Photochromic and photo-regulated fluorescent coordination polymers derived from thiazolothiazole extended viologen in solid state and polymer film

In this study, we addressed the efforts of controlling the structures of coordination polymers (CPs) for enhanced photochromism by modulating interactions between electron donors (EDs) and acceptors (EAs) or boosting EAs' electron affinity. Two new CPs, [Cd (TTVP)0.5 0.5 (2,6-NDC) (H2O)]& sdot;0.5DMF 2 O)]& sdot;0.5DMF (1) 1 ) and [Cd (TTVP)0.5 0.5 (4,4 '-BPC) '-BPC) (H2O)2]& sdot;0.5H2O 2 O) 2 ]& sdot;0.5H 2 O (2) 2 ) have been successfully synthesized using the thiazolothiazole extended viologen ligand TTVP (TTVP = 2,5-bis(pyridinium-4-yl)thiazolo [5,4-d]thiazole propionate) as an EA and different aromatic carboxylic acids as EDs. Complex 1 features a 3D supramolecular structure with interpenetrating layers with n-pi and pi-pi interactions, while complex 2 adopts a 2D structure with layer stacking through n-pi interactions. Both CPs exhibit notable photochromism via photo-introduced electron transfer (PIET) process, with different ED/EA arrangements (ED-EA-ED-EA for 1 and ED-EA-ED for 2 ) affecting their photoresponse. UV irradiation reveals varying photochromic response rates and color contrasts in the two CPs, highlighting EDs' influential role. Furthermore, both CPs showed a synergistic response of photochromism and photo-controlled fluorescence. Notably, a composite polymer film with reversible photochromic and photo-controlled fluorescence behaviors was fabricated by integrating compound 1 into a styrene ethylene butylene styrene (SEBS) matrix. This study presents a new approach for improving the performance of photochromic materials with potential applications in daily life.