Disclosing the Impact of Local Host Effects on TADF Dynamics

Abstract

Donor-acceptor (D-A) type thermally activated delayed fluorescence (TADF), a key technology of proposed Gen3 organic light emitting diodes (OLEDs), is highly sensitive to the rigidity and polarity of the local environment. Specifically, the torsional flexibility of the D-A dihedral angle and the dipole character of charge transfer states give rise to a distribution of TADF dynamics across the emitter ensemble. Here, we employ single molecule spectroscopy to access the photophysics of individual emitters, thus overcoming the limitations of ensemble averaging. Using photon correlation measurements and locally resolved spectral data from single D-A type TADF molecules embedded in host materials of different polarity and rigidity, we derive host-dependent characteristics and distributions in the TADF dynamics. These are directly linked to local conformational freedom and dielectric properties, offering new insight into host-emitter interactions and enabling rational design strategies for optimized host-emitter combinations in OLED applications.