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

    Year: 2021

    Journal: Dyes Pigment., Volume 187, MAR

    Authors: Li, Jia-Xin; Xu, Ji-Jun; Luo, Wen-Qi; Jin, Chuan-Ming

    Organizations: National Natural Science Foundation of China [21171053]; Natural Science Foundation of Hubei Province [2015CFC799]; Science and Technology Foundation for Creative Research Group of HBDE [T201311]

    Keywords: Photochromism; Supramolecular chirality; Langmuir-blodgett film; Phenylazoimidazole

    Three non-classical amphiphilic phenylazoimidazole derivatives, viz. 2-methyl 4 (ptolylazo)-1H-imidazole (4-TAIM), 2-methyl-4-(phenylazo)-1H-imidazole (4-PRIM), 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 (pi-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-PRIM, and 4-BPAIM films respectively. Notably, the Ag(I)-coordinated 4-PRIM films show supramolecular chirality, although the azo-imidazole ligand 4-PRIM itself is achiral. This supramolecular chirality was suggested to be due to a cooperative, stereoregular, pi-pi stacking between the neighboring azophenyl imidazolium units, and the orderly interfacial organization with symmetry breaking in some systems.
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