1
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Wang Y, Ye Z, Han T, Du Y, Xue J. Transient spectroscopic insights into nitroindole's T 1 state: Elucidating its intermediates and unique photochemical properties. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2024; 319:124555. [PMID: 38823242 DOI: 10.1016/j.saa.2024.124555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2024] [Revised: 05/25/2024] [Accepted: 05/28/2024] [Indexed: 06/03/2024]
Abstract
Indoles are notable for their distinct photophysical and photochemical properties, making them useful indicators in biological systems and promising candidates for a variety of pharmaceutical applications. While some indoles exhibit room temperature phosphorescence, such a phenomenon has not been observed in nitroindoles. Typically, adding of a nitro group into aromatic compounds promotes ultrafast intersystem crossing and increases the formation quantum yield of the lowest excited triplet (T1). Therefore, understanding the reactivity of nitroindoles' T1 states is imperative. This study investigated the physical properties and chemical reactivities of the T1 state of 6-nitroindole (3HN-6NO2) in both polar aprotic and protic solvents, using transient absorption spectroscopy. Our results demonstrate the basicity and acidity of 3HN-6NO2, emphasizing its potential for protonation and dissociation in mildly acidic and basic conditions, respectively. Furthermore, 3HN-6NO2 has a high oxidizing capacity, participating in electron transfer reactions and proton-coupled electron transfer to produce radicals. Interestingly, in protic solvents like alcohols, 3HN-6NO2 dissociates at the -NH group and forms N-H…O hydrogen-bonded complexes with the nitro group. By identifying transient absorption spectra of intermediates and quantifying kinetic reaction rate constants, we illuminate the unique properties of the T1 state nitroindoles, enriching our understanding of their photophysical and photochemical behaviors. The results of this study have significant implications for their potential application in both biological systems and materials science.
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Affiliation(s)
- Yangxin Wang
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials, Zhejiang Sci-Tech University, Hangzhou 310018, China
| | - Zhao Ye
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials, Zhejiang Sci-Tech University, Hangzhou 310018, China
| | - Ting Han
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials, Zhejiang Sci-Tech University, Hangzhou 310018, China
| | - Yong Du
- Centre for THz Research, China Jiliang University, Hangzhou, 310018, China
| | - Jiadan Xue
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials, Zhejiang Sci-Tech University, Hangzhou 310018, China.
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2
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Hunt JR, Hecht J, Goolsby C, Hagihara J, Loza M, del Pozo S. Excited State Proton Transfer from Acidic Alcohols to a Quinoline Photobase Can Be Solvated by Non-Acidic Alcohol Solvents. J Phys Chem A 2024; 128:6199-6207. [PMID: 39034730 PMCID: PMC11299183 DOI: 10.1021/acs.jpca.4c02907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2024] [Revised: 06/25/2024] [Accepted: 07/11/2024] [Indexed: 07/23/2024]
Abstract
Photobases are a type of molecule that become more basic upon photoexcitation and can therefore be used to control proton transfer reactions with light. The solvation requirements for excited state proton transfer (ESPT) in photobase systems is poorly understood, which limits their applicability. Here, we investigate the solvation of the ESPT reaction using 5-methoxyquinoline (MeOQ), a well-studied photobase with an excited state pKa (pKa*) of approximately 15.1, as a model system. Previous studies have shown that, in addition to the acidic donor that donates a proton to the photoexcited MeOQ, an additional "auxiliary donor" is necessary to solvate the resulting alkoxide. We investigate whether a nonacidic hydrogen bond donor (an alcohol solvent that MeOQ cannot deprotonate in bulk) can act as the auxiliary donor for the MeOQ ESPT reaction. First, we use steady state spectroscopy, TCSPC, and electronic structure calculations to show that MeOQ can deprotonate the acidic donor 2,2,2-trifluoroethanol (TFE, pKa = 12.5) using ethanol as the auxiliary donor. We show that the degree of ESPT is largely predicted by the degree of ground state hydrogen bonding between the photobase and the acidic donor. Next, we study the deprotonation of the acidic donors TFE and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP, pKa = 9.3) with MeOQ in a variety of nonacidic alcohol solvents of varying chain length and branching. MeOQ ESPT occurs to varying extents in all solvents, suggesting that all studied nonacidic alcohols can function as auxiliary donors. We show that the concentration of the acidic donor is strongly correlated with the degree of ESPT. These results are necessary fundamental steps toward the understanding of the photobase ESPT reaction and its wide application in a variety of chemical systems.
