Tulyabaev Arthur R, Khuzin Artur A, Lukmanov Timur I, Sabirov Denis Sh
Institute of Petrochemistry and Catalysis, Ufa Federal Research Centre, Russian Academy of Sciences, 141 Prospekt Oktyabrya, Ufa, Russia.
Phys Chem Chem Phys. 2024 Mar 27;26(13):10336-10342. doi: 10.1039/d3cp06322d.
The stability of merocyanine forms formed under UV irradiation of a solution of a spiropyran salt, in which an organic part acts as a cation and a compact bromide ion as an anion, their photophysical properties, and the formation mechanism are studied in this work using time-dependent density functional theory. Theoretical calculations show that TTC and CTT are the most stable open forms (the difference in stability energies is 10.5 and 12.0 kcal mol relative to the formation energy of spiropyran, respectively). The simulated absorption bands in the UV spectrum of the merocyanine forms are observed both in the UV region at 308-366 nm and in the visible region at 544-757 nm due to n → π* and π → π* type transitions. We found that the isomerisation mechanism of spiropyran into merocyanine forms includes two key stages: the ring opening to form cisoid merocyanine forms (except unstable TCC) through conical intersection and their subsequent isomerisation to form stable transoid isomers. The length of the C-O bond is 1.97 Å and the C1'-C2'-C3'-C4' angle is 70° in the structure close to conical intersection. The stage that determines the rate of this process is the isomerisation between transoid forms, as in the case of transformation of open merocyanine forms into spiropyran.
本文利用含时密度泛函理论研究了在螺吡喃盐溶液的紫外光照射下形成的部花青形式的稳定性、它们的光物理性质以及形成机理。该螺吡喃盐中有机部分作为阳离子，紧密的溴离子作为阴离子。理论计算表明，TTC和CTT是最稳定的开环形式（相对于螺吡喃的生成能，其稳定能差分别为10.5和12.0 kcal/mol）。由于n→π和π→π型跃迁，在部花青形式的紫外光谱中模拟的吸收带出现在308 - 366 nm的紫外区域以及544 - 757 nm的可见光区域。我们发现螺吡喃异构化为部花青形式的机理包括两个关键阶段：通过锥形交叉开环形成顺式部花青形式（不稳定的TCC除外），以及随后异构化为稳定的反式异构体。在接近锥形交叉的结构中，C - O键长为1.97 Å，C1'-C2'-C3'-C4'角为70°。决定该过程速率的阶段是反式形式之间的异构化，就像开环部花青形式转化为螺吡喃的情况一样。
