Two novel Zn(II)-thiazolothiazole extended viologen complexes with photochromism, inkless and erasable printing and photo-modulated luminescence

The insertion of conjugated units between the two pyridine rings of traditional viologens is an effective way to regulate the stimulus response. Herein, the rigid thiazolothiazole extended viologen moiety (TTVP, 2,5-bis (pyridinium-4-yl) thiazolo [5,4-d] thiazole propionate) has been utilized in the preparation of photochromic materials, in which two novel complexes {[Zn (TTVP)0.5 (m-HBTC) (H2O)]·DMF·3H2O}n (1) and [Zn(H2O)6]0.5 (p-BDC)0.5·(TTVP)0.5 (2) (m-H3BTC = 1,2,4-benzenetricarboxylic acid, p-H2BDC = 1,4-benzenedicarboxylic acid), have been synthesized and characterized. Structural analysis exhibits that complex 1 features one-dimensional (1D) chain structure, while complex 2 exists as a discrete monomeric structure. As anticipated, both complexes exhibit reversible photochromic properties under UV irradiation because of electron transfer (ET). More importantly, the photo-controlled luminescent properties and the potential application as inkless and erasable printing media are also explored.