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Affiliation(s)
- Jonathan Ryan Hunt
- Loyola Marymount University, Los Angeles, California 90045, United States
| | - Joseph Hecht
- Loyola Marymount University, Los Angeles, California 90045, United States
| | - Clara Goolsby
- Loyola Marymount University, Los Angeles, California 90045, United States
| | - Jade Hagihara
- Loyola Marymount University, Los Angeles, California 90045, United States
| | - Monique Loza
- Loyola Marymount University, Los Angeles, California 90045, United States
| | - Samantha del Pozo
- Loyola Marymount University, Los Angeles, California 90045, United States
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3
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Mathew R, Verma P, Barak A, Adithya Lakshmanna Y. Excited-State Dynamics in 4-[4'(Dimethylamino)styryl]pyridine, a Photobase: Role of Photoinitiated Proton-Coupled Electron Transfer. J Phys Chem A 2023; 127:7419-7428. [PMID: 37647516 DOI: 10.1021/acs.jpca.3c02502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
Abstract
The photoinitiated proton-coupled electron transfer (PCET) process in photoacid-based adducts is predominantly governed by the evolution of the electron-proton transfer state. However, such a process is underexplored in the case of photobases as the excited states evolve through multiple competitive channels. Here, we elucidate the excited-state dynamics of a photobase, 4-[4'-(dimethylamino)styryl]pyridine (DMASP), in the presence of hexafluoroisopropanol (HFIP) that enables PCET. Transient absorption measurements show the evolution of a protonated species in the excited state with a time constant of ∼2.5 ps. Fluorescence upconversion measurements reveal the signatures of an emissive intramolecular charge transfer state and a protonated state. The role of such states is further confirmed by time-resolved measurements in the presence of trifluoroacetic acid and computational analysis. Furthermore, the proton-abstraction dynamics of DMASP is analyzed in bulk methanol and butanol solvents. The extent of proton abstraction by DMASP is found to be higher in the presence of HFIP when compared with the normal alcohols over a time period of a few picoseconds.
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Affiliation(s)
- Reshma Mathew
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Vithura, Thiruvananthapuram 695551, India
| | - Preetika Verma
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Vithura, Thiruvananthapuram 695551, India
| | - Arvind Barak
- Department of Inorganic and Physical Chemistry, Indian Institute of Science Bangalore, Bangalore 560012, India
| | - Yapamanu Adithya Lakshmanna
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Vithura, Thiruvananthapuram 695551, India
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4
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Wu Y, Wang Y, Guan H, Du Y, Zheng X, Xue J. Effect of electron-donating substitution on the triplet state reactivities of 1-nitronaphthalene. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023; 286:121997. [PMID: 36308824 DOI: 10.1016/j.saa.2022.121997] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 09/23/2022] [Accepted: 10/13/2022] [Indexed: 06/16/2023]
Abstract
Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs), often found in polluted air, are carcinogenic and mutagenic. The nitro group increases the spin-orbit coupling and results in the lowest excited triplet (T1) on the picosecond time scale with a high yield. The electron-donating substituents have a significant influence on the photophysics and photochemistry of nitro-PAHs. We used transient absorption spectroscopy and kinetic analysis to investigate the reactivities of the T1 state 1-methoxy-4-nitronaphthalene (3MeO-NN) and 1-methyl-4-nitronaphthalene (3Me-NN). The results show that the methoxy and methyl substitutions have a minor effect on their hydrogen abstraction and electron accepting abilities. The main distinction is their reaction rates towards protons. The second order rate constant of 3MeO-NN towards protons is three orders of magnitude greater than that of 3Me-NN, indicating that 3MeO-NN has a stronger hydrogen bond accepting ability. The kinetic analysis reveals that the dimer of 2,2,2-trifluoroethanol participates in the reaction with 3MeO-NN. These results suggest that the formation of the hydrogen-bonded complex is responsible for the unusually short lifetime of 3MeO-NN in methanol solution and the lack of hydrogen abstraction radicals during the decay of 3MeO-NN in methanol.
