Relaxation of the Electronic Excitation of the Molecule in the Path Spiropyran ↔ Merocyanine

Authors P.O. Kondratenko1 , Yu.M. Lopatkin2 , T.M. Sakun1

1Aerospace Institute, National Aviation University, 1, Lyubomyr Guzar Ave., 03058 Kyiv, Ukraine

2Sumy State University, 2, Rimsky-Korsakov st., 40007 Sumy, Ukraine

Issue Volume 14, Year 2022, Number 6
Dates Received 03 October 2022; revised manuscript received 21 December 2022; published online 27 December 2022
Citation P.O. Kondratenko, Yu.M. Lopatkin, et al., J. Nano- Electron. Phys. 14 No 6, 06020 (2022)
PACS Number(s) 31.50.Df, 82.20.Wt
Keywords Spiropyran, Merocyanine, Relaxation of electronic excitation, Phase transition (6) , Mechanisms of photoconversion of spiropyran to merocyanine and vice versa.

Quantum chemical studies of the geometric and energy structure of spiropyran and merocyanine molecules, as well as intermediate states corresponding to the optimized geometry of molecules at different distances between the spiroatom and the oxygen atom are carried out. It is established that when the RCspiro-O distance increases to 2.375 Å, a phase transition occurs in the molecule structure. It is shown that the geometric structure of the spiropyran molecule is unique. As the RCspiro-O distance increases, the energy of the electronic system of the molecule increases. At the same time, hybridization of AO of the spiroatom gradually changes. Excitation of the spiropyran molecule to the S1 state, which is dissociative, causes the conversion of spiropyran to merocyanine. The energy structure of the merocyanine molecule is studied and it is shown that in this case, the relaxation of the electronic excitation includes TTT-TTS isomerization, as well as interconversion to the T1 and T2 states. In addition, it becomes possible to reduce the distance RCspiro-O to the phase transition. The perturbation caused by the phase transition causes the conversion of the excited molecule to the ground state, resulting in the photoconversion of spiropyran to merocyanine and vice versa. The described mechanism requires that the quantum yield of the photoconversion of spiropyran to merocyanine exceeds the quantum yield of the reverse transition.

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