Aggregation, thermal annealing, and hosting effects on performances of an acridan-based TADF emitter

New derivative acridan and isophthalonitrile (DAcIPN) was designed and synthesized as efficient TADF-type emitter with photoluminescence quantum yield of doped solid-state layer reaching 83%. Tuning of emission and efficiency of TADF emitter was performed by controlling the singlet-triplet energy splitting. Three important effects concerning the solid-state photophysics of TADF emitter was observed and analyzed, providing deep insight on the following new- or opposed-to-established results: (i) the TADF efficiency of DAcIPN in guest-host mixtures is insensitive to the host polarity; (ii) aggregation and (iii) annealing processes were found to respectively reduce and increase the dihedral angle between isophthalonitrile ring and acridan moiety, with strong impacts on the photoluminescence parameters. Thermal annealing of DAcIPN-based systems helps both the diffusion of DAcIPN molecules towards a better phase mixing (disaggregation), and the molecular geometry relaxation towards larger dihedral angles. Organic light-emitting diodes with smaller degree of aggregation of DAcIPN demonstrate outstanding lighting characteristics: brightness of 20700 (at 8 V) and 44900 (at 11 V) cd/m², maximum current, power and external quantum efficiencies of 68 and 63 cd/A, 62 and 33 lm/W, 22.5 and 17.1%, for green and yellow devices respectively.