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Affiliation(s)
- Yu Wu
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, China
| | - Yangxin Wang
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, China
| | - Huaiyu Guan
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, China
| | - Yong Du
- Centre for THz Research, Jiliang University, Hangzhou 310018, China
| | - Xuming Zheng
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, China
| | - Jiadan Xue
- Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, China; Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou 310018, China.
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5
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Abstract
Dative bonding or Lewis acid-base chemistry underpins a large number of chemical phenomena in a variety of fields, such as catalysis, metal-ligand interactions, and surface chemistry. Developing light-controlled Lewis acid-base interactions could offer a new way of controlling and understanding such phenomena. Photoinduced proton transfer, that is, excited-state Brønsted acidity and basicity, has been extensively studied and applied. Here, in direct analogy to excited-state Brønsted basicity, we show that exciting a photobasic molecule with light generates a thermodynamic drive for the transfer of a Lewis acid from a donor to a photobasic molecule. We have used the archetypal BF3 as our Lewis acid and our photoactive Lewis bases are a family of quinolines, which are known Brønsted photobases as well. We have constructed the experimental Förster cycle for this system and have verified it computationally to demonstrate that a significant drive (0.2-0.7 eV) exists for the transfer of BF3 to a photoexcited quinoline. The magnitude of this drive is similar to those reported for Brønsted photobasicity in quinolines. Computational results from TDDFT and energy decomposition analysis show that the origin of such an effect is similar to the Brønsted photoactivity of these molecules, in that they follow the Hammett parameter of substituent groups. These results suggest that photobases may be capable of controlling the chemical phenomena beyond proton transfer and may open opportunities for a new handle in photocatalysis.
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Affiliation(s)
- Matthew J Voegtle
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Jahan M Dawlaty
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
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6
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Capistran BA, Yuwono SH, Moemeni M, Maity S, Vahdani A, Borhan B, Jackson JE, Piecuch P, Dantus M, Blanchard GJ. Intramolecular Relaxation Dynamics Mediated by Solvent-Solute Interactions of Substituted Fluorene Derivatives. Solute Structural Dependence. J Phys Chem B 2021; 125:12486-12499. [PMID: 34752096 DOI: 10.1021/acs.jpcb.1c06475] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Several fluorene derivatives exhibit excited-state reactivity and relaxation dynamics that remain to be understood fully. We report here the spectral relaxation dynamics of two fluorene derivatives to evaluate the role of structural modification in the intramolecular relaxation dynamics and intermolecular interactions that characterize this family of chromophores. We have examined the time-resolved spectral relaxation dynamics of two compounds, NCy-FR0 and MK-FR0, in protic and aprotic solvents using steady-state and time-resolved emission spectroscopy and quantum chemical computations. Both compounds exhibit spectral relaxation characteristics similar to those seen in FR0, indicating that hydrogen bonding interactions between the chromophore and solvent protons play a significant role in determining the relaxation pathways available to three excited electronic states.
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Affiliation(s)
- Briana A Capistran
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Stephen H Yuwono
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Mehdi Moemeni
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Soham Maity
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Aria Vahdani
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Babak Borhan
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - James E Jackson
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Piotr Piecuch
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States.,Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States
| | - Marcos Dantus
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States.,Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States
| | - G J Blanchard
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
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7
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Capistran BA, Yuwono SH, Moemeni M, Maity S, Vahdani A, Borhan B, Jackson JE, Piecuch P, Dantus M, Blanchard GJ. Excited-State Dynamics of a Substituted Fluorene Derivative. The Central Role of Hydrogen Bonding Interactions with the Solvent. J Phys Chem B 2021; 125:12242-12253. [PMID: 34726920 PMCID: PMC9254887 DOI: 10.1021/acs.jpcb.1c06474] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Substituted fluorene structures have demonstrated unusual photochemical properties. Previous reports on the substituted fluorene Schiff base FR0-SB demonstrated super photobase behavior with a ΔpKb of ∼14 upon photoexcitation. In an effort to understand the basis for this unusual behavior, we have examined the electronic structure and relaxation dynamics of the structural precursor of FR0-SB, the aldehyde FR0, in protic and aprotic solvents using time-resolved fluorescence spectroscopy and quantum chemical calculations. The calculations show three excited singlet states in relatively close energetic proximity. The spectroscopic data are consistent with relaxation dynamics from these electronic states that depend on the presence and concentration of solvent hydroxyl functionality. These results underscore the central role of solvent hydrogen bonding to the FR0 aldehyde oxygen in mediating the relaxation dynamics within this molecule.
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Affiliation(s)
- Briana A Capistran
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Stephen H Yuwono
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Mehdi Moemeni
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Soham Maity
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Aria Vahdani
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Babak Borhan
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - James E Jackson
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Piotr Piecuch
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States
| | - Marcos Dantus
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States
| | - G J Blanchard
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
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8
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Alamudun SF, Tanovitz K, Espinosa L, Fajardo A, Galvan J, Petit AS. Structure-Photochemical Function Relationships in the Photobasicity of Aromatic Heterocycles Containing Multiple Ring Nitrogen Atoms. J Phys Chem A 2021; 125:13-24. [PMID: 33373234 DOI: 10.1021/acs.jpca.0c07013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Photobases are compounds that become more basic when promoted to an excited electronic state. Previous experimental and computational studies have demonstrated that several quinoline and quinoline-derived compounds are strong photobases (pKa* > 14). Moreover, the strength of photobasicity was shown to depend strongly on the identity and position of the substituent group(s), with the strongest photobases having multiple electron-donating substituents on a fused benzene ring as opposed to the ring containing the photobasic nitrogen atom. These electron-donating substituents build up electron density on one side of the molecule that shifts onto the nitrogen-containing ring in the electronic transition. This shift in electron density produces an increase in negative charge on the ring nitrogen atom responsible for the photobasicity. In this paper, we expand on our previous investigation to study the effect of an additional ring nitrogen atom on photobasicity in aromatic heterocycles. In particular, we consider how the thermodynamic driving force for excited-state protonation can be tuned by changing the relative placement of the ring nitrogen atoms and varying the position and number of electron-donating substituents. In the set of 112 molecules screened, we identified 42 strong photobases with generally comparable pKa* but lower vertical excitation energies than the quinoline derivatives with only a single ring nitrogen atom. We additionally explored photobasicity in substituted azaindole and carboline derivatives, identifying 76 strongly photobasic compounds with pKa* as large as 22.6 out of the 155 compounds that we considered. Overall, this work provides new insights into the design principles necessary to develop next-generation photocatalysts that employ photobasicity.
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Affiliation(s)
- Sophya F Alamudun
- Department of Chemistry and Biochemistry, California State University-Fullerton, Fullerton, California 92834-6866, United States
| | - Kyle Tanovitz
- Department of Chemistry and Biochemistry, California State University-Fullerton, Fullerton, California 92834-6866, United States
| | - Lanette Espinosa
- Department of Chemistry and Biochemistry, California State University-Fullerton, Fullerton, California 92834-6866, United States
| | - April Fajardo
- Department of Chemistry and Biochemistry, California State University-Fullerton, Fullerton, California 92834-6866, United States
| | - John Galvan
- Department of Chemistry and Biochemistry, California State University-Fullerton, Fullerton, California 92834-6866, United States
| | - Andrew S Petit
- Department of Chemistry and Biochemistry, California State University-Fullerton, Fullerton, California 92834-6866, United States
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9
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Sittig M, Tom JC, Elter JK, Schacher FH, Dietzek B. Quinoline Photobasicity: Investigation within Water-Soluble Light-Responsive Copolymers. Chemistry 2021; 27:1072-1079. [PMID: 32986286 PMCID: PMC7839697 DOI: 10.1002/chem.202003815] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 09/14/2020] [Indexed: 01/13/2023]
Abstract
Quinoline photobases exhibit a distinctly higher pKa in their electronically excited state than in the ground state, thereby enabling light-controlled proton transfer reactions, for example, in molecular catalysis. The absorption of UV light translates to a pKa jump of approximately 10 units, as established for small-molecule photobases. This contribution presents the first synthesis of quinoline-based polymeric photobases prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization. The integration of quinolines as photobase chromophores within copolymers offers new possibilities for light-triggered proton transfer in nanostructured materials, that is, in nanoparticles, at surfaces, membranes and interfaces. To exploit the light-triggered reactivity of photobases within such materials, we first investigated how the ground- and excited-state properties of the quinoline unit changes upon polymer integration. To address this matter, we combined absorption and emission spectroscopy with time-resolved transient-absorption studies to reveal photoinduced proton-transfer dynamics in various solvents. The results yield important insights into the thermodynamic and kinetic properties of these polymeric quinoline photobases.
