Isomerization Dynamics of Electronically Coupled but Thermodynamically Decoupled Bisazobenzenes

Abstract

AbstractPhotoresponsive structures composed of multiple photoswitchable units offer the possibility of more diverse and complex control applications. For example, o‐bisazobenzenes (o‐bisABs) show unusual electronic coupling affecting the properties of the individual AB units. In the present work derivatives with amino and acetamido groups were investigated to gain further insight into the photoisomerization pathways of o‐bisABs. Time‐resolved spectroscopic experiments supported by quantum chemical calculations revealed that electronic coupling removes the bias introduced by selective excitation of one AB moiety. In effect, the isomerization ratio between the two photochromic units in o‐bisABs is intrinsically determined by the interplay of electronic coupling and their relative energy. Furthermore, the Z→E thermally activated relaxation of the AB moieties in o‐bisABs is decoupled and proceeds independently for each unit on different timescales.