Polarity-dependent barriers and the photoisomerization dynamics of molecules in solution

Hicks, Janice M.; Vandersall, Mark; Sitzmann, E. V.; Eisenthal, Kenneth B.

doi:10.1016/0009-2614(87)85181-3

Cited by 244 publications

(146 citation statements)

References 51 publications

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“…The latter would lead to a change of the rate by a factor of 1.5 at the lowest temperature, which would clearly have been seen within experimental error here. Previous studies similarly observed a temperature dependence much below that of solvent viscosity [11,33,34].…”

Section: Variable Temperature Results Suggest a Near Barrierless Reacmentioning

confidence: 54%

Entropic effects in excited state CT reactions

Pigliucci

Vauthey

Rettig

2009

Chemical Physics Letters

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a b s t r a c tThe kinetics of the dual fluorescence of several derivatives of dimethylaminobenzonitrile (DMABN) has been compared using fs-fluorescence upconversion experiments. Variation of the size and twist angle of the donor (dialkylamino group) suggest a large amplitude solvent-viscosity controlled diffusional twisting motion towards larger twist angles as the rate limiting step.Large rate differences were observed for an ester group as acceptor. Temperature dependent studies indicate that these differences are not connected with different activation barriers but with changes in the Arrhenius preexponential factor. It is argued that conical intersections along the reaction path can bring about these entropy changes.

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Section: Variable Temperature Results Suggest a Near Barrierless Reacmentioning

confidence: 54%

Entropic effects in excited state CT reactions

Pigliucci

Vauthey

Rettig

2009

Chemical Physics Letters

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“…Such a dependence of the excited-state lifetime on both the solvent viscosity and polarity has already been observed in processes involving large-amplitude motion, with a barrier decreasing with solvent polarity. 52,53 Such a situation can be reasonably envisaged here with both the low-frequency twisting and wagging modes of the nitro group and considering the CT character of the S 1 state. Thus, we propose that in nonprotic and polar solvents, NPe*(S 1 ) decays essentially nonradiatively via a lowfrequency coordinate associated with the nitro group.…”

Section: Discussionmentioning

confidence: 99%

Excited-State Dynamics of Nitroperylene in Solution: Solvent and Excitation Wavelength Dependence

2008

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The photophysics and excited-state dynamics of nitroperylene (NPe) in solvents of various polarities and viscosities, including a room-temperature ionic liquid, have been investigated by femtosecond-resolved transient absorption spectroscopy. The excited-state absorption spectrum was found to depend substantially on solvent polarity. In the most polar solvents, it is very similar to that of the NPe radical cation generated upon bimolecular quenching by an electron acceptor, denoting a substantial charge-transfer character of the S 1 state. Contrary to smaller nitroaromatic compounds, NPe in the S 1 state does not undergo ultrafast intersystem crossing (ISC) but decays mainly by internal conversion (IC). In nonprotic solvents, IC involves low-frequency modes with large amplitude motion associated with the nitro group and depends on both the solvent viscosity and polarity. It takes place on a 100 ps time scale in acetonitrile, while in cyclohexane, it is slow enough for ISC to become competitive. Moreover, both the fluorescence quantum yield and the excited-state dynamics were found to differ, depending on which side of the S 0 -S 1 absorption band excitation was performed. This dependence is explained by the inhomogeneous nature of the absorption spectrum arising from a distribution of twist angles of the nitro group relative to the aromatic plane. On the other hand, such excitation wavelength effects were not observed in protic solvents, where the excited-state lifetime was found to be substantially shorter than that in nonprotic solvents. This behavior is rationalized in terms of a H-bonding interaction, which limits the torsional disorder of NPe and favors ultrafast nonradiative deactivation of the excited state. Transient absorption measurements performed for comparative purpose with nitropyrene in acetonitrile confirm the occurrence of ultrafast ISC in smaller nitroaromatic compounds.

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“…99,100 For example, if the transition state is more polar, the reaction rate increases with solvent polarity. This is probably the case for 1 and 3, for which the fluorescence time constants are clearly larger in nonpolar solvents, independently of their viscosity.…”

Section: Discussionmentioning

confidence: 99%

Tuning the Excited-State Dynamics of GFP-Inspired Imidazolone Derivatives

et al. 2009

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The excited-state dynamics of five derivatives of the GFP-chromophore, which differ by the position and nature of their substituents, has been investigated in solvents of various viscosity and polarity and in rigid media using femtosecond-resolved spectroscopy. In polar solvents of low viscosity, like acetonitrile or methanol, the fluorescence decays of all compounds are multiexponential, with average lifetimes of the order of a few picoseconds, whereas in rigid matrices (polymer films and low temperature glasses), they are single exponential with lifetimes of the order of a few nanoseconds and fluorescence quantum yields close to unity. Global analysis of the fluorescence decays recorded at several wavelengths and of the transient absorption spectra reveals the presence of several excited-state populations with slightly different fluorescence and absorption spectra and with distinct lifetimes. These populations are attributed to the existence of multiple ground-state conformers. From the analysis of the dependence of the excited-state dynamics on the solvent and on the nature of the substituents, it follows that the nonradiative deactivation of all these excited chromophores involves an intramolecular coordinate with large amplitude motion. However, depending on the solvent and substituent, additional channels, namely, inter-and intramolecular hydrogen bond assisted nonradiative deactivation, are operative. This allows tuning of the excited-state lifetime of the chromophore. Finally, an ultrafast photoinduced intramolecular charge transfer is observed in polar solvents with one derivative bearing a dimethylaminophenyl substituent.

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Polarity-dependent barriers and the photoisomerization dynamics of molecules in solution

Cited by 244 publications

References 51 publications

Entropic effects in excited state CT reactions

Entropic effects in excited state CT reactions

Excited-State Dynamics of Nitroperylene in Solution: Solvent and Excitation Wavelength Dependence

Tuning the Excited-State Dynamics of GFP-Inspired Imidazolone Derivatives

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