Viologen as a Colour Modulator in Photochromism of Polyoxomolybdate-Viologen Hybrids

N,N-disubstituted-4,4-bipyridinium (viologen) compounds and polyoxometalates (POMs) are two large groups of photochromic materials. In this work, we studied the photochromic property and colour modulation property of hydrogen bonding POMs-viologen hybrids. Taking the reported (H(2)pipz)(3)[Mo8O27] (1: no viologen containing) and (C14H11N4O)(2)[Mo8O26] (2) as important examples and combining with the two reported POM-viologen crystalline hybrids, we have demonstrated that C14H11N4OCl2 viologen ligands do participate in the coloration process. Moreover, it can also tune the photochromic property of polyoxomolybdates, displaying a colour modulation effect. This work develops a new colour modulation method based on Polyoxomolybdate-Viologen hybrid photochromic materials and may help to improve the performance of the well-known photochromic polyoxomolybdate family.