Photoluminescent Property of Electrochemically Self-Assembled CuSCN/Dye Hybrid Thin Films

Nanostructured hybrid thin films of crystalline CuSCN and fluorescent cationic dyes; Rhodamine B (RB), Nile Blue A (NB) and 4-(N,N-dimethylamino)-4'-(N'-methyl)stilbazolium (DAS) were obtained by electrochemical self-assembly from a single pot containing all the chemical ingredients. Concerted functionalities achieved by the intimate interaction between CuSCN and dye was studied for photoluminescence (PL) behavior between 77 and 298 K. PL from RB and NB was totally quenched when they were hybridized with CuSCN, due to hole transfer from the dye excited state to the valence band of CuSCN, potentially indicating their use as light absorber in solar cells and photodiodes. On the contrary, that of DAS was not quenched despite of its favorable HOMO position for the hole transfer. Crystalline DAS salt with tosylate (DAST) exhibited a strong exciton-phonon coupling to weaken, broaden and red-shift PL at room temperature, so that it inversely is strongly enhanced, sharpened and blue-shifted at 77 K. The PL of the same chromophore in the hybrid thin film, however, shows a slight red-shift and only moderate enhancement at reduced temperature, due to exciton stabilization and energy transfer from CuSCN to DAS luminophore, making it a unique nearly temperature-independent luminescent material.