Alkyl-chain branched effect on the aggregation and photophysical behavior of polydiarylfluorenes toward stable deep-blue electroluminescence and efficient amplified spontaneous emission

The control of the condensed superstructure of light-emitting conjugated polymers (LCPs) is a crucial factor to obtain high performance and stable organic optoelectronic devices. Side-chain engineering strategy is an effective platform to tune inter chain aggregation and photophysical behaviour of LCPs. Herein, we systematically investigated the alkyl-chain branched effecton the conformational transition and photophysical behaviour of polydiarylfluorenes toward efficient blue optoelectronic devices. The branched side chain will improve materials solubility to inhibit interchain aggregation in solution according to DLS and optical analysis, which is useful to obtain high quality film. Therefore, our branched PEODPF, POYDPF pristine film present high luminance efficiency of 36.1% and 39.6%, enhanced about 20% relative to that of PODPF. Compared to the liner-type sides’ chain, these branched chains also suppress chain planarization and improve film morphological stability effectively. Interestingly, the branched polymer also had excellent stable amplified spontaneous emission (ASE) behaviour with low threshold (4.72 μJ/cm²) and a center peak of 465 nm, even thermal annealing at 220 °C in the air atmosphere. Therefore, side-chain branched strategy for LCPs is an effective means to control interchain aggregation, film morphology and photophysical property of LCPs.