Thermally activated delayed fluorescence

Thermally activated delayed fluorescence (TADF) has recently attracted much attention due to the possibility of exploiting it for efficient triplet harvesting, that is, assuring a radiative relaxation of triplet excitons. The primary application area is organic light-emitting diodes (OLEDs), but TADF materials are also promising for such technologies as sensors, photocatalysis, and bioimaging. The basic harvesting mechanism is based on a thermally induced upconversion from the lowest-lying triplet to the lowest-lying excited singlet state; therefore, its kinetics depends on the singlet-triplet energy gap. The actual mechanism turned out to be more complicated, and the TADF rates depend on such effects as the mixing of charge transfer and local excitations, molecular vibrations, environmental polarization, and energy transfer. This chapter will review the underlying theory of TADF and the applications of molecular modeling methods to study and design TADF materials.