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Brady RP, Zhang C, DeFrancisco JR, Barrett BJ, Cheng L, Bragg AE. Multiphoton Control of 6π Photocyclization via State-Dependent Reactant-Product Correlations. J Phys Chem Lett 2021; 12:9493-9500. [PMID: 34559534 DOI: 10.1021/acs.jpclett.1c02353] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Multiphoton excitation promises opportunities for opening new photochemical reaction pathways and controlling photoproduct distributions. We demonstrate photonic control of the 6π photocyclization of ortho-terphenyl to make 4a,4b-dihydrotriphenylene (DHT). Using pump-repump-probe spectroscopy we show that 1 + 1' excitation to a high-lying reactant electronic state generates a metastable species characterized by a red absorption feature that accompanies a repump-induced depletion in the one-photon trans-dihydro product (trans-DHT); signatures of the new photoproduct are clearer for a structural analogue of the reactant that is sterically inhibited against one-photon cyclization. Quantum-chemical computations support assignment of this species to cis-DHT, which is accessible photochemically along a disrotatory coordinate from high-lying electronic states reached by 1 + 1' excitation. We use time-resolved spectroscopy to track photochemical dynamics producing cis-DHT. In total, we demonstrate that selective multiphoton excitation opens a new photoreaction channel in these photocyclizing reactants by taking advantage of state-dependent correlations between reactant and product electronic states.
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Affiliation(s)
- Ryan P Brady
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Chaoqun Zhang
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Justin R DeFrancisco
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Brandon J Barrett
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Lan Cheng
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Arthur E Bragg
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
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Snyder JA, Bragg AE. Ultrafast Pump-Repump-Probe Photochemical Hole Burning as a Probe of Excited-State Reaction Pathway Branching. J Phys Chem Lett 2018; 9:5847-5854. [PMID: 30226782 DOI: 10.1021/acs.jpclett.8b02489] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We demonstrate pump-repump-probe (PRP) transient hole burning as a spectroscopic tool for differentiating reactive from nonreactive deactivation of excited photochemical reactants observed by transient absorption spectroscopy (TAS). This method utilizes a time-delayed, wavelength-tunable ultrafast pulse to alter the excited reactant population, with the impact of "repumping" quantified through depletions in photoproduct absorption. We apply this approach to characterize dynamics affecting the nonadiabatic photocyclization efficiency to form S0 dihydrotriphenylene (DHT) following 266 nm excitation of ortho-terphenyl (OTP). TAS studies revealed bimodal deactivation of OTP*, but neither relaxation time scale (700 fs and 3.0 ps) could be assigned unambiguously to DHT formation due to overlap of excited-state and product spectra. PRP studies reveal that S1 OTP only cyclizes on the slower of these time scales, with the faster process attributable to nonreactive deactivation. We demonstrate that this method offers greater photochemical insights without assuming models to globally fit spectral transients collected by TAS.
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Affiliation(s)
- Joshua A Snyder
- Department of Chemistry , Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
| | - Arthur E Bragg
- Department of Chemistry , Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
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Snyder JA, Grüninger P, Bettinger HF, Bragg AE. BN Doping and the Photochemistry of Polyaromatic Hydrocarbons: Photocyclization of Hexaphenyl Benzene and Hexaphenyl Borazine. J Phys Chem A 2017; 121:8359-8367. [PMID: 28949535 DOI: 10.1021/acs.jpca.7b08190] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Boron-nitrogen doping of polyaromatic hydrocarbon (PAH) materials can be used to tune their electronic properties while preserving the structural characteristics of pure hydrocarbons. Many multicycle PAHs can be synthesized photochemically; in contrast, very little is known about the photochemistry of their BN-doped counterparts. We present results of fs, ns, and μs time-resolved spectroscopic studies on the photoinduced dynamics of hexaphenyl benzene and hexaphenyl borazine in order to examine how BN doping alters photochemical C-C bond formation via 6π electrocyclization as well as the stability of resulting cyclized structures. Ultrafast measurements reveal photoinduced behaviors reflecting differences in excited-state decay pathways for the two molecules, with hexaphenyl borazine relaxing from its excited state with a rate that is 2 orders of magnitude faster than that of hexaphenyl benzene (3.0 vs 428 ps). Tetraphenyl dihydrotriphenylene generated from hexaphenyl benzene is observed to reopen with a ∼2 μs lifetime controlled by entropic stabilization of the cyclized structure; in contrast, photoinduced dynamics appear to be complete within 100 ps after excitation of hexaphenyl borazine. This significant difference in photochemical dynamics is reflected in the cyclodehydrogentation yields obtained for the two reactants (25 vs 0% for hexaphenyl benzene and borazine, respectively). Quantum-chemical computations predict that BN doping gives rise to energetic destabilization and increased singlet diradical character in cyclized structures. These findings indicate that the polarized BN bonds of the borazine core adversely impact photochemical bond formation relative to analogous hydrocarbons.
