Achieving the Reverse Intersystem Crossing in Chalcone Based Donor‐Acceptor System through Down‐Conversion of Triplet Exciton

Abstract

In recent years, understanding the mechanism of thermally activated delayed fluorescence (TADF) has become the primary choice for designing high‐efficiency, low‐cost, metal‐free organic light emitting diodes (OLEDs). Herein, we propose a strategically designed chalcone based donor‐acceptor system, where intensification of delayed fluorescence with decrease in temperature (300K to 100K) is observed; the theoretical investigations of electronic states and orbital characters uncovered a new cold rISC pathway in donor‐acceptor system, where rISC occurs through the down‐conversation of higher triplet exciton (from T3) to lowest singlet state (S1), having negative energy splitting, thus no thermal energy is required. The comprehensive research described herein might open‐up new avenues in donor‐acceptor system over the conventional up‐convention of triplet exciton and demonstrates that not necessarily all delayed fluorescence are thermally activated (TADF).