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Affiliation(s)
- Maria Sittig
- Department of Functional InterfacesLeibniz Institute of Photonic Technology JenaAlbert-Einstein-Strasse 907745JenaGermany
- Institute of Physical Chemistry and Abbe Center of PhotonicsFriedrich-Schiller-University JenaHelmholtzweg 407743JenaGermany
- Jena Center for Soft Matter (JCSM)Friedrich Schiller University JenaPhilosophenweg 707743JenaGermany
| | - Jessica C. Tom
- Institute of Organic Chemistry and Macromolecular Chemistry (IOMC)Friedrich Schiller University JenaHumboldtstrasse 1007743JenaGermany
- Jena Center for Soft Matter (JCSM)Friedrich Schiller University JenaPhilosophenweg 707743JenaGermany
| | - Johanna K. Elter
- Institute of Organic Chemistry and Macromolecular Chemistry (IOMC)Friedrich Schiller University JenaHumboldtstrasse 1007743JenaGermany
- Jena Center for Soft Matter (JCSM)Friedrich Schiller University JenaPhilosophenweg 707743JenaGermany
| | - Felix H. Schacher
- Institute of Organic Chemistry and Macromolecular Chemistry (IOMC)Friedrich Schiller University JenaHumboldtstrasse 1007743JenaGermany
- Jena Center for Soft Matter (JCSM)Friedrich Schiller University JenaPhilosophenweg 707743JenaGermany
| | - Benjamin Dietzek
- Department of Functional InterfacesLeibniz Institute of Photonic Technology JenaAlbert-Einstein-Strasse 907745JenaGermany
- Institute of Physical Chemistry and Abbe Center of PhotonicsFriedrich-Schiller-University JenaHelmholtzweg 407743JenaGermany
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10
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Rabe EJ, Goldwyn HJ, Hwang D, Masiello DJ, Schlenker CW. Intermolecular Hydrogen Bonding Tunes Vibronic Coupling in Heptazine Complexes. J Phys Chem B 2020; 124:11680-11689. [PMID: 33315409 DOI: 10.1021/acs.jpcb.0c07719] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To better understand how hydrogen bonding influences the excited-state landscapes of aza-aromatic materials, we studied hydrogen-bonded complexes of 2,5,8-tris (4-methoxyphenyl)-1,3,4,6,7,9,9b-heptaazaphenalene (TAHz), a molecular photocatalyst related to graphitic carbon nitride, with a variety of phenol derivatives (R-PhOH). By varying the electron-withdrawing character of the para-substituent on the phenol, we can modulate the strength of the hydrogen bond. Using time-resolved photoluminescence, we extract a spectral component associated with the R-PhOH-TAHz hydrogen-bonded complex. Surprisingly, we noticed a striking change in the relative amplitude of vibronic peaks in the TAHz-centered emission as a function of R-group on phenol. To gain a physical understanding of these spectral changes, we employed a displaced-oscillator model of molecular emission to fit these spectra. This fit assumes that two vibrational modes are dominantly coupled to the emissive electronic transition and extracts their frequencies and relative nuclear displacements (related to the Huang-Rhys factor). With the aid of quantum chemical calculations, we found that heptazine ring-breathing and ring-puckering modes are likely responsible for the observed vibronic progression, and both modes indicate decreasing molecular distortion in the excited state with increasing hydrogen bond strength. This finding offers new insights into intermolecular excited-state hydrogen bonding, which is a crucial step toward controlling excited-state proton-coupled electron transfer and proton transfer reactions.
