Synthesis of Solution-Processable Donor-Acceptor Pyranone Dyads for White Organic Light-Emitting Devices

A series of donor-acceptor pyranones (3a-m, 4a-h) were synthesized using alpha-oxo-ketene-S,S-acetal as the synthon for their application as emissive materials for energy-saving organic light-emitting devices (OLEDs). Among them, five pyranones 3f, 3g, 3h, 3m, and 4e exhibited highly bright fluorescence in the solid state and weak or no emission in the solution state. Photophysical analysis of these dyes revealed that only 3f and 3m showed aggregation-induced emission behavior in a THF/water mixture (0-99%) with varying water fractions (f(w)) leading to bright fluorescence covering the entire visible region, while other derivatives 3g, 3h, and 4e did not show any fluorescence signal. The computational studies of the compounds revealed that the longer wavelength absorption originates from HOMO to LUMO electronic excitation. These dyes exhibited good thermal stability with 5% weight loss temperature in the range of 218-347 degrees C. The potential application of the donor-acceptor pyranone dyads was demonstrated by fabrication of solution-processed OLEDs. Remarkably, OLED devices prepared using highly emissive compounds 6-(anthracen-9-yl)-4-(methylthio)-2-oxo-2H-pyran-3-carbonitrile (3m) and 6-(4-methoxyphenyl)-4-(methylthio)-2-oxo-2H-pyran-3-carbonitrile (3f) displayed pure white emission with CIE coordinates of (0.29, 0.31) and (0.32, 0.32), respectively. Additionally, the resultant devices exhibited external quantum efficiencies of 1.9 and 1.2% at 100 cd m(-2), respectively.