Sen Saumik, Deupi Xavier
Condensed Matter Theory Group, Laboratory for Theoretical and Computational Physics, Center for Scientific Computing, Theory, and Data, Paul Scherrer Institute, 5232 Villigen, Switzerland.
Swiss Institute of Bioinformatics (SIB), 1015 Lausanne, Switzerland.
ACS Phys Chem Au. 2024 Oct 2;4(6):736-749. doi: 10.1021/acsphyschemau.4c00065. eCollection 2024 Nov 27.
Photoisomerization, the structural alteration of molecules upon absorption of light, is crucial for the function of biological chromophores such as retinal in opsins, proteins vital for vision and other light-sensitive processes. The intrinsic selectivity of this isomerization process (i.e., which double bond in the chromophore is isomerized) is governed by both the inherent properties of the chromophore and its surrounding environment. In this study, we employ the extended multistate complete active space second-order perturbation theory (XMS-CASPT2) method to investigate photoisomerization selectivity in linear conjugated chromophores, focusing on two simple molecular models resembling retinal. By analyzing electronic energies, intramolecular charge separation, and conical intersection topographies in the gas phase, we show that the photoproduct formed by rotation around the double bond near the Schiff base is energetically favored. The topographic differences at the conical intersections leading to different photoproducts reveal differences in photodynamics. In multiphoton excitation, the primary photoproduct typically reverts to the initial configuration rather than rotating around a different double bond. Our study offers new insights into the photodynamics of photoisomerizing double bonds in π-conjugated chromophores. We anticipate that our findings will provide valuable perspectives for advancing the understanding of biological chromophores and for designing efficient photochemical switches with applications in molecular electronics and phototherapy.
光异构化是指分子在吸收光后发生的结构改变，对于视蛋白中视网膜等生物发色团的功能至关重要，视蛋白是视觉和其他光敏感过程中至关重要的蛋白质。这种异构化过程的内在选择性（即发色团中的哪个双键发生异构化）由发色团的固有性质及其周围环境共同决定。在本研究中，我们采用扩展多态完全活性空间二阶微扰理论（XMS-CASPT2）方法来研究线性共轭发色团中的光异构化选择性，重点关注两个类似于视网膜的简单分子模型。通过分析气相中的电子能量、分子内电荷分离和锥形交叉点拓扑结构，我们表明围绕席夫碱附近的双键旋转形成的光产物在能量上更有利。导致不同光产物的锥形交叉点处的拓扑差异揭示了光动力学的差异。在多光子激发中，初级光产物通常会恢复到初始构型，而不是围绕不同的双键旋转。我们的研究为π共轭发色团中光异构化双键的光动力学提供了新的见解。我们预计，我们的发现将为推进对生物发色团的理解以及设计在分子电子学和光疗中有应用的高效光化学开关提供有价值的观点。
