Tuning the emission of carbazole-triazine based emitters through aryl substituents: towards efficient TADF materials

Abstract

Four luminescent donor–acceptor–donor molecules based on carbazole (Cz) and triazine (TRZ) derivatives (DCzTRZAr) were prepared through a nucleophilic aromatic substitution followed by a Suzuki reaction. Photophysical properties, including UV-visible absorbance, photoluminescence, photoluminescence quantum yields (PLQYs) and lifetimes as well as electrochemical properties were obtained to compare the effect of the substituent on the aryl core and to determine if the synthesized molecules exhibited thermally activated delayed fluorescence (TADF). It was observed that the substituents significantly influence the emission wavelength, with electron-withdrawing groups (EWGs) inducing red-shifted emissions. Furthermore, molecules with EWGs resulted in higher PLQYs and longer lifetime, providing insights into the excited-state behaviour. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were performed to predict the photophysical properties and to calculate the energy difference between singlet and triplet states (ΔE_ST). Finally, DCzTRZAr-CF₃ exhibits blue emission and prolonged delayed lifetimes, suggesting its potential use as a TADF emitter.