Organic Light-Emitting Diodes with a White-Emitting Molecule: Emission Mechanism and Device Characteristics

The unique and unprecedented electroluminescence behavior of the white-emitting molecule 3-(1-(4-(4-(2-(2-hydroxyphenyl)-4,5-diphenyl-1H-imidazol-1-yl)phenoxy)phenyl)-4,5-diphenyl-1H-imidazol-2-yl)naphthalen-2-ol (W1), fluorescence emission from which is controlled by the excited-state intramolecular proton transfer (ESIPT) is investigated. W1 is composed of covalently linked blue-and yellow-color emitting ESIPT moieties between which energy transfer is entirely frustrated. It is demonstrated that different emission colors (blue, yellow, and white) can be generated from the identical emitter W1 in organic light-emitting diode (OLED) devices. Charge trapping mechanism is proposed to explain such a unique color-tuned emission from W1. Finally, the device structure to create a color-stable, color reproducible, and simple-structured white organic light-emitting diode (WOLED) using W1 is investigated. The maximum luminance efficiency, power efficiency, and luminance of the WOLED were 3.10 cd A(-1), 2.20 mu m W(-1), 1 092 cd m(-2), respectively. The WOLED shows white-light emission with the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (0.343, 0.291) at a current level of 10 mA cm(-2). The emission color is high stability, with a change of the CIE chromaticity coordinates as small as (0.028, 0.028) when the current level is varied from 10 to 100 mA cm(-2).