, Elles CG, Boskovic Z. Photochemical Decarbonylation of Oxetanone and Azetidinone: Spectroscopy, Computational Models, and Synthetic Applications. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202215856] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
| | - Pawan Dhote
- University of Kansas Medicinal Chemistry UNITED STATES
| | | | | | | | - Zarko Boskovic
- University of Kansas Medicinal Chemistry 1567 Irving Hill RoadIntegrated Sciences Building 66045 Lawrence UNITED STATES
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6
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Abstract
We prepared a collection of complex cycloheptatriene-containing azetidine lactones by applying two key photochemical reactions: "aza-Yang" cyclization and Buchner carbene insertion into aromatic rings. While photolysis of phenacyl amines leads to a rapid charge transfer and elimination, we found that a simple protonation of the amine enables the formation of azetidinols as single diastereomers. We provide evidence, through ultrafast spectroscopy, for the electron transfer from free amines in the excited state. Further, we characterize the aza-Yang reaction by establishing the dependence of the initial reaction rates on the rates of photon absorption. An unanticipated change in reactivity in morpholine analogues is explained through interactions with the tosylate anion. The Buchner reaction proceeds with a slight preference for one diastereomer over the other, and successful reaction requires electron-donating carbene-stabilizing substituents. Overall, 16 compounds were prepared over seven steps. Guided by an increase in structural complexity, efforts such as this one extend the reach of chemists into unexplored chemical space and provide useful quantities of new compounds for studies focused on their properties.
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Affiliation(s)
- Manvendra Singh
- Department of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Bryce Gaskins
- Department of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Daniel R Johnson
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Christopher G Elles
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Zarko Boskovic
- Department of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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7
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Burns KH, Elles CG. Ultrafast Dynamics of a Molecular Switch from Resonance Raman Spectroscopy: Comparing Visible and UV Excitation. J Phys Chem A 2022; 126:5932-5939. [PMID: 36026439 DOI: 10.1021/acs.jpca.2c05435] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Resonance Raman spectroscopy probes the ultrafast dynamics of a diarylethene (DAE) molecular switch following excitation into the first two optical absorption bands. Mode-specific resonance enhancements for Raman excitation at visible (750-560 nm) and near-UV (420-390 nm) wavelengths compared with the calculated and experimental off-resonance Raman spectrum at 785 nm reveal different Franck-Condon active vibrations for the two electronically excited states. The resonance enhancements at visible wavelengths are consistent with initial motion on the first excited-state that promotes the cycloreversion reaction, whereas the enhancements for excitation at near-UV wavelengths highlight motions involving conjugated backbone and phenyl ring stretching modes that are orthogonal to the reaction coordinate. The results support a mechanism involving rapid internal conversion from the higher-lying state followed by cycloreversion on the first excited state. These observations provide new information about the reactivity of DAE derivatives following excitation in the visible and near-UV.
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Affiliation(s)
- Kristen H Burns
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Christopher G Elles
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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8
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Abstract
This Feature Article highlights the role of spatial confinement in controlling the fundamental behavior of molecules. Select examples illustrate the value of using space as a tool to control and understand excited-state dynamics through a combination of ultrafast spectroscopy and conventional steady-state methods. Molecules of interest were confined within a closed molecular capsule, derived from a cavitand known as octa acid (OA), whose internal void space is sufficient to accommodate molecules as long as tetracene and as wide as pyrene. The free space, i.e., the space that is left following the occupation of the guest within the host, is shown to play a significant role in altering the behavior of guest molecules in the excited state. The results reported here suggest that in addition to weak interactions that are commonly emphasized in supramolecular chemistry, the extent of empty space (i.e., the remaining void space within the capsule) is important in controlling the excited-state behavior of confined molecules on ultrafast time scales. For example, the role of free space in controlling the excited-state dynamics of guest molecules is highlighted by probing the cis-trans isomerization of stilbenes and azobenzenes within the OA capsule. Isomerization of both types of molecule are slowed when they are confined within a small space, with encapsulated azobenzenes taking a different reaction pathway compared to that in solution upon excitation to S2. In addition to steric constraints, confinement of reactive molecules in a small space helps to override the need for diffusion to bring the reactants together, thus enabling the measurement of processes that occur faster than the time scale for diffusion. The advantages of reducing free space and confining reactive molecules are illustrated by recording unprecedented excimer emission from anthracene and by measuring ultrafast electron transfer rates across the organic molecular wall. By monitoring the translational motion of anthracene pairs in a restricted space, it has been possible to document the pathway undertaken by excited anthracene from inception to the formation of the excimer on the excited-state surface. Similarly, ultrafast electron transfer experiments pursued here have established that the process is not hindered by a molecular wall. Apparently, the electron can cross the OA capsule wall provided the donor and acceptor are in close proximity. Measurements on the ultrafast time scale provide crucial insights for each of the examples presented here, emphasizing the value of both "space" and "time" in controlling and understanding the dynamics of excited molecules.
