Supramolecular chirality and photochromism in Langmuir-Blodgett films of fabricated silver-induced phenylazoimidazole derivatives

Abstract

Three non-classical amphiphilic phenylazoimidazole derivatives, viz. 2-methyl-4-(p-tolylazo)-1H-imidazole (4-TAIM), 2-methyl-4-(phenylazo)-1H-imidazole (4-PAIM), and 2-methyl-4-(p-bromophenylazo)-1H-imidazole (4-BPAIM), were synthesized herein and their in-situ molecular assemblies upon coordination with AgNO3 in the monolayer at the air/water interface were investigated. The surface pressure-area (π-A) isotherms showed that all these compounds could be spread on the surface of the AgNO3 solution, although they have no alkyl chains. The transferred multilayers were arranged in an H-aggregate and showed good photochromic properties, with 40%, 50%, and 20% trans-to-cis photoisomerization in the photo-stationary state for 4-TAIM, 4-PAIM, and 4-BPAIM films respectively. Notably, the Ag(I)-coordinated 4-PAIM films show supramolecular chirality, although the azo-imidazole ligand 4-PAIM itself is achiral. This supramolecular chirality was suggested to be due to a cooperative, stereoregular, π-π stacking between the neighboring azophenyl imidazolium units, and the orderly interfacial organization with symmetry breaking in some systems.