Incorporation of a one-dimensional electron-rich chain in viologen-based coordination polymers for super photochromic properties and improved optical applications in polyvinyl alcohol film

Abstract

A viologen derivative- and a carboxylic acid-based one-dimensional (1D) cocrystal Zn(II) coordination polymer, {[Zn(bcbpy)₂][Zn(sip)Cl]·4H₂O}_n (1, bcbpy = 1,1′-bis(3-carboxybenzyl)-4,4′-bipyridinium, sip = 5-sulfoisophthalate), has been produced solvothermally and structurally characterized. Complex 1 comprises two cationic chains (Chain-1) and one anionic chain (Chain-2) that cross each other and grow into a 3D supramolecular structure through hydrogen bonding interactions. Notably, under UV 365 nm irradiation, 1 showed a noteworthy photochromic transition between colorless and deep blue, which should be attributed to the generation of viologen radicals. Interestingly, it exhibited a two-step coloring phenomenon when heated, with the color changing to yellow and brown at 230 °C and 250 °C, respectively. Furthermore, 1 demonstrated selective gas-chromic behavior toward ethylamine (EA), and it is recoverable by washing with MeCN. Furthermore, 1 can be deposited on filter paper and demonstrates a potential application as an inkless print material. Interestingly, when complex 1 is removed from liquid nitrogen, as the temperature rises from 80 to 290 K, it exhibits a yellow green afterglow. In addition, the production of polyvinyl alcohol (PVA) film, 1-PVA, has made the photochromism of 1 practical in ink-free printing, UV detection, and information anti-counterfeiting, and it is confirmed that the photochromic properties of viologen complex can be improved in PVA medium.