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Affiliation(s)
- Emily J Rabe
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Harrison J Goldwyn
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Doyk Hwang
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - David J Masiello
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Cody W Schlenker
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.,Molecular Engineering and Sciences Institute, University of Washington, Seattle, Washington 98195-1652, United States.,Clean Energy Institute, University of Washington, Seattle, Washington 98195-1653, United States
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11
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Lahiri J, Moemeni M, Magoulas I, Yuwono SH, Kline J, Borhan B, Piecuch P, Jackson JE, Blanchard GJ, Dantus M. Steric effects in light-induced solvent proton abstraction. Phys Chem Chem Phys 2020; 22:19613-19622. [PMID: 32936138 DOI: 10.1039/d0cp03037f] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The significance of solvent structural factors in the excited-state proton transfer (ESPT) reactions of Schiff bases with alcohols is reported here. We use the super photobase FR0-SB and a series of primary, secondary, and tertiary alcohol solvents to illustrate the steric issues associated with solvent to photobase proton transfer. Steady-state and time-resolved fluorescence data show that ESPT occurs readily for primary alcohols, with a probability proportional to the relative -OH concentration. For secondary alcohols, ESPT is greatly diminished, consistent with the barrier heights obtained using quantum chemistry calculations. ESPT is not observed in the tertiary alcohol. We explain ESPT using a model involving an intermediate hydrogen-bonded complex where the proton is "shared" by the Schiff base and the alcohol. The formation of this complex depends on the ability of the alcohol solvent to achieve spatial proximity to and alignment with the FR0-SB* imine lone pair stabilized by the solvent environment.
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Affiliation(s)
- Jurick Lahiri
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
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12
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Alamudun SF, Tanovitz K, Fajardo A, Johnson K, Pham A, Jamshidi Araghi T, Petit AS. Structure-Photochemical Function Relationships in Nitrogen-Containing Heterocyclic Aromatic Photobases Derived from Quinoline. J Phys Chem A 2020; 124:2537-2546. [PMID: 32196344 DOI: 10.1021/acs.jpca.9b11375] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Photobases are compounds that become strong bases after electronic excitation. Recent experimental studies have highlighted the photobasicity of the 5-R quinoline compounds, demonstrating a strong substituent dependence to the pKa*. In this paper, we describe our systematic study of how the thermodynamic driving force for photobasicity is tuned through substituents in four families of nitrogen-containing heterocyclic aromatics. We show that substituent position and identity both significantly impact the pKa*. We demonstrate that the substituent effects are additive and identify many disubstituted compounds with substantially greater photobasicity than the most photobasic 5-R quinoline compound identified previously. We show that the addition of a second fused benzene ring to quinoline, along with two electron-donating substituents, lowers the S0 → SPBS vertical excitation energy into the visible region while still maintaining a pKa* > 14. Overall, the structure-function relationships developed in this study provide new insights to guide the development of new photocatalysts that employ photobasicity.
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Affiliation(s)
- Sophya F Alamudun
- Department of Chemistry and Biochemistry, California State University, Fullerton, Fullerton, California 92834-6866, United States
| | - Kyle Tanovitz
- Department of Chemistry and Biochemistry, California State University, Fullerton, Fullerton, California 92834-6866, United States
| | - April Fajardo
- Department of Chemistry and Biochemistry, California State University, Fullerton, Fullerton, California 92834-6866, United States
| | - Kaitlind Johnson
- Department of Chemistry and Biochemistry, California State University, Fullerton, Fullerton, California 92834-6866, United States
| | - Andy Pham
- Department of Chemistry and Biochemistry, California State University, Fullerton, Fullerton, California 92834-6866, United States
| | - Tina Jamshidi Araghi
- Department of Chemistry and Biochemistry, California State University, Fullerton, Fullerton, California 92834-6866, United States
| | - Andrew S Petit
- Department of Chemistry and Biochemistry, California State University, Fullerton, Fullerton, California 92834-6866, United States
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