Photoresponsive two-component organogelators based on trisphenylisoxazolylbenzene

Photochromic tris(phenylisoxazolyl)benzene 1 and bispyridine derivatives 2a-e were mixed in a certain ratio to generate stable gels in benzyl alcohol, 4-methoxybenzyl alcohol, and aniline. Supramolecular assembly of 1 in solution was confirmed by H-1 NMR study. The T-gel value was saturated in a 2:3 ratio of 1 and 2c. The intermolecular hydrogen bonds OH center dot center dot center dot N and salt bridge O-center dot center dot center dot H-N+ between 1 and 2c coexisted evidently, and these hydrogen bonds contributed to the stabilization of the gel networks. The lengths of alkyl chains of 2a-e governed the stabilities of the gels. The gel formations were driven by the morphological transition of 1 before and after the addition of 2a-e. Mixtures of 1 and 2a-e led to the well developed fibrillar networks, generating a lot of voids that are responsible for immobilizing solvent molecules. When the benzyl alcohol gel was irradiated at 360 nm, the gel turned to the sol. The sol was reversed to the gel by warming. This gel-to-sol phase transition was completely reversible.