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.