Photoisomerization of a Maleonitrile‐Type Salen Schiff Base and Its Application in Fine‐Tuning Infinite Coordination Polymers

Strategically designed salen ligand 2,3‐bis[4‐(di‐p‐tolylamino)‐2‐hydroxybenzylideneamino]maleonitrile (1), which has pronounced excited‐state charge‐transfer properties, shows a previously unrecognized form of photoisomerization. On electronic excitation (denoted by an asterisk), 1Z*→1Eisomerization takes place by rotation about the C2C3 bond, which takes on single‐bond character due to the charge‐transfer reaction. The isomerization takes place nonadiabatically from the excited‐state (1Z) to the ground‐state (1E) potential‐energy surface in the singlet manifold; 1Zand 1Eare neither thermally inconvertible at ambient temperature (25–30 °C), nor does photoinduced reverse 1E*→1Z(or 1Z*) isomerization occur. Isomers 1Zand 1Eshow very different coordination chemistry towards a ZnIIprecursor. More prominent coordination chemistry is evidenced by a derivative of 1bearing a carboxyl group, namely, N,N′‐dicyanoethenebis(salicylideneimine)dicarboxylic acid (2). Applying 2Zand its photoinduced isomer 2Eas building blocks, we then demonstrate remarkable differences in morphology (sphere‐ and needlelike nanostructure, respectively) of their infinite coordination polymers with ZnII.