Photoisomerization dynamics of spiropyran: A surface-hopping investigation

In the present work, we performed a computational investigation of the photoisomerization of spiro[1,3-dihydroindole-2,2′-chromene] [spiropyran (SP)] to merocyanine. The electronic energies and wavefunctions were obtained from configuration interaction calculations, using the floating occupation molecular orbital method, in a semiempirical framework. The parameters of the semiempirical Hamiltonian were re-optimized to reproduce ab initio literature data for SP. In our dynamics simulations, we considered, besides S0, the excited states S1, S2, and S3, which are very close in energy in the Franck–Condon region. We obtained a singlet lifetime of 0.67 ps, in line with the experimental results. We found the photoisomerization quantum yield to depend on the electronic state initially populated.