Intermolecular charge transfer and solid-state solvent effect synergistically induce near-infrared thermally activated delay fluorescence in the guest–host system

Abstract

The host matrix is an important means to tune emission color and improve luminescence efficiency of near-infrared (NIR) thermally activated delay fluorescence (TADF) light-emitting diodes. However, the mechanism of NIR TADF of the guest–host systems is still unclear. Namely, there is a controversy on whether the formation of J-aggregation, solid-state solvent effect, molecular polarization or intermolecular charge transfer (CT) is responsible for the NIR TADF. Here, the morphologies, geometrical and electronic structures, and photophysical properties are explored by combining molecular dynamics simulation, density functional theory and thermal vibration correlation function theory for the guest–host (TPAAP: TPBi) films with different concentrations. It is found that the red TADF is generated largely by the solid-state solvent effect in the low 1 wt% doped film while the NIR TADF is attributed to the synergistic effect of solid-state solvent and guest–guest intermolecular CT in the high 20 wt% film. These findings provide a deeper understanding of the mechanism of NIR-TADF of the guest–host systems.