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Affiliation(s)
| | - Pratik Sen
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, UP 208 016, India
| | - Christopher G Elles
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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9
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Bhattacharyya D, Zhang Y, Elles CG, Bradforth SE. Electronic Structure of Liquid Alkanes: A Representative Case of Liquid Hexanes and Cyclohexane Studied Using Polarization-Dependent Two-Photon Absorption Spectroscopy. J Phys Chem A 2021; 125:7988-7999. [PMID: 34478284 DOI: 10.1021/acs.jpca.1c06230] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Two-photon absorption (2PA) spectra of liquid cyclohexane and hexanes are reported for the energy range 6.4-8.5 eV (177-145 nm), providing detailed information about their electronic structures in bulk liquid. Using a broadband pump-probe fashion, we measured the continuous 2PA spectra by simultaneous absorption of a 266 nm (4.6 eV) pump photon and one UV-vis probe photon from the white-light continuum (1.8-3.9 eV). Theoretical one-photon absorption (1PA) and 2PA cross sections of isolated gas phase molecules are computed by the equation of motion coupled-cluster method with single and double substitutions (EOM-CCSD) to substantiate the assignment of the experimental spectra, and the natural transition orbital (NTO) analysis provides visualization of the participating orbitals in a transition. Our analysis suggests that upon solvation transitions at the lowest excitation energy involving promotion of electron to the 3s Rydberg orbitals are blue-shifted (∼0.55 eV for cyclohexane and ∼0.18 eV for hexanes) to a greater extent as compared to those involving other Rydberg orbitals, which is similar to the behavior observed for water and alcohols. All other transitions experience negligible (cyclohexane) or minor red-shift by ∼0.15-0.2 eV (hexane) upon solvation. In both alkanes, the spectra are entirely dominated by Rydberg transitions: the most intense bands in 1PA and 2PA spectra are due to the excitation of electrons to the Rydberg "p" and "d" type orbitals, respectively, although one transition terminating in the 3s Rydberg has significant 2PA strength. This work demonstrates that the gas phase electronic transition properties in alkanes are not significantly altered upon solvation. In addition, electronic structure calculations using an isolated-molecule framework appear to provide a reasonable starting point for a semiquantitative picture for spectral assignment and also to analyze the solvatochromic shifts for liquid phase absorption spectra.
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Affiliation(s)
- Dhritiman Bhattacharyya
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| | - Yuyuan Zhang
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| | - Christopher G Elles
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| | - Stephen E Bradforth
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
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10
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Abstract
Ultrafast transient absorption spectroscopy reveals new excited-state dynamics following excitation of trans-azobenzene (t-Az) and several alkyl-substituted t-Az derivatives encapsulated in a water-soluble supramolecular host-guest complex. Encapsulation increases the excited-state lifetimes and alters the yields of the trans → cis photoisomerization reaction compared with solution. Kinetic modeling of the transient spectra for unsubstituted t-Az following nπ* and ππ* excitation reveals steric trapping of excited-state species, as well as an adiabatic excited-state trans → cis isomerization pathway for confined molecules that is not observed in solution. Analysis of the transient spectra following ππ* excitation for a series of 4-alkyl and 4,4'-dialkyl substituted t-Az molecules suggests that additional crowding due to lengthening of the alkyl tails results in deeper trapping of the excited-state species, including distorted trans and cis structures. The variation of the dynamics due to crowding in the confined environment provides new evidence to explain the violation of Kasha's rule for nπ* and ππ* excitation of azobenzenes based on competition between in-plane inversion and out-of-plane rotation channels.
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Affiliation(s)
| | - A Mohan Raj
- Department of Chemistry, University of Miami Coral Gables Florida USA
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11
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Burns KH, Srivastava P, Elles CG. Absolute Cross Sections of Liquids from Broadband Stimulated Raman Scattering with Femtosecond and Picosecond Pulses. Anal Chem 2020; 92:10686-10692. [PMID: 32598135 DOI: 10.1021/acs.analchem.0c01785] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Broadband stimulated Raman scattering (SRS) is often observed in applications that use nonlinear spectroscopy to probe the composition or dynamics of complex systems. Whether the SRS response is measured intentionally or unintentionally, as a background signal, the relative scattering intensities provide a quantitative measure of the population profile of target molecules. Solvent scattering is a valuable internal reference for determining absolute concentrations in these applications, but accurate cross sections have been reported for only a limited number of transitions in select solvents and were measured using spontaneous Raman scattering with narrowband continuous wave or nanosecond light sources. This work reports the measurement and analysis of absolute Raman scattering cross sections spanning the frequency range of 500-4000 cm-1 for cyclohexane, DMSO, acetonitrile, methanol, water, benzene, and toluene using broadband SRS with femtosecond and picosecond Raman pump pulses at 488 nm. Varying the duration of the Raman pump pulses from ∼80 fs to >1 ps confirms that the cross sections are independent of the spectral bandwidth across the range of ∼250 to <20 cm-1. The cross sections and depolarization ratios measured using broadband SRS agree with the limited number of previously reported values, after accounting for overlapping transitions in the lower-resolution femtosecond and picosecond spectra. The SRS cross sections reported here can be used with confidence as internal reference standards for a wide range of applications, including nonlinear spectroscopy and coherent microscopy measurements using ultrafast lasers.
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Affiliation(s)
- Kristen H Burns
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Prasenjit Srivastava
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Christopher G Elles
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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12
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Barclay MS, Elles CG, Caricato M. On the Discrepancy between Experimental and Calculated Raman Intensities for Conjugated Phenyl and Thiophene Derivatives. J Phys Chem A 2020; 124:4678-4689. [PMID: 32392419 DOI: 10.1021/acs.jpca.0c00363] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Compared with experimental spectra, calculations for conjugated phenyl and thiophene oligomers tend to overestimate the ground state Raman intensities of higher-frequency vibrations (1200-1800 cm-1) relative to the intensities at lower frequencies (<1200 cm-1). The discrepancy was observed in previous benchmarking work that examined the method dependence of the calculated Raman spectra for a series of aromatic molecules. This paper further investigates the nature of the discrepancy by examining the role of anharmonic corrections and the dependence of the calculated Raman spectra on the inter-ring torsion angle for the representative molecules biphenyl (BP), 2-phenylthiophene (PT), and 2,2'-bithiophene (BT). Perturbative anharmonic corrections to the spectra calculated using density functional theory (DFT) provide only slightly better agreement with experiment. On the other hand, calculations at larger torsion angles give up to 30% improvement in the relative Raman intensities compared with the spectra calculated at the optimized geometries. The torsion-angle dependence of the Raman intensities is most pronounced for delocalized C-C and C-S stretching modes, and less pronounced for bending and ring distortion modes that do not involve inter-ring stretching. Higher-level calculations using the coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] method indicate that DFT underestimates the energy barrier for torsion isomerization at small angles, and it overestimates the barriers at large angles, thus predicting minimum geometries at torsion angles that are too small. Therefore, the results suggest that the discrepancy in relative Raman intensities may be related to an overestimation of inter-ring conjugation by DFT, which also tends to favor geometries that are too planar.
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Affiliation(s)
- Matthew S Barclay
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Christopher G Elles
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Marco Caricato
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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13
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Henke WC, Otolski CJ, Moore WNG, Elles CG, Blakemore JD. Ultrafast Spectroscopy of [Mn(CO) 3] Complexes: Tuning the Kinetics of Light-Driven CO Release and Solvent Binding. Inorg Chem 2020; 59:2178-2187. [PMID: 31990533 DOI: 10.1021/acs.inorgchem.9b02758] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Manganese tricarbonyl complexes are promising catalysts for CO2 reduction, but complexes in this family are often photosensitive and decompose rapidly upon exposure to visible light. In this report, synthetic and photochemical studies probe the initial steps of light-driven speciation for Mn(CO)3(Rbpy)Br complexes bearing a range of 4,4'-disubstituted 2,2'-bipyridyl ligands (Rbpy, where R = tBu, H, CF3, NO2). Transient absorption spectroscopy measurements for Mn(CO)3(Rbpy)Br coordination compounds with R = tBu, H, and CF3 in acetonitrile reveal ultrafast loss of a CO ligand on the femtosecond time scale, followed by solvent coordination on the picosecond time scale. The Mn(CO)3(NO2bpy)Br complex is unique among the four compounds in having a longer-lived excited state that does not undergo CO release or subsequent solvent coordination. The kinetics of photolysis and solvent coordination for light-sensitive complexes depend on the electronic properties of the disubstituted bipyridyl ligand. The results indicate that both metal-to-ligand charge-transfer (MLCT) and dissociative ligand-field (d-d) excited states play a role in the ultrafast photochemistry. Taken together, the findings suggest that more robust catalysts could be prepared with appropriately designed complexes that avoid crossing between the excited states that drive photochemical CO loss.
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Affiliation(s)
- Wade C Henke
- Department of Chemistry , University of Kansas , 1567 Irving Hill Road , Lawrence , Kansas 66045-7582 , United States
| | - Christopher J Otolski
- Department of Chemistry , University of Kansas , 1567 Irving Hill Road , Lawrence , Kansas 66045-7582 , United States
| | - William N G Moore
- Department of Chemistry , University of Kansas , 1567 Irving Hill Road , Lawrence , Kansas 66045-7582 , United States
| | - Christopher G Elles
- Department of Chemistry , University of Kansas , 1567 Irving Hill Road , Lawrence , Kansas 66045-7582 , United States
| | - James D Blakemore
- Department of Chemistry , University of Kansas , 1567 Irving Hill Road , Lawrence , Kansas 66045-7582 , United States
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14
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Affiliation(s)
- Matthew S. Barclay
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Christopher G. Elles
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Marco Caricato
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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15
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Barclay MS, Caricato M, Elles CG. Femtosecond Stimulated Raman Scattering from Triplet Electronic States: Experimental and Theoretical Study of Resonance Enhancements. J Phys Chem A 2019; 123:7720-7732. [DOI: 10.1021/acs.jpca.9b05955] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Matthew S. Barclay
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Marco Caricato
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Christopher G. Elles
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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16
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Otolski CJ, Mohan Raj A, Sharma G, Prabhakar R, Ramamurthy V, Elles CG. Ultrafast trans → cis Photoisomerization Dynamics of Alkyl-Substituted Stilbenes in a Supramolecular Capsule. J Phys Chem A 2019; 123:5061-5071. [PMID: 31140802 DOI: 10.1021/acs.jpca.9b03285] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Ultrafast spectroscopy reveals the effects of confinement on the excited-state photoisomerization dynamics for a series of alkyl-substituted trans-stilbenes encapsulated in the hydrophobic cavity of an aqueous supramolecular organic host-guest complex. Compared with the solvated compounds, encapsulated trans-stilbenes have broader excited-state absorption spectra, excited-state lifetimes that are 3-4 times longer, and photoisomerization quantum yields that are 1.7-6.5 times lower in the restricted environment. The organic capsule disrupts the equilibrium structure and restricts torsional rotation around the central C═C double bond in the excited state, which is an important motion for the relaxation of trans-stilbene from S1 to S0. The location and identity of alkyl substituents play a significant role in determining the excited-state dynamics and photoisomerization quantum yields by tuning the relative crowding inside the capsule. The results are discussed in terms of distortions of the ground- and excited-state potential energy surfaces, including the topology of the S1-S0 conical intersection.
