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*-->1E isomerization 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; 1Z and 1E are neither thermally inconvertible at ambient temperature (25-30 degrees C), nor does photoinduced reverse 1E*-->1Z (or 1Z*) isomerization occur. Isomers 1Z and 1E show very different coordination chemistry towards a Zn(II) precursor. More prominent coordination chemistry is evidenced by a derivative of 1 bearing a carboxyl group, namely, N,N'-dicyanoethenebis(salicylideneimine)dicarboxylic acid (2). Applying 2Z and its photoinduced isomer 2E as building blocks, we then demonstrate remarkable differences in morphology (sphere- and needlelike nanostructure, respectively) of their infinite coordination polymers with Zn(II).
Lin
Chun-Wei
CW
Department of Chemistry, National Taiwan University, Taipei, Taiwan.
Chou
Pi-Tai
PT
Liao
Yong-Hong
YH
Lin
Ying-Chih
YC
Chen
Ching-Ting
CT
Chen
Yu-Chun
YC
Lai
Chin-Hung
CH
Chen
Bo-So
BS
Liu
Yi-Hung
YH
Wang
Chih-Chieh
CC
Ho
Mei-Lin
ML