Stable white light emission from a single organic molecule via intermolecular hydrogen bond to excited-state intermolecular proton transfer

Abstract

It is widely recognized that hybrid (organic/inorganic) light emitting diodes (LEDs) are of concern because they use an organic material instead of rare earth phosphors, but extending their lifetime remains challenging. To construct organic luminescent material with high photoluminescence quantum yield (PLQY), a compound named 1-(4-(tert-butyl)phenyl)-2-(4′-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1′-biphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazole (TPBI-BPI) was synthesized by connect two imidazoles units. The PLQY of TPBI-BPI is 0.97 in acetonitrile. The white light emission (WLE) of TPBI-BPI in ethyl acetate solution containing acetic acid was observed, and a solvent-type organic/inorganic hybrid white LED device based on TPBI-BPI was prepared. The luminance efficiency, external quantum efficiency, correlated color temperature, K, and Ra (color rendering index) of the solvent-type WLED are 21.71 lm/W, 12.76%, 6329, and 83.2 at 39.90 mA, respectively. The Commission Internationale de l´Eclairage coordinate of the solvent-type WLED is (0.3135, 0.3507). In addition, the lifetime (T70) of the device can reach 130 h. This is due to the excited state intermolecular proton transfer between TPBI-BPI and acetic acid in ethyl acetate solution after UV illumination. This enables TPBI-BPI to obtain WLE and makes the WLED spectrally stable due to this process's dissipation of UV energy. This work provides a strategy to extend the lifetime of a hybrid LED.