Multifunctional thermally activated delayed fluorescence emitter for both doped and non-doped organic light emitting diodes

Developing efficient smart materials that display mechanochromic luminescence (MCL) and thermally activated delayed fluorescence (TADF) remains a formidable challenge. Herein, we designed and synthesized a multifunctional emitter, 2BPy-mTC, where benzoyl pyridyl (2BPy) acts as an acceptor and 3,6-di-tert-butyl-9H-carbazole (TC) acts as a donor. 2BPy-mTC exhibits blue emission with λ_max of 456 nm in pristine form and emission shifted to green with λ_max of 495 nm upon grinding. Interestingly, when fumed with CH₂Cl₂, the emission reverts to deep blue at λ_max of 440 nm. 2BPy-mTC possesses a ΔE_ST of 0.20 eV in neat film and 0.11 eV in doped film (5 wt% 2BPy-mTC: mCBP) and exhibits a PLQY of 42 % in neat film and 59 % in doped film. The transient photoluminescence (PL) decay curves show a delayed lifetime of 110.3 μs for the neat film and 192.9 μs for the doped film and confirm the TADF property in both doped and non-doped film. It shows an EQE_max of 16.3 % in doped device with an emission maximum of 484 nm. Conversely, it retains the EQE_max of 13.8 % in non-doped device with a slight red shift in the emission maximum (496 nm). This discovery opens a new avenue for designing multifunctional emitters with improved EL performance.