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Affiliation(s)
- Christopher J Otolski
- Department of Chemistry , University of Kansas , Lawrence , Kansas 66045 , United States
| | - A Mohan Raj
- Department of Chemistry , University of Miami , Coral Gables , Florida 33146 , United States
| | - Gaurav Sharma
- Department of Chemistry , University of Miami , Coral Gables , Florida 33146 , United States
| | - Rajeev Prabhakar
- Department of Chemistry , University of Miami , Coral Gables , Florida 33146 , United States
| | | | - Christopher G Elles
- Department of Chemistry , University of Kansas , Lawrence , Kansas 66045 , United States
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17
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Bhattacharyya D, Zhang Y, Elles CG, Bradforth SE. Electronic Structure of Liquid Methanol and Ethanol from Polarization-Dependent Two-Photon Absorption Spectroscopy. J Phys Chem A 2019; 123:5789-5804. [DOI: 10.1021/acs.jpca.9b04040] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Dhritiman Bhattacharyya
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| | - Yuyuan Zhang
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| | - Christopher G. Elles
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
| | - Stephen E. Bradforth
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States
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18
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Otolski CJ, Mohan Raj A, Ramamurthy V, Elles CG. Ultrafast Dynamics of Encapsulated Molecules Reveals New Insight on the Photoisomerization Mechanism for Azobenzenes. J Phys Chem Lett 2019; 10:121-127. [PMID: 30563336 DOI: 10.1021/acs.jpclett.8b03070] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Spatial confinement can have a profound impact on the dynamics of chemical reactions, especially for isomerization reactions that involve large-amplitude structural rearrangement of a molecule. This work uses ultrafast spectroscopy to probe the effects of confinement on trans → cis photoisomerization following ππ* excitation of 4-propyl stilbene and 4-propyl azobenzene encapsulated in a supramolecular host-guest complex. Transient absorption spectroscopy of the encapsulated azobenzene derivative reveals the formation of two distinct excited-state species with spectral signatures resembling the cis and trans isomers. Formation of the cis species indicates a direct excited-state isomerization channel that is not observed in cyclohexane solution. Comparison with the stilbene analogue suggests that this "hot" excited-state isomerization pathway for encapsulated azobenzene involves primarily in-plane inversion, whereas a 10-fold increase of the excited-state lifetime for the trans isomer suggests that crowding in the capsule hinders isomerization from the relaxed S1 geometry of the trans isomer. This work provides new mechanistic insight on the relative roles of inversion and rotation in the ultrafast photoisomerization of azobenzene derivatives.
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Affiliation(s)
- Christopher J Otolski
- Department of Chemistry , University of Kansas , Lawrence , Kansas 66045 , United States
| | - A Mohan Raj
- Department of Chemistry , University of Miami , Coral Gables , Florida 33146 , United States
| | | | - Christopher G Elles
- Department of Chemistry , University of Kansas , Lawrence , Kansas 66045 , United States
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19
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Quincy TJ, Barclay MS, Caricato M, Elles CG. Probing Dynamics in Higher-Lying Electronic States with Resonance-Enhanced Femtosecond Stimulated Raman Spectroscopy. J Phys Chem A 2018; 122:8308-8319. [PMID: 30256101 DOI: 10.1021/acs.jpca.8b07855] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Femtosecond stimulated Raman scattering (FSRS) measurements typically probe the structural dynamics of a molecule in the first electronically excited state, S1. While these measurements often rely on an electronic resonance condition to increase signal strength or enhance species selectivity, the effects of the resonance condition are usually neglected. However, mode-specific enhancements of the vibrational transitions in an FSRS spectrum contain detailed information about the resonant (upper) electronic state. Analogous to ground-state resonance Raman spectroscopy, the relative intensities of the Raman bands reveal displacements of the upper potential energy surface due to changes in the bonding pattern upon S n ← S1 electronic excitation, and therefore provide a sensitive probe of the ultrafast dynamics in the higher-lying state, S n. Raman gain profiles from the wavelength-dependent FSRS spectrum of the model compound 2,5-diphenylthiophene (DPT) reveal several modes with large displacement in the upper potential energy surface, including strong enhancement of a delocalized C-S-C stretching and ring deformation mode. The experimental results provide a benchmark for comparison with calculated spectra using time-dependent density functional theory (TD-DFT) and equation-of-motion coupled-cluster theory with single and double excitations (EOM-CCSD), where the calculations are based on the time-dependent formalism for resonance Raman spectroscopy. The simulated spectra are obtained from S1-S n transition strengths and the energy gradients of the upper (S n) potential energy surfaces along the S1 normal mode coordinates. The experimental results provide a stringent test of the computational approach, and indicate important limitations based on the level of theory and basis set. This work provides a foundation for making more accurate assignments of resonance-enhanced excited-state Raman spectra, as well as extracting novel information about higher-lying excited states in the transient absorption spectrum of a molecule.
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Affiliation(s)
- Timothy J Quincy
- Department of Chemistry , University of Kansas , Lawrence , Kansas 66045 , United States
| | - Matthew S Barclay
- Department of Chemistry , University of Kansas , Lawrence , Kansas 66045 , United States
| | - Marco Caricato
- Department of Chemistry , University of Kansas , Lawrence , Kansas 66045 , United States
| | - Christopher G Elles
- Department of Chemistry , University of Kansas , Lawrence , Kansas 66045 , United States
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20
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de Wergifosse M, Houk AL, Krylov AI, Elles CG. Two-photon absorption spectroscopy of trans-stilbene, cis-stilbene, and phenanthrene: Theory and experiment. J Chem Phys 2018; 146:144305. [PMID: 28411609 DOI: 10.1063/1.4979651] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Two-photon absorption (2PA) spectroscopy provides complementary, and sometimes more detailed, information about the electronic structure of a molecule relative to one-photon absorption (1PA) spectroscopy. However, our understanding of the 2PA processes is rather limited due to technical difficulties in measuring experimental 2PA spectra and theoretical challenges in computing higher-order molecular properties. This paper examines the 2PA spectroscopy of trans-stilbene, cis-stilbene, and phenanthrene by a combined experimental and theoretical approach. The broadband 2PA spectra of all three compounds are measured under identical conditions in order to facilitate a direct comparison of the absolute 2PA cross sections in the range 3.5-6.0 eV. For comparison, the theoretical 2PA cross sections are computed using the equation-of-motion coupled-cluster method with single and double substitutions. Simulated 2PA spectra based on the calculations reproduce the main features of the experimental spectra in solution, although the quantitative comparison is complicated by a number of uncertainties, including limitations of the theoretical model, vibronic structure, broadening of the experimental spectra, and solvent effects. The systematic comparison of experimental and theoretical spectra for this series of structurally similar compounds provides valuable insight into the nature of 2PA transitions in conjugated molecules. Notably, the orbital character and symmetry-based selection rules provide a foundation for interpreting the features of the experimental 2PA spectra in unprecedented detail.
