ABSTRACT
The ring-opening reactions of perimidinespirocyclohexadienones in the ground and first excited singlet and triplet states were studied at the DFT B3LYP/6-31G**, UB3LYP/6-31G** and CIS/3-21G** levels of theory . It has been found that the thermal isomerization is governed by the non-adiabatic mechanism involving excitation in the triplet state. The irreversible character of the ring-opening photoreaction can be explained by the absence of a local minimum corresponding to the opened form at the S1 potential energy surface. According to the TD DFT calculations the low intense long-wavelength absorption band at 436 nm inherent in perimidinespirocyclohexadienones belongs to a charge-transfer electronic transition involving the frontier orbitals located at different spiroconjugated moieties.
Acknowledgments
This work was supported by the International Scientific Technological Center (project 2117), the program Basic Research and Higher Education (REC-004) and Ministry of Industry and Science of Russian Federation (grant 945. 2003.03).