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Affiliation(s)
- Joshua A Snyder
- Department of Chemistry, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Peter Grüninger
- Institut für Organische Chemie, Universität Tübingen , Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Holger F Bettinger
- Institut für Organische Chemie, Universität Tübingen , Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Arthur E Bragg
- Department of Chemistry, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
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Snyder JA, Grüninger P, Bettinger HF, Bragg AE. Excited-State Deactivation Pathways and the Photocyclization of BN-Doped Polyaromatics. J Phys Chem A 2017. [PMID: 28625051 DOI: 10.1021/acs.jpca.7b04878] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Boron-nitrogen doping of polyaromatic hydrocarbons (PAH), such as borazine-core hexabenzocoronene, presents possibilities for tuning the properties of organic electronics and nanographene materials while preserving structural characteristics of pure hydrocarbons. Previous photochemical studies have demonstrated extension of a borazine-core PAH network (1,2:3,4:5,6-tris(o,o'-biphenylylene)borazine, 1) by photoinduced cyclodehydrogenation. We present steady-state and femtosecond-to-microsecond resolved spectroscopic studies of the photophysics of 1 and a related borazine-core PAH in order to characterize competing excited-state relaxation pathways that determine the efficacy of bond formation by photocyclization. Transient spectra evolve on time scales consistent with S1 fluorescence lifetimes (1-3 ns) to features that persist onto microsecond time scales. Nanosecond-resolved oxygen-quenching measurements reveal that long-lived metastable states are triplets rather than cyclized products. Determination of fluorescence and triplet quantum yields reveal that photochemical bond formation is a minor channel in the relaxation of 1 (∼5% or less), whereas highly efficient fluorescence and intersystem crossing result in negligible photoinduced bond formation in more extended borazine-core networks. Results of computational investigations at the RICC2 level reveal sizable barriers to cyclization on the S1 potential energy surfaces consistent with quantum yields deduced from experiment. Together these barriers and competing photophysical pathways limit the efficiency of photochemical synthesis of BN-doped polyaromatics.
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Affiliation(s)
- Joshua A Snyder
- Department of Chemistry, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Peter Grüninger
- Institut für Organische Chemie, Universität Tübingen , Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Holger F Bettinger
- Institut für Organische Chemie, Universität Tübingen , Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Arthur E Bragg
- Department of Chemistry, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
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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] [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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Younes EA, Zhao Y. Functionalization of pentacene-5,7,12,14-tetraone with geminal enediyne and 1,3-dithiole groups. Org Chem Front 2017. [DOI: 10.1039/c7qo00041c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Pentacene-5,7,12,14-tetraone was subjected to selective olefination and cross-coupling reactions to yield a new class of pentacene-based π-conjugated systems with intriguing structural, electronic, and redox properties.
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Affiliation(s)
- Eyad A. Younes
- Department of Chemistry
- Memorial University
- St. John's
- Canada A1B 3X7
| | - Yuming Zhao
- Department of Chemistry
- Memorial University
- St. John's
- Canada A1B 3X7
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