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Affiliation(s)
- Marc de Wergifosse
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, USA
| | - Amanda L Houk
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, USA
| | - Anna I Krylov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, USA
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21
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Barclay MS, Quincy TJ, Williams-Young DB, Caricato M, Elles CG. Accurate Assignments of Excited-State Resonance Raman Spectra: A Benchmark Study Combining Experiment and Theory. J Phys Chem A 2017; 121:7937-7946. [DOI: 10.1021/acs.jpca.7b09467] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Matthew S. Barclay
- Department
of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Timothy J. Quincy
- Department
of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | | | - Marco Caricato
- Department
of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Christopher G. Elles
- Department
of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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22
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de Wergifosse M, Elles CG, Krylov AI. Two-photon absorption spectroscopy of stilbene and phenanthrene: Excited-state analysis and comparison with ethylene and toluene. J Chem Phys 2017; 146:174102. [DOI: 10.1063/1.4982045] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Marc de Wergifosse
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, USA
| | | | - Anna I. Krylov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, USA
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23
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Batignani G, Pontecorvo E, Ferrante C, Aschi M, Elles CG, Scopigno T. Visualizing Excited-State Dynamics of a Diaryl Thiophene: Femtosecond Stimulated Raman Scattering as a Probe of Conjugated Molecules. J Phys Chem Lett 2016; 7:2981-8. [PMID: 27428853 DOI: 10.1021/acs.jpclett.6b01137] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Conjugated organic polymers based on substituted thiophene units are versatile building blocks of many photoactive materials, such as photochromic molecular switches or solar energy conversion devices. Unraveling the different processes underlying their photochemistry, such as the evolution on different electronic states and multidimensional structural relaxation, is a challenge critical to defining their function. Using femtosecond stimulated Raman scattering (FSRS) supported by quantum chemical calculations, we visualize the reaction pathway upon photoexcitation of the model compound 2-methyl-5-phenylthiophene. Specifically, we find that the initial wavepacket dynamics of the reaction coordinates occurs within the first ≈1.5 ps, followed by a ≈10 ps thermalization. Subsequent slow opening of the thiophene ring through a cleavage of the carbon-sulfur bond triggers an intersystem crossing to the triplet excited state. Our work demonstrates how a detailed mapping of the excited-state dynamics can be obtained, combining simultaneous structural sensitivity and ultrafast temporal resolution of FSRS with the chemical information provided by time-dependent density functional theory calculations.
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Affiliation(s)
- Giovanni Batignani
- Dipartimento di Fisica, Universitá di Roma "La Sapienza" , Roma I-00185, Italy
- Dipartimento di Scienze Fisiche e Chimiche, Universitá degli Studi dell'Aquila , L'Aquila I-67100, Italy
| | - Emanuele Pontecorvo
- Dipartimento di Fisica, Universitá di Roma "La Sapienza" , Roma I-00185, Italy
| | - Carino Ferrante
- Dipartimento di Fisica, Universitá di Roma "La Sapienza" , Roma I-00185, Italy
| | - Massimiliano Aschi
- Dipartimento di Scienze Fisiche e Chimiche, Universitá degli Studi dell'Aquila , L'Aquila I-67100, Italy
| | - Christopher G Elles
- Department of Chemistry, University of Kansas , Lawrence, Kansas 66045, United States
| | - Tullio Scopigno
- Dipartimento di Fisica, Universitá di Roma "La Sapienza" , Roma I-00185, Italy
- Center for Life Nano Science @Sapienza, Istituto Italiano di Tecnologia , Roma I-00161, Italy
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24
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Houk AL, Givens RS, Elles CG. Two-Photon Activation of p-Hydroxyphenacyl Phototriggers: Toward Spatially Controlled Release of Diethyl Phosphate and ATP. J Phys Chem B 2016; 120:3178-86. [PMID: 26962676 DOI: 10.1021/acs.jpcb.5b12150] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Two-photon activation of the p-hydroxyphenacyl (pHP) photoactivated protecting group is demonstrated for the first time using visible light at 550 nm from a pulsed laser. Broadband two-photon absorption measurements reveal a strong two-photon transition (>10 GM) near 4.5 eV that closely resembles the lowest-energy band at the same total excitation energy in the one-photon absorption spectrum of the pHP chromophore. The polarization dependence of the two-photon absorption band is consistent with excitation to the same S3 ((1)ππ*) excited state for both one- and two-photon activation. Monitoring the progress of the uncaging reaction under nonresonant excitation at 550 nm confirms a quadratic intensity dependence and that two-photon activation of the uncaging reaction is possible using visible light in the range 500-620 nm. Deprotonation of the pHP chromophore under mildly basic conditions shifts the absorption band to lower energy (3.8 eV) in both the one- and two-photon absorption spectra, suggesting that two-photon activation of the pHP chromophore may be possible using light in the range 550-720 nm. The results of these measurements open the possibility of spatially and temporally selective release of biologically active compounds from the pHP protecting group using visible light from a pulsed laser.
