A Molecular Design Principle for Pure-Blue Light-Emitting Polydiarylfluorene with Suppressed Defect Emission by the Side-Chain Steric Hindrance Effect

Functional side chains of light-emitting conjugated polymers (LCPs) play critical roles in the photophysical, electronic, and mechanical performances of the solution-processed polymer light-emitting diodes (PLEDs). Herein, we reported a molecular design principle of polydiarylfluorenes for realizing pure-blue light emission that is introducing functional side chains containing carbazole and amide groups. Resulting from the steric hindrance effect of carbazole groups, the hydrogen bond interactions among the side-chain amide groups were destroyed. As a consequence, both solution-processed films and PLEDs based on such films presented pure-deep-blue emission with the Commission International de L'Eclairage (CIE) coordinates of (0.15, 0.10) and (0.17, 0.14), respectively. Time-resolved transient spectroscopy revealed their similar exciton behaviors in film excited states, and the ultrafast energy transfer occurred within tens of picoseconds. These insights enable us a deeper understanding about the influence of functional side chains on the optoelectronic properties and supply a feasible design strategy for high-performance conjugated polymers.