Diarylfluorene Flexible Pendant Functionalization of Polystyrene for Efficient and Stable Deep-Blue Polymer Light-Emitting Diodes

Intermolecular aggregation and phase transition are exacerbated by enhancing the free motion of small molecules in the solid state upon an external active stimulus, which is negative to the device performance and stability of deep-blue organic light-emitting diodes (OLEDs). Herein, we proposed a convenient and simple "flexible"-pendant-functionalization strategy to obtain a polystyrene (PS) derivative (PS-MC8TPA) with an excellent stable morphology and efficient deep-blue emission for polymer light-emitting diodes (PLEDs), compared to that of small molecular MC8TPA, even after thermal treatment at 180 °C in air. Meanwhile, the dense and flexible interchain entanglement not only can induce efficient dispersion of MC8TPA molecules in this polymeric system, endowing PS-MC8TPA with stable single-chromophore emission behavior without obvious intermolecular aggregation in the solid state, but also avoid the permeation of O2 and H2O under thermal annealing and aging for 2 days to show a stable deep-blue emission. More interestingly, significantly different from the device efficiency of MC8TPA that has a severe drop after thermal annealing, the device based on a PS-MC8TPA-annealed film presents a relatively high maximum current efficiency (CE: 1.15 cd/A), associated with a stable and efficient deep-blue emission (CIE: (0.18, 0.09)) of its annealed film. These abovementioned results confirmed the effectiveness of our flexible-pendant-functionalization strategy to prepare an efficient and a stable emitter for optoelectronic devices.