Synthesis and Properties of Photoresponsive Organogels Based on Azobenzene Derivatives

Eighteen azobenzene derivatives, 1a-6a, 1b-6b and 1c-6c, were synthesized and their gelation behaviors were tested. The synthesized azobenzenes readily formed stable gels in many polar or apolar organic solvents. As the representative, the structures of gels from compound 4b and the driving force of the gel formation were investigated by SEM and H-1 NMR. The photoresponse of the gels from compounds 4a-4c was studied and they all showed gel-sol transition under UV light irradiation while sol-gel transition in visible light radiation. Teas parameters of the solvents and gelators were systematically calculated and presented in the Teas plots. The results show that the four gelation behaviors(solution, partial gelation, gelation and precipitation) are located in different regions respectively. In the region of gelation, the distance between the solvent and the gelator reflects the thermal stability of the gel, the farther the distance is, the better the thermal stability of the gel will be.