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Affiliation(s)
- Amanda L Houk
- Department of Chemistry, University of Kansas , Lawrence, Kansas 66045, United States
| | - Richard S Givens
- Department of Chemistry, University of Kansas , Lawrence, Kansas 66045, United States
| | - Christopher G Elles
- Department of Chemistry, University of Kansas , Lawrence, Kansas 66045, United States
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25
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Langdon B, Garlick J, Ren X, Wilson DJ, Summers AM, Zigo S, Kling MF, Lei S, Elles CG, Wells E, Poliakoff ED, Carnes KD, Kumarappan V, Ben-Itzhak I, Trallero-Herrero CA. Carrier-envelope-phase stabilized terawatt class laser at 1 kHz with a wavelength tunable option. Opt Express 2015; 23:4563-4572. [PMID: 25836493 DOI: 10.1364/oe.23.004563] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We demonstrate a chirped-pulse-amplified Ti:Sapphire laser system operating at 1 kHz, with 20 mJ pulse energy, 26 femtosecond pulse duration (0.77 terawatt), and excellent long term carrier-envelope-phase (CEP) stability. A new vibrational damping technique is implemented to significantly reduce vibrational noise on both the laser stretcher and compressor, thus enabling a single-shot CEP noise value of 250 mrad RMS over 1 hour and 300 mrad RMS over 9 hours. This is, to the best of our knowledge, the best long term CEP noise ever reported for any terawatt class laser. This laser is also used to pump a white-light-seeded optical parametric amplifier, producing 6 mJ of total energy in the signal and idler with 18 mJ of pumping energy. Due to preservation of the CEP in the white-light generated signal and passive CEP stability in the idler, this laser system promises synthesized laser pulses spanning multi-octaves of bandwidth at an unprecedented energy scale.
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26
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Houk AL, Zheldakov IL, Tommey TA, Elles CG. Two-Photon Excitation of trans-Stilbene: Spectroscopy and Dynamics of Electronically Excited States above S1. J Phys Chem B 2014; 119:9335-44. [DOI: 10.1021/jp509959n] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Amanda L. Houk
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Igor L. Zheldakov
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Tyler A. Tommey
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Christopher G. Elles
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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27
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Ward CL, Elles CG. Cycloreversion dynamics of a photochromic molecular switch via one-photon and sequential two-photon excitation. J Phys Chem A 2014; 118:10011-9. [PMID: 25310194 DOI: 10.1021/jp5088948] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ultrafast pump-probe (PP) and pump-repump-probe (PReP) measurements examine the ring-opening reaction of a photochromic molecular switch following excitation to the first and higher excited states. Sequential two-photon excitation is a sensitive probe of the excited-state dynamics, because the secondary excitation maps the progress along the S1 reaction coordinate onto the higher excited states of the molecule. In this contribution, secondary excitation at 800 nm accesses more reactive regions of the excited-state potential energy surfaces than are accessible with direct vertical excitation in the visible or UV. The quantum yield for cycloreversion increases by a factor of 3.5 ± 0.9 compared with one-photon excitation when the delay between the 500 nm pump and 800 nm repump laser pulses increases beyond ~100 fs, in contrast with a slower ~3 ps increase that was previously observed for one-color sequential excitation at 500 nm. The evolution of an excited-state absorption band reveals the dynamics of the higher-lying excited state for both one-photon excitation in the UV and sequential two-photon excitation. The spectroscopy and dynamics of the higher-lying excited state are similar for both excitation pathways, including a lifetime of ~100 fs. The complementary PP and PReP measurements provide a detailed picture of the ultrafast excited-state dynamics, including new insight on the role of excited states above S1 in controlling the photochemical cycloreversion reaction.
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Affiliation(s)
- Cassandra L Ward
- Department of Chemistry, University of Kansas , Lawrence, Kansas 66045, United States
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28
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Pontecorvo E, Ferrante C, Elles CG, Scopigno T. Structural Rearrangement Accompanying the Ultrafast Electrocyclization Reaction of a Photochromic Molecular Switch. J Phys Chem B 2014; 118:6915-21. [DOI: 10.1021/jp5051047] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Emanuele Pontecorvo
- Dipartimento
di Fisica, Università di Roma “Sapienza”, P.le Aldo Moro 2, I-00185 Roma, Italy
| | - Carino Ferrante
- Dipartimento
di Fisica, Università di Roma “Sapienza”, P.le Aldo Moro 2, I-00185 Roma, Italy
| | - Christopher G. Elles
- Department
of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Tullio Scopigno
- Dipartimento
di Fisica, Università di Roma “Sapienza”, P.le Aldo Moro 2, I-00185 Roma, Italy
- Centre
for Life Nano Science IIT@Sapienza, Istituto Italiano di Tecnologia, I-00161 Roma, Italy
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29
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Zheldakov IL, Grinevich O, Mejiritski A, Elles CG, Neckers DC. Transient Spectroscopy of 5,7-diiodo-3-butoxy-6-fluorone (DIBF). Photochem Photobiol 2013. [DOI: 10.1111/php.12190] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Igor L. Zheldakov
- Department of Chemistry; University of Kansas; Lawrence KS
- Spectra Group Limited; Inc.; Millbury OH
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30
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Pontecorvo E, Ferrante C, Elles CG, Scopigno T. Spectrally tailored narrowband pulses for femtosecond stimulated Raman spectroscopy in the range 330-750 nm. Opt Express 2013; 21:6866-72. [PMID: 23546068 DOI: 10.1364/oe.21.006866] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Spectral compression of femtosecond pulses by second harmonic generation in the presence of substantial group velocity dispersion provides a convenient source of narrowband Raman pump pulses for femtosecond stimulated Raman spectroscopy (FSRS). We discuss here a simple and efficient modification that dramatically increases the versatility of the second harmonic spectral compression technique. Adding a spectral filter following second harmonic generation produces narrowband pulses with a superior temporal profile. This simple modification i) increases the Raman gain for a given pulse energy, ii) improves the spectral resolution, iii) suppresses coherent oscillations associated with slowly dephasing vibrations, and iv) extends the useful tunable range to at least 330-750 nm.
