Side-Chain Polarity-Dependent Photoluminescence and Deep Blue Electroluminescence in Fluorene-Based Conjugated Polymer Networks

The development of solution-processable deep blue electroluminescent materials has recently attracted considerable interest in organic light-emitting diode (OLED) research. Here, we report two solution-processable, highly fluorescent, and wide band gap conjugated polymer networks (CPNs) consisting of triazine and fluorene. Two different side chains, alkyl and ethylene glycol, are introduced into the polymer backbone to investigate the effect of side-chain polarity on the fluorescence and electroluminescence properties of the polymer. The thermal, photophysical, and self-assembly properties of the polymer were studied in detail, showing high thermal stability, side-chain polarity-dependent self-assembly, and fluorescence properties in the solid state. The polymer network with an alkyl side chain shows a deep blue color, whereas the ethylene glycol side chain displays a green color. Using these polymer networks, one can create fluorescence patterns of blue and green using UV light. OLEDs based on FCPN2 with an ethylene glycol chain show a maximum quantum efficiency (EQE) of 2.7%, which is much higher than the 0.5% displayed by FCPN1 with an alkyl side chain. FCPN2 exhibits a maximum brightness of 1458 cd/m2 and a maximum current efficiency of 1.2 cd/A with deep blue emission. These findings underscore the potential of side-chain polarity to modify the fluorescence and improve the electroluminescence performance of conjugated polymer-based blue OLED devices.