Molecular rearrangement at charged states: Intrinsic effects upon photo and electroluminescence

Two luminescent donor-acceptor isomers based on thiophene and benzothiadiazole were designed and synthesized for photophysical property investigations. Their isomeric molecular structures, different photoluminescence, but similar electroluminescence, offer a good platform for in-depth exploration of photoluminescence-electroluminescence relations. The continuous emission color tuning with mono-peak photoluminescence spectra in both solution and film was readily realized. The non-doped OLED device of one isomer shows a low turn-on voltage (2.45 V) with a maximum luminance of 1825 cd/m² and a slight red-shift of electroluminescence (26 nm). In contrast, the other isomer demonstrates a highly red-shifted electroluminescence (53 nm), which was supposed to be intrinsically resulted from the extensively rearranged molecular structures at charged states triggered by the external electronic field during the device operation. These findings based on systematic mechanism analysis, theoretical calculations, and experimental results may provide valuable insight into the optoelectronic property relations especially for the material design of OLEDs.