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Hoche J, Schulz A, Dietrich LM, Humeniuk A, Stolte M, Schmidt D, Brixner T, Würthner F, Mitric R. The origin of the solvent dependence of fluorescence quantum yields in dipolar merocyanine dyes. Chem Sci 2019; 10:11013-11022. [PMID: 32206253 PMCID: PMC7069518 DOI: 10.1039/c9sc05012d] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2019] [Accepted: 11/24/2019] [Indexed: 12/26/2022] Open
Abstract
An increasing activation energy barrier to a conical intersection was identified as the reason for higher fluorescence lifetimes and quantum yields for merocyanines in polar solvents.
Fluorophores with high quantum yields are desired for a variety of applications. Optimization of promising chromophores requires an understanding of the non-radiative decay channels that compete with the emission of photons. We synthesized a new derivative of the famous laser dye 4-dicyanomethylen-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM), i.e., merocyanine 4-(dicyanomethylene)-2-tert-butyl-6-[3-(3-butyl-benzothiazol-2-ylidene)1-propenyl]-4H-pyran (DCBT). We measured fluorescence lifetimes and quantum yields in a variety of solvents and found a trend opposite to the energy gap law. This motivated a theoretical investigation into the possible non-radiative decay channels. We propose that a barrier to a conical intersection exists that is very sensitive to the solvent polarity. The conical intersection is characterized by a twisted geometry which allows a subsequent photoisomerization. Transient absorption measurements confirmed the formation of a photoisomer in unpolar solvents, while the measurements of fluorescence quantum yields at low temperature demonstrated the existence of an activation energy barrier.
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Affiliation(s)
- Joscha Hoche
- Institut für Physikalische und Theoretische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . ;
| | - Alexander Schulz
- Institut für Organische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . .,Center for Nanosystems Chemistry & Bavarian Polymer Institute (BPI) , Universität Würzburg , Theodor-Boveri-Weg , 97074 Würzburg , Germany
| | - Lysanne Monika Dietrich
- Institut für Physikalische und Theoretische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . ;
| | - Alexander Humeniuk
- Institut für Physikalische und Theoretische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . ;
| | - Matthias Stolte
- Institut für Organische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . .,Center for Nanosystems Chemistry & Bavarian Polymer Institute (BPI) , Universität Würzburg , Theodor-Boveri-Weg , 97074 Würzburg , Germany
| | - David Schmidt
- Institut für Organische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . .,Center for Nanosystems Chemistry & Bavarian Polymer Institute (BPI) , Universität Würzburg , Theodor-Boveri-Weg , 97074 Würzburg , Germany
| | - Tobias Brixner
- Institut für Physikalische und Theoretische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . ; .,Center for Nanosystems Chemistry & Bavarian Polymer Institute (BPI) , Universität Würzburg , Theodor-Boveri-Weg , 97074 Würzburg , Germany
| | - Frank Würthner
- Institut für Organische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . .,Center for Nanosystems Chemistry & Bavarian Polymer Institute (BPI) , Universität Würzburg , Theodor-Boveri-Weg , 97074 Würzburg , Germany
| | - Roland Mitric
- Institut für Physikalische und Theoretische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . ; .,Center for Nanosystems Chemistry & Bavarian Polymer Institute (BPI) , Universität Würzburg , Theodor-Boveri-Weg , 97074 Würzburg , Germany
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Ma X, Wenzel M, Schmitt HC, Flock M, Reusch E, Mitrić R, Fischer I, Brixner T. Disentangling the photochemistry of benzocyclobutenedione. Phys Chem Chem Phys 2018; 20:15434-15444. [PMID: 29799041 DOI: 10.1039/c8cp01937a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The ultrafast photophysics and photochemistry of benzocyclobutenedione (BCBD) dissolved in dichloromethane is investigated by transient absorption spectroscopy in both the IR and the UV/Vis regime. The molecule is excited at 300 nm to the S3 (ππ*) state and a time scale from roughly 100 fs to several nanoseconds is covered. The initially excited S3 deactivates quickly to the lower-lying S1 (nπ*) state. Three parallel photochemical reaction pathways starting in the S1 state that compete with deactivation to S0 are identified in the transient IR spectra, two of them consisting of a sequence of steps. DFT/TDDFT calculations of the normal modes of the reactant and various photoproducts support the analysis of the transient spectra. The rapid internal conversion (IC) to the S1 state of BCBD is followed by a sub-picosecond vibrational relaxation (VR) to S1 (ν = 0). In parallel BCBD loses one carbonyl group and forms benzocyclopropenone, which subsequently rearranges to cyclopentadienylidene ketene. Ring opening in the S1 (ν = 0) state produces vibrationally hot bisketene, which cools within 22 ps. This reaction competes with the intramolecular rearrangement to singlet oxacarbene, which subsequently converts into the triplet carbene via intersystem crossing (ISC). The late-time product identified in the transient UV/Vis spectra is probably due to dimerization of the carbene. Molecular dynamics (MD) simulations of the early-time photochemistry of BCBD successfully reproduce the formation of the three main photoproducts.
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Affiliation(s)
- Xiaonan Ma
- Institute for Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, 97074 Würzburg, Germany.
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Koch F, Stolte M, Zitzler-Kunkel A, Bialas D, Steinbacher A, Brixner T, Würthner F. Unraveling the structure and exciton coupling for multichromophoric merocyanine dye molecules. Phys Chem Chem Phys 2018; 19:6368-6378. [PMID: 28197618 DOI: 10.1039/c7cp00115k] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The relative orientation of chromophores is a key factor in determining the relationship between the structure and the functionality in molecular multichromophore ensembles. In the case of structurally flexible molecular systems in solution, the task to clarify the relevant effects of accessible chromophore orientations with spectroscopic observations is very demanding. In this study, we address this issue by investigating a series of differently connected multichromophoric systems composed of highly dipolar merocyanine dyes that are systematically varied in their substitution pattern and the number of chromophores attached to a bridging benzene ring. Combining electro-optical absorption (EOA) and UV/Vis spectroscopy with density functional theory (DFT) as well as exciton theory discloses conformational preferences and rationalizes the optical properties of the interacting chromophores. Our findings suggest for all multichromophoric systems there is a relative orientation of the chromophores which compensates for the individual dipole moments of the merocyanine dyes by pointing preferably in opposing directions. These orientations furthermore rationalize the observed spectral properties by partly excitonically-coupled subunits.
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Affiliation(s)
- Federico Koch
- Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
| | - Matthias Stolte
- Center for Nanosystems Chemistry (CNC), Universität Würzburg, Theodor-Boveri-Weg, 97074 Würzburg, Germany and Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
| | - André Zitzler-Kunkel
- Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
| | - David Bialas
- Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
| | - Andreas Steinbacher
- Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
| | - Tobias Brixner
- Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany. and Center for Nanosystems Chemistry (CNC), Universität Würzburg, Theodor-Boveri-Weg, 97074 Würzburg, Germany
| | - Frank Würthner
- Center for Nanosystems Chemistry (CNC), Universität Würzburg, Theodor-Boveri-Weg, 97074 Würzburg, Germany and Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
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