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Non-photoisomerizable butterfly shaped tetrasubstituted azobenzenes: synthesis and photophysical studies

The trans-azobenzene (AB) substituted derivatives with bulky carbazole (1), phenothiazine (2), and phenyl (3) have been synthesized to understand the effect of steric crowding around the –NN– linkage on the photoisomerization process. The substituents maintain orthogonality to the azobenzene plane and the electronic properties exhibit a combination of individual chromophores. Irradiation of 1 and 2 with various light sources including a 365 nm pen-ray lamp, and a 150 W Xe–Hg lamp, and even exposure to sunlight for a week does not yield the cis isomer revealing the exceptional photostability of the synthesized azobenzene derivatives. These studies suggest that possessing steric crowding around the azo linkage would be a potential strategy to develop photostable azobenzene-based functional materials.