Non-adiabatic dynamics simulation exploration of the wavelength-dependent photoinduced relaxation mechanism of trans-N-1-methyl-2-(tolylazo) imidazole in the gas phase

Abstract

A comprehensive picture of the photoinduced non-adiabatic relaxation dynamics of trans-N-1-methyl-2-(tolylazo) imidazole (trans-MTAI) in different electronic excited states has been revealed using on-the-fly surface hopping method at the ab initio CASSCF level. The decay process is mainly driven by the twisting motion around the NN double bond upon photoexcitation to the S₁ state. However, after photoexcitation to the S₂ state, an ultrafast S₂ → S₁ non-adiabatic transition occurs in less than 150 fs accompanied by a stretching of the NN bond. Afterwards, an additional NNC bending reaction pathway is activated, competing with the photoisomerization channel. The activation of multiple reaction pathways following excitation to the S₂ state is expected to provide a reasonable explanation for the wavelength-dependent isomerization property of trans-MTAI.