Effects of Solvent Polarity and Molecular Assembly on Photoisomerization of p-Hydroxyazobenzene Derivative

The reversible photoisomerization behaviors of p-hydroxyazobenzene derivative ((E)-4-((3,5-diethyl-4'-(hexyloxy)-[1,1'-biphenyl]-4-yl)diazenyl)phenol: C6AzOH) in a variety of solvents was investigated. The relatively less polar solvents such as tetrahydrofuran (THF), ethyl acetate, and toluene supported the generation of ~80-90% of the corresponding cis-isomer. Subsequent irradiation with visible light converted the cis-isomer to the original trans-isomer. By contrast, due to fast thermal cis-to-trans isomerization in relatively polar solvents (such as dimethyl sulfoxide (DMSO), N, N-dimethyl formamide (DMF), methanol (MeOH), and dichloromethane), UV-induced trans-to-cis isomerization could not be observed using UV-visible absorption and 1H NMR spectroscopic measurements. Bubble-like aggregates produced in a THF-H2O turbid suspension had crystalline structures and exhibited little light-response according to different wavelengths of light.