Alicycloimide substitution strategy for realizing solution-Processable small molecules material with thermally activated delayed fluorescence

Abstract

Highly efficient solution-processable emitters, especially small molecules, are greatly desired to develop low-cost and low-energy-consumption organic light-emitting diodes (s-OLEDs). A recently developed class of potentially metal-free emitters, thermally activated delayed fluorescence (TADF) materials, are promising candidates, but solution-processable TADF materials are not well investigated. In this study, TADF molecules with or without HHPI unit were synthesized, named PTC-HDA and PTCP, respectively. All of them show TADF properties. The introduction of HHPI significantly enhanced thermo-stability and luminescence property with high photoluminescence quantum yield (Φ_PLQY) from 18.7 % to 48.3 %. Glass transition temperature (T_g) and decomposition temperature (T5% d) increased from 135 °C and 477 °C to 177 °C and 586 °C. PTCP show obvious double emission at 452 nm and 561 nm, while the emission at 452 nm is disappeared for PTC-HDA. HHPI unit enhance the film-forming properties of PTC-HDA with roughness of 0.302 compared with roughness of 0.524 for PTCP, even after one week stay the same as before. In the application to OLEDs preparing through spin-coating process, the high external quantum efficiency (ηmax EQE) of 11.90 % and low efficiency roll-off (1.7 % at 100 lm cm⁻² and 18.8 % at 1000 lm cm⁻²) for PTC-HDA were achieved. Which is significantly improved due to HHPI unit compared with PTCP (ηmax EQE = 7.85 %, efficiency off 7.2 % at 100 lm cm⁻² and 23.3 % at 1000 lm cm⁻²). This work demonstrates the validity of HHPI substitution and paves a pathway for straightforward realization of solution-processable efficient TADF emitters.