Photo-induced fiber-vesicle morphological change in an organogel based on an azophenyl hydrazide derivative

A new low molecular mass organic gelator (LMOG) bearing hydrazide and azobenzene groups, namely N-(3,4,5-octanoxyphenyl)-N'-4-[(4-hydroxyphenyl)azophenyl] benzohydrazide (BNB-t8), was designed and synthesized. The organogelator has shown great ability to gel a variety of organic solvents to form stable organogels with a critical gelation concentration as low as 0.5 mg mL(-1). Xerogels from chloroform exhibited entangled and dense fibrous aggregates with diameters of 50-60 nm. The organogel showed photoinduced gel-to-precipitate transition under the irradiation by 365 nm UV-light, which was attributed to trans-BNB-t8 to cis-BNB-t8 photoisomerization. The trans-cis isomerization in BNB-t8 gels further caused the morphological change from fibers to vesicles at the supramolecular level.