Synthesis and photoisomerization of an azobenzene-containing tetrapyrrolic macrocycle

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 331; pp. 66 - 75
• Main Authors: Yamamoto, Taiki, Nakamura, Daichi, Liu, Guanfan, Nishinaka, Kumiko, Tsuda, Akihiko
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01-12-2016; Elsevier BV
• Subjects: Azobenzene; BODIPY; Carbon; Chemical synthesis; Chloroform; Conversion; Crystallography; Distortion; Irradiation; Macrocycle; Magnetic resonance spectroscopy; NMR spectroscopy; Optical properties; Photoisomerization; Porphyrinoide; Studies; Thermal stability; Ultraviolet radiation; BODIPY; Photoisomerization; Porphyrinoide; Azobenzene; Macrocycle
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2015.08.006

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•Synthesis of an azobenzene-containing tetrapyrrolic macrocycle.•Synthesis of an azobenzene-bridged bisBODIPY macrocycle.•Reversible trans–cis photoisomerization of the chromophoric macrocycle.•Highly distorted V-shaped macrocyclic structures revealed by X-ray crystallography.•Higher structural distortion caused by the trans to cis photoisomerization.
The present study reports syntheses, structural and optical properties, and photoisomerization behaviors of a novel azobenzene-containing tetrapyrrolic macrocycle AzP4 and its bis(BF2) core complex (BF2)2AzP4. X-ray crystallographic analyses of trans-AzP4 and trans-(BF2)2AzP4 revealed that the bisdipyrromethene components bridged by sp3 carbon adopt V-shaped conformations. The structural distortion of trans-(BF2)2AzP4, having a sterically congested cavity, is larger than that of AzP4. When the chloroform solutions of AzP4 and (BF2)2AzP4 were exposed to UV light, these compounds brought about photoisomerizations owing to trans→cis conversion of the azobenzene group. In contrast, cis→trans conversion occurred thermally, and was accelerated upon photo-irradiation with visible-light. A DFT calculation of cis-AzP4 indicates that the photoisomerization brings about a large structural distortion of the macrocyclic ring. 1H NMR spectroscopy revealed that the photoisomerizations of AzP4 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)2AzP4 allows higher trans→cis photoconversion, but its thermal stability is lower than that of cis-AzP4.