Most TