Ultrafast spectroscopic study on non-adiabatic UV protection mechanism of hemicyanines

Abstract

In this work, we firstly elucidated the ultra-violet light protection dynamics mechanism of the typical hemicyanines, i.e. Hemicy and DHemicy, by combining the theoretical calculation method and the transient absorption spectra. It is theoretically and experimentally demonstrated that both Hemicy and DHemicy have strong absorption in UVC (200−280 nm), UVB (280−300 nm), and UVA (320−400 nm) regions. More-over, after absorbing energy, Hemicy and DHemicy can jump into the excited states. Subsequently, Hemicy and DHemicy relax to S0 states from S1 states rapidly by the non-adiabatic transition at the conical intersection point between the potential energy curves of S1 and S0 states, and are accompanied by the trans-cis photoisomerism. The transient absorption spectra show that trans-cis photoisomerization occur within a few picoseconds. Thus, the ultraviolet energy absorbed by Hemicy and DHemicy could be relaxed ultrafastly by the non-adiabatic trans-cis photoisomerization processes.