Minimization of Solid-State Solvation and Conformation Disorder Corollaries on Performance of Blue TADF Emitters by Multi-Donor-Acceptor Substitution Engineering

Intramolecular locking and coumarin insertion: a stepwise approach for TADF design

“…Moreover, the theoretical DE ST can be estimated by calculating the difference between this S 1 value and the calculated vertical excitation energy for T 1 , which is also tabulated (Table S2, ESI †). The theoretical DE ST values for both Qx-Ph-DMAC and BQx-Ph-DMAC are considered too large to generate up-conversion from T 1 to S 1 , 20 and thus no TADF emission is expected in this environment. In contrast, the calculated energy gap for ChromPy-Ph-DMAC and DBChromQx-DMAC (0.12 and 0.08 eV, respectively) becomes sufficiently small for rISC and up-conversion to occur (which is observed experimentally, vide infra).…”

“…These trapped triplet excitons can be harvested (though inefficiently) by rISC in both materials, but also by RTP for BQx-Ph-DMAC in which both the S 1 -T 1 and T 2 -T 1 energy gaps are smaller. 20 On the other hand, for ChromPy-Ph-DMAC and especially for DBChromQx-DMAC, vibronic coupling between the 3 LE and 3 CT states (with much smaller DE ST ) enables efficient up-conversion to the singlet state, supporting efficient TADF as the delayed emission mechanism. The improved TADF kinetics of DBChromQx-DMAC are also supported by its smaller experimental DE ST and evidenced by larger k rISC values compared to ChromPy-Ph-DMAC.…”

“…16 A downside of increasing the rigidity of the active material is that this is frequently accompanied by a higher degree of planarity and resulting tendency to aggregate, which is particularly common in D-A TADF compounds. [17][18][19] This aggregation behaviour can be resolved, either by ensuring a near-perpendicular orientation between the D and A to sterically frustrate strong intermolecular p-p-interactions, 20 or by implementing bulky substituents. [21][22][23][24] In this work we demonstrate two parallel rational design strategies to enhance the emission properties of D-A TADF molecules.…”