Multistimuli-Responsive Fluorescent Switches Based on Reversible Decomposition and Regeneration of charge-transfer Complexes

Charge-transfer (CT) complexes of 4,4'-bis(9H-carbazol-9-yl)-1,1'-biphenyl (CBP) and three acceptors emitted cyan, green, and orange fluorescence, and lower LUMO energy levels of the acceptors promoted longer emission wavelengths. Moreover, they could reversibly convert their luminescent colors under force and then fuming by chlorinated hydrocarbon solvents. Amazingly, acetonitrile vapor annealing might decompose CT complexes to form a pure CBP crystalline phase, which induced sharp changes in the fluorescence colors. As a result, the largest emission shift was more than 220 nm. CT complexes could also be formed through pressing a mixture of a donor and acceptor, and the emission color gradually changed from blue to cyan, green, white, yellow, orange, and even red with extended grinding time, realizing a full color luminescence in the visible light region. Due to their excellent stimuli-responsive behaviors, anticounterfeiting papers with two fluorescent colors have been constructed. Moreover, the fluorescence colors of papers could be reversibly transformed under solvent annealing treatment. High-resolution patterns in both papers might be written by a stylus printer and be erased by solvent fuming with high reversibility.