Theoretical study of the cis–trans isomerization mechanism of a pendant metal-bound azobenzene

Abstract

In this paper, we performed density-functional theory (DFT) at the B3LYP/6-311++G(d,p) & LANL2DZ quantum level to probe the thermal cis → trans isomerization of Re(CO)₃–AB, a diimine ligand with an azo group substituent. We have searched for the transition states (TS) on the S₀ and T₁ potential energy surfaces and detected two inversion transition states TS-inv-1 and TS-inv-2 following a rotation-assisted inversion mechanism. In the T₁ state, only the rotation pathway exists with the energy barrier 1.88 eV. We also investigated the photoisomerization pathway, the potential energy profiles of the vertical excitation for the excited states T₁, S₁, T₂ and S₂ were calculated, and we analyzed two possible isomerization routes through the inversion and rotation pathways. In addition, we probed the properties of the isomerization of the azo portion caused by excitation of the MLCT bands.