Photochromic properties of some azomaleimide derivatives and DFT quantum chemical study of thermal cis-trans isomerization pathways

Abstract A systematic study on the dynamics of trans-cis, thermal cis-trans backward and light induced cis-trans isomerization of some azobismaleimide derivatives was performed. Systems under study were N-[4-(carbonylaminoazobenzene)-phenyl]-maleimide (AAzM) and a styrene-maleimide copolymer containing azo units in the side chain (AAzMC). The isomerization reactions were followed by electronic absorption spectra. The kinetics of trans-cis photoisomerization was investigated in six solvents with different polarities. Results revealed that the content of the photostationary state depended on the solvent nature. In turn, the chemical environment had a minor influence on the photoisomerization rate constants. The kinetic and thermodynamic activation parameters were evaluated according to Arrhenius and Eyring equations. The theoretical calculations based on density functional theory (DFT) were employed to identify the mechanism of the thermal isomerization in AAzM. In our results, the thermal cis-trans isomerization of azobismaleimide AAzM followed an inversion assisted by rotation pathway in the S0 state.