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Affiliation(s)
- E Pontecorvo
- Dipartimento di Fisica, Universita' Roma Sapienza, P.le Aldo Moro 2, Rome, Italy
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31
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Ward CL, Elles CG. Controlling the Excited-State Reaction Dynamics of a Photochromic Molecular Switch with Sequential Two-Photon Excitation. J Phys Chem Lett 2012; 3:2995-3000. [PMID: 26292240 DOI: 10.1021/jz301330z] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Sequential two-photon excitation increases the cycloreversion yield of a diarylethene-type photochromic molecular switch compared with one-photon excitation. This letter shows for the first time that an optimal delay of ∼5 ps between primary and secondary excitation events gives the largest enhancement of the ring-closing reaction. Pump-probe (PP) and pump-repump-probe (PReP) measurements also provide detailed new information about the excited-state dynamics. The initially excited molecule must first cross a barrier on the excited-state potential energy surface before secondary excitation enhances the reaction. The PReP experiments demonstrate that the reaction path of a photochromic molecular switch can be selectively controlled through judicious use of time-delayed femtosecond laser pulses.
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Affiliation(s)
- Cassandra L Ward
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Christopher G Elles
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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32
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Marsalek O, Elles CG, Pieniazek PA, Pluhařová E, VandeVondele J, Bradforth SE, Jungwirth P. Chasing charge localization and chemical reactivity following photoionization in liquid water. J Chem Phys 2012; 135:224510. [PMID: 22168706 DOI: 10.1063/1.3664746] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy. This is one of the fastest fundamental processes occurring in radiation-induced chemistry in aqueous systems and biological tissue. However, unlike the excess electron formed in the same process, the nature and time evolution of the cationic hole has been hitherto little studied. Simulations show that an initially partially delocalized cationic hole localizes within ~30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately, leading to the formation of the OH radical and the hydronium cation in a reaction which can be formally written as H(2)O(+) + H(2)O → OH + H(3)O(+). The exact amount of initial spin delocalization is, however, somewhat method dependent, being realistically described by approximate density functional theory methods corrected for the self-interaction error. Localization, and then the evolving separation of spin and charge, changes the electronic structure of the radical center. This is manifested in the spectrum of electronic excitations which is calculated for the ensemble of ab initio molecular dynamics trajectories using a quantum mechanics/molecular mechanics (QM∕MM) formalism applying the equation of motion coupled-clusters method to the radical core. A clear spectroscopic signature is predicted by the theoretical model: as the hole transforms into a hydroxyl radical, a transient electronic absorption in the visible shifts to the blue, growing toward the near ultraviolet. Experimental evidence for this primary radiation-induced process is sought using femtosecond photoionization of liquid water excited with two photons at 11 eV. Transient absorption measurements carried out with ~40 fs time resolution and broadband spectral probing across the near-UV and visible are presented and direct comparisons with the theoretical simulations are made. Within the sensitivity and time resolution of the current measurement, a matching spectral signature is not detected. This result is used to place an upper limit on the absorption strength and/or lifetime of the localized H(2)O(+) ((aq)) species.
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Affiliation(s)
- Ondrej Marsalek
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic
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33
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Zheldakov IL, Wasylenko JM, Elles CG. Excited-state dynamics and efficient triplet formation in phenylthiophene compounds. Phys Chem Chem Phys 2012; 14:6211-8. [DOI: 10.1039/c2cp23602h] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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34
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Elles CG, Rivera CA, Zhang Y, Pieniazek PA, Bradforth SE. Electronic structure of liquid water from polarization-dependent two-photon absorption spectroscopy. J Chem Phys 2009; 130:084501. [DOI: 10.1063/1.3078336] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
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35
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Elles CG, Shkrob IA, Crowell RA, Arms DA, Landahl EC. Transient x-ray absorption spectroscopy of hydrated halogen atom. J Chem Phys 2008; 128:061102. [DOI: 10.1063/1.2827456] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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36
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Elles CG, Shkrob IA, Crowell RA, Bradforth SE. Excited state dynamics of liquid water: Insight from the dissociation reaction following two-photon excitation. J Chem Phys 2007; 126:164503. [PMID: 17477610 DOI: 10.1063/1.2727468] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The authors use transient absorption spectroscopy to monitor the ionization and dissociation products following two-photon excitation of pure liquid water. The primary decay mechanism changes from dissociation at an excitation energy of 8.3 eV to ionization at 12.4 eV. The two channels occur with similar yield for an excitation energy of 9.3 eV. For the lowest excitation energy, the transient absorption at 267 nm probes the geminate recombination kinetics of the H and OH fragments, providing a window on the dissociation dynamics. Modeling the OH geminate recombination indicates that the dissociating H atoms have enough kinetic energy to escape the solvent cage and one or two additional solvent shells. The average initial separation of H and OH fragments is 0.7+/-0.2 nm. Our observation suggests that the hydrogen bonding environment does not prevent direct dissociation of an O-H bond in the excited state. We discuss the implications of our measurement for the excited state dynamics of liquid water and explore the role of those dynamics in the ionization mechanism at low excitation energies.
