The Structure of the Nonadiabatic Photochemical Trans → Cis Isomerization Channel in All-Trans Octatetraene

Garavelli, Marco; Celani, Paolo; Yamamoto, Naoko; Bernardi, Fernando; Robb, Michael A.; Olivucci, Massimo

doi:10.1021/ja961707h

Cited by 56 publications

(67 citation statements)

References 8 publications

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“…25 A low-temperature study of 1,3,5,7-octatetraene in n-hexane indicated that the photoisomerization in the S 1 state occurs adiabatically with a ∼950 cm -1 barrier before decaying to the ground state. 26 In contrast, our work 24 and theoretical calculations by Robb and co-workers 19 suggested that transcis isomerization induces the opening of an efficient nonadiabatic radiationless deactivation channel from the S 1 to S 0 state.…”

Section: Introductionmentioning

confidence: 64%

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Excited-State Dynamics of all-trans-1,3,5,7-Octatetraene in Solution. Direct Observation of Internal Conversion from the S₂ to S₁ State and Relaxation Processes in the S₁ State

et al. 2001

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Femtosecond transient absorption spectroscopy was used to study the excited-state dynamics of the S 2 (1 1 B u ) state all-trans-1,3,5,7-octatetraene in solution. The sample was excited at 267 nm and probed at eleven different wavelengths from 340 to 540 nm. Combined with the picosecond fluorescence spectroscopy, this study allows direct observation of the initial excited-state dynamics of all-trans-1,3,5,7-octatetraene and the subsequent relaxation process to the ground state. Transient absorption signals decaying on time scales of about 0.4 ps were seen at wavelengths longer than 480 nm. These absorptions are assigned to an S n -S 2 transition, indicating that internal conversion from the S 2 to S 1 state takes place on a 400-fs time scale. The transient absorption signals observed at shorter wavelengths, which correspond to the S n -S 1 transition, decay on a picosecond to subnanosecond time scale. A weak fluorescence at about 300-350 nm, originating from the S 2 state, and a strong fluorescence at about 350-500 nm, from the S 1 state, were observed. The time profile of the S 2 fluorescence signal is almost equal to the instrument response function, and the lifetime is estimated to be faster than 5 ps. This observation is consistent with the results of transient absorption signals. The S 1 fluorescence signal consists of two decay components. The average lifetimes are 0.88 ns in acetonitrile and 2.0 ns in n-hexane. Nonexponential decay of the fluorescence may result from an equilibrium mixture of the fluorescent state and the conformationally relaxed state. The fluorescence intensity ratio of S 2 to S 1 in solution is much different from that observed in the gas phase. This means that the efficiency of internal conversion increases significantly in solution because of the solute-solvent interactions that are absent in the gas phase. We discuss differences in the excited-state dynamics between 1,3,5-hexatriene and 1,3,5,7-octatetraene.

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Section: Introductionmentioning

confidence: 64%

“…Robb and co-workers calculated the S 1 and S 0 potential energy surfaces of trans-1,3,5-hexatriene and all-trans-1,3,5,7-octatetraene. 18,19 They found that the barrier height of trans-cis isomerization is less than about 4 and 25 kJ/mol in the S 1 state, respectively.…”

Section: Introductionmentioning

confidence: 99%

Excited-State Dynamics of all-trans-1,3,5,7-Octatetraene in Solution. Direct Observation of Internal Conversion from the S₂ to S₁ State and Relaxation Processes in the S₁ State

et al. 2001

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“…(In short-chain polyenes, the former double bonds practically become single bonds in S 1 [see Qualitative PES].) Indeed, calculation for hexatriene (32) and octatetraene (34) revealed such an adiabatic process and predicted an activation energy that is not much higher than that for ground-state rotamerization. It is expected to have a chance to occur in addition to relaxation through the CI only if the latter also requires some activation energy; this is the case for octatetraene and derivatives whose excited state has very long lifetimes (see Comparison with Experiments, in Particular with Observed Cases of HT).…”

Section: Nonpolar Conjugated Olefinsmentioning

confidence: 99%

Structure of the Conical Intersections Driving the cis—trans Photoisomerization of Conjugated Molecules

et al. 2003

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“…Also, the results of Fuss and coworkers (24) showed that the two-bond-flip product was formed in the absence of any one-bond-twist product, a feature more consistent with the concerted HT-n mechanism than the stepwise mechanism. And the recent calculations on minimum energy pathways for deactivation of excited dienes and polyenes (29,30) showed that, even in isolation, two-bond twist is not a prohibitively high-energy pathway. In short, we believe HT-n is a concerted diabatic process, higher in energy than OBF, yet becoming observable when the latter is suppressed in confined media.…”

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confidence: 99%

The case of medium-dependent dual mechanisms for photoisomerization: One-bond-flip and Hula-Twist

Liu

Hammond²

2000

Proc. Natl. Acad. Sci. U.S.A.

170

130

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This paper critically reviews examples in the literature of photochemical cis-trans isomerization paying particular attention to the medium effect and accompanied conformational changes. A case is made that the Hula-Twist mechanism, postulated in 1985 as a photochemical reaction pathway for a polyene chromophore imbedded in a protein binding cavity such as those of rhodopsin and bacteriorhodopsin, is also a dominant reaction pathway for a diene, or a longer polyene confined in a rigid (relative to isomerization rate) medium. The conventional one-bond-flip process is the preferred reaction pathway in a fluid medium. While defining experiments are proposed, this dual mechanistic approach successfully accounts for all examples in the literature on photoisomerization reactions whether involving conformational changes or not.

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The Structure of the Nonadiabatic Photochemical Trans → Cis Isomerization Channel in All-Trans Octatetraene

Cited by 56 publications

References 8 publications

Excited-State Dynamics of all-trans-1,3,5,7-Octatetraene in Solution. Direct Observation of Internal Conversion from the S₂ to S₁ State and Relaxation Processes in the S₁ State

Excited-State Dynamics of all-trans-1,3,5,7-Octatetraene in Solution. Direct Observation of Internal Conversion from the S₂ to S₁ State and Relaxation Processes in the S₁ State

Structure of the Conical Intersections Driving the cis—trans Photoisomerization of Conjugated Molecules

The case of medium-dependent dual mechanisms for photoisomerization: One-bond-flip and Hula-Twist

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The Structure of the Nonadiabatic Photochemical Trans → Cis Isomerization Channel in All-Trans Octatetraene

Cited by 56 publications

References 8 publications

Excited-State Dynamics of all-trans-1,3,5,7-Octatetraene in Solution. Direct Observation of Internal Conversion from the S2 to S1 State and Relaxation Processes in the S1 State

Excited-State Dynamics of all-trans-1,3,5,7-Octatetraene in Solution. Direct Observation of Internal Conversion from the S2 to S1 State and Relaxation Processes in the S1 State

Structure of the Conical Intersections Driving the cis—trans Photoisomerization of Conjugated Molecules

The case of medium-dependent dual mechanisms for photoisomerization: One-bond-flip and Hula-Twist

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Excited-State Dynamics of all-trans-1,3,5,7-Octatetraene in Solution. Direct Observation of Internal Conversion from the S₂ to S₁ State and Relaxation Processes in the S₁ State

Excited-State Dynamics of all-trans-1,3,5,7-Octatetraene in Solution. Direct Observation of Internal Conversion from the S₂ to S₁ State and Relaxation Processes in the S₁ State