Explaining Anomalous Thermally Activated Delayed Fluorescence (TADF) Response for a Phenothiazine Derivative through a TD-DFT Approach

Thermally activated delayed Fluorescence (TADF) mechanism can occur by a complicated and fascinating route involving the triplet manifold. Here, we report a computational approach based on Time Dependent Density Functional Theory (TD-DFT) to shed light on the anomalous response of a phenothiazine derivative exhibiting efficient TADF only upon aggregation. The strong red-shifted peak in the photoluminescence spectrum of the molecule dispersed in a non-polar solvent (i.e. cyclohexane) is explained in terms of aggregation of monomers and dimer formation.