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 [Mo 8 O 27 ] ( 1 : no viologen containing) and (C 14 H 11 N 4 O) 2 [Mo 8 O 26 ] ( 2 ) as important examples and combining with the two reported POM–viologen crystalline hybrids, we have demonstrated that C 14 H 11 N 4 OCl 2 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.