Mechanism of ultrafast non-reactive deactivation of the retinal chromophore in non-polar solvents,Physical Chemistry Chemical Physics

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Mechanism of ultrafast non-reactive deactivation of the retinal chromophore in non-polar solvents
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2017-09-14 00:00:00 , DOI: 10.1039/c7cp03293e
M. Mališ _{1,

2,

3,

4,

5} , J. Novak _{1,

2,

3,

4} , G. Zgrablić _{6,

7,

8,

9,

10} , F. Parmigiani _{6,

7,

8,

9,

11} , N. Došlić _{1,

2,

3,

4}

Affiliation

The photoisomerization of the all-trans protonated Schiff base of retinal (SBR⁺) in solution is highly inefficient. The present theoretical and experimental investigation aims at disclosing the mechanisms of ultrafast, non-reactive relaxation of SBR⁺ that lead to the drastic decrease in the isomerization yield in non-polar solvents. Our pump–probe measurements demonstrate the sensitivity of the all-trans SBR⁺ excited-state dynamics on the electrostatic interaction with the surrounding counterions and the crucial importance of the chromophore microenvironment. Our computational study focuses for the first time on the retinal chromophore–counterion pairs that are formed in non-polar solvents. By employing TDDFT-based nonadiabatic dynamics simulations and ADC(2) reaction paths calculations we found that internal conversion from the initially excited state to an inter-molecular charge transfer state with excitation localized on the counterion, leads to dissociation of the chromophore–counterion pair and to the abortion of isomerization. Barriers to conical intersection with the inter-molecular charge transfer state were found in the range 0.42–0.67 eV at the ADC(2) level. The existence of a barrier along the non-reactive relaxation pathways explains the observation that in solution the excitation on the blue edge of the SBR⁺ absorption leads to decrease in the isomerization yield with respect to the excitation at the red edge.

中文翻译：

非极性溶剂中视网膜发色团超快非反应性失活的机理

溶液中视网膜全反式质子化席夫碱（SBR ⁺）的光异构化效率很低。当前的理论和实验研究旨在揭示超快，非反应性的SBR ⁺弛豫机理，该机理导致非极性溶剂中异构化收率的急剧下降。我们的泵浦探针测量结果证明了全反式SBR ⁺与周围抗衡离子的静电相互作用的激发态动力学，以及生色团微环境的至关重要性。我们的计算研究首次关注在非极性溶剂中形成的视网膜发色团-抗衡离子对。通过使用基于TDDFT的非绝热动力学模拟和ADC（2）反应路径计算，我们发现内部的从初始激发态到分子间电荷转移态的内部转换，激发态位于反荷离子上，导致发色团-反荷尔蒙对解离并导致异构化的失败在ADC（2）的水平上，与分子间电荷转移状态的圆锥形相交的壁垒在0.42-0.67 eV的范围内。⁺吸收导致相对于红色边缘处的激发，异构化产率降低。

更新日期：2017-09-25

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