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Affiliation(s)
- Christopher G Elles
- Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
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Elles CG, Jailaubekov AE, Crowell RA, Bradforth SE. Excitation-energy dependence of the mechanism for two-photon ionization of liquid H2O and D2O from 8.3to12.4eV. J Chem Phys 2006; 125:44515. [PMID: 16942164 DOI: 10.1063/1.2217738] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Transient absorption measurements monitor the geminate recombination kinetics of solvated electrons following two-photon ionization of liquid water at several excitation energies in the range from 8.3 to 12.4 eV. Modeling the kinetics of the electron reveals its average ejection length from the hydronium ion and hydroxyl radical counterparts and thus provides insight into the ionization mechanism. The electron ejection length increases monotonically from roughly 0.9 nm at 8.3 eV to nearly 4 nm at 12.4 eV, with the increase taking place most rapidly above 9.5 eV. We connect our results with recent advances in the understanding of the electronic structure of liquid water and discuss the nature of the ionization mechanism as a function of excitation energy. The isotope dependence of the electron ejection length provides additional information about the ionization mechanism. The electron ejection length has a similar energy dependence for two-photon ionization of liquid D(2)O, but is consistently shorter than in H(2)O by about 0.3 nm across the wide range of excitation energies studied.
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Affiliation(s)
- Christopher G Elles
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
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Abstract
▪ Abstract Modern ultrafast spectroscopic techniques provide new opportunities to study chemical reaction dynamics in liquids and hold the possibility of obtaining much of the same detailed information available in gases. Vibrational energy transfer studies are the most advanced of the investigations and demonstrate that it is possible to observe state-specific pathways of energy flow within a vibrationally excited molecule (intramolecular vibrational relaxation) and into the surrounding solvent molecules (intermolecular energy transfer). Energy transfer in liquids and gases share many common aspects, but the presence of the solvent also alters the relaxation in both obvious and subtle ways. Photodissociation is amenable to similarly detailed study in liquids, and there are informative new measurements. Bimolecular reactions have received the least attention in state-resolved measurements in liquids, but the means to carry them much further now exist. Studying photodissociation and bimolecular reaction of molecules prepared with initial vibrational excitation in liquids is a realistic, but challenging, goal.
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Affiliation(s)
- Christopher G Elles
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
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Sheps L, Crowther AC, Elles CG, Crim FF. Recombination Dynamics and Hydrogen Abstraction Reactions of Chlorine Radicals in Solution. J Phys Chem A 2005; 109:4296-302. [PMID: 16833759 DOI: 10.1021/jp051072l] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We observe chlorine radical dynamics in solution following two-photon photolysis of the solvent, dichloromethane. In neat CH(2)Cl(2), one-third of the chlorine radicals undergo diffusive geminate recombination, and the rest abstract a hydrogen atom from the solvent with a bimolecular rate constant of (1.35 +/- 0.06) x 10(7) M(-1) s(-1). Upon addition of hydrogen-containing solutes, the chlorine atom decay becomes faster, reflecting the presence of a new reaction pathway. We study 16 different solutes that include alkanes (pentane, hexane, heptane, and their cyclic analogues), alcohols (methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol), and chlorinated alkanes (cyclohexyl chloride, 1-chlorobutane, 2-chlorobutane, 1,2-dichlorobutane, and 1,4-dichlorobutane). Chlorine reactions with alkanes have diffusion-limited rate constants that do not depend on the molecular structure, indicating the absence of a potential barrier. Hydrogen abstraction from alcohols is slower than from alkanes and depends weakly on molecular structure, consistent with a small reaction barrier. Reactions with chlorinated alkanes are the slowest, and their rate constants depend strongly on the number and position of the chlorine substituents, signaling the importance of activation barriers to these reactions. The relative rate constants for the activation-controlled reactions agree very well with the predictions of the gas-phase structure-activity relationships.
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Affiliation(s)
- Leonid Sheps
- Department of Chemistry, University of Wisconsin, Madison, WI 53706, USA
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Affiliation(s)
- Christopher G. Elles
- Department of Chemistry, University of Wisconsin − Madison, Madison, Wisconsin 53706
| | - M. Jocelyn Cox
- Department of Chemistry, University of Wisconsin − Madison, Madison, Wisconsin 53706
| | - George L. Barnes
- Department of Chemistry, University of Wisconsin − Madison, Madison, Wisconsin 53706
| | - F. Fleming Crim
- Department of Chemistry, University of Wisconsin − Madison, Madison, Wisconsin 53706
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Abstract
Transient electronic absorption measurements reveal the vibrational relaxation dynamics of CH(3)I following excitation of the C-H stretch overtone in the gas phase and in liquid solutions. The isolated molecule relaxes through two stages of intramolecular vibrational relaxation (IVR), a fast component that occurs in a few picoseconds and a slow component that takes place in about 400 ps. In contrast, a single 5-7 ps component of IVR precedes intermolecular energy transfer (IET) to the solvent, which dissipates energy from the molecule in 50 ps, 44 ps, and 16 ps for 1 M solutions of CH(3)I in CCl(4), CDCl(3), and (CD(3))(2)CO, respectively. The vibrational state structure suggests a model for the relaxation dynamics in which a fast component of IVR populates the states that are most strongly coupled to the initially excited C-H stretch overtone, regardless of the environment, and the remaining, weakly coupled states result in a secondary relaxation only in the absence of IET.
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Affiliation(s)
- Christopher G Elles
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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