Photochromic properties of five complexes derived from 1, 3, 5-benzenetricarboxylic acid and 1-(2-carboxyethyl)-4,4′-bipyridinium bromide

Non-photochromic and photochromic complexes [Ni-1.5(CBbpy)(H2O)(7)]center dot(BTC)center dot 5 center dot.5H(2)O (1), {[Co (CBbpy)(2)(H2O)(2)]center dot(HBTC)center dot 8H(2)O}(n) (2), {[MnNa(CBbpy)(BTC)(H2O)(3)]center dot H2O}(n) (3), {[Zn-3(CBbpy)(2)(BTC)(2)(H2O)]center dot H2O}(n) (4), {[Cd(CBbpy)(HBTC)(H2O)]center dot H2O}(n) (5) based on the bipyridinium-based ligand 1-(2-carboxyethyl)-4,4' -bipyridinium bromide (HCBbpyBr) and 1,3,5-benzenetricarboxylic acid (H3BTC) have been successfully obtained by tuning different metal ions. Although five complexes contain the same bipyridinium ligand, only 3-5 possess reversible photochromic behavior. Unfortunately, 1 and 2 exhibit non-photochromic action when exposed to UV light for approximately 2 h. EPR spectra verify that photochromic course of 3-5 is derived from the formation of CBbpy radicals by photo-induced electron transfer after irradiation. The effect of diverse metal ions on the structure and photochromic action of the five complexes has been discussed.