Synthesis and photoisomerization of an azobenzene-containing tetrapyrrolic macrocycle

The present study reports syntheses, structural and optical properties, and photoisomerization behaviors of a novel azobenzene-containing tetrapyrrolic macrocycle AzP(4) and its bis(BF2) core complex (BF2)(2)AzP(4). X-ray crystallographic analyses of trans-AzP(4) and trans-(BF2)(2)AzP(4) revealed that the bisdipyrromethene components bridged by spa carbon adopt V-shaped conformations. The structural distortion of trans-(BF2)(2)AzP(4), having a sterically congested cavity, is larger than that of AzP(4). When the chloroform solutions of AzP(4) and (BF2)(2)AzP(4) were exposed to UV light, these compounds brought about photoisorrierizations owing to trans cis conversion of the azobenzene group. In contrast, cis-4 trans conversion occurred thermally, and was accelerated upon photo-irradiation with visible-light. A DFT calculation of cis-AzP(4) indicates that the photoisomerization brings about a large structural distortion of the macrocyclic ring. H-1 NMR spectroscopy revealed that the photoisomerizations of AzP(4) with UV and visible light turns on and off the-rotation and/or inversion of its gem-dimethyl groups inside and outside of the macrocyclic ring. We further found that (BF2)(2)AzP(4) allows higher trans cis photoconversion, but its thermal stability is lower than that of cis-AzP(4). (C) 2015 Elsevier B.V. All rights reserved.