Two New Photochromic Coordination Compounds with Thiazolothiazole Extended Viologen and Two Different Auxiliary Ligands

A new thiazolothiazole extended viologen ligand (TTVP, 2,5-bis(pyridinium-4-yl)thiazolo[5,4-d]thiazole propionate) was synthesized. Through mixed-ligand synthesis, two novel photochromic compounds, [Zn(4,4′-bpy)(TTVP)]·(NO3)2·4H2O (1) and [Zn(Hbtc)(TTVP)0.5] (2) (4,4′-bpy = 4,4′-bipyridine, H3btc = benzenetricarboxylic acid), were obtained by assembly of a photoactive TTVP ligand and auxiliary ligands with different coordinating atoms (N/O). 1 possesses an eight-fold dia structure with two kinds of coordinating atoms (N/O), while 2 has a two-dimensional layer structure with entirely O coordination. TTVP and compounds 1 and 2 are all photochromic, but the distance between electron donors (Ocarboxylate) and acceptors (Npyridinium) in one TTVP is beneficial to photochromism in 2 but not in 1, and a quicker response is indeed observed in 2 due to that short distance.