The relationship between molecular structure and photophysical properties of a range of boron-based TADF molecules were investigated to provide a clear approach to the structure-performance relation. Torsion angles, excited state energy alignments, singlet-triplet energy gaps, particle-hole orbital overlap extent and spin orbit coupling for reverse intersystem crossing processes were utilized.
Abstract
Thermally activated delayed fluorescence (TADF) materials have shown great potential in the design of organic metal-free optoelectronic devices and materials and, therefore, are the subject of intense investigations. This contribution presents the effects of various parameters on the photophysical properties of a series of boron-based TADF emitters. These include torsion angle, the changes in the electronic density, energy gap between the first excited singlet (S1) and the first excited triplet states (T1), oscillator strength (f) and spin-orbit coupling (SOC). Through a comprehensive structural analysis, we first show the most favorable conformation of the ground state of donor (D) and acceptor (A) moieties that are popular in TADF emitters. Further, the properties of the excited state manifolds are obtained with Tamm-Dancoff Approximation (TDA), thus rationalizing their optical and photophysical properties. Globally, our results settle the basis for the rationalization of the effects of different parameters on reverse intersystem crossing (RISC) probabilities, which is the rate-limiting step for TADF, thus favoring the rational design of novel highly efficient TADF materials with strong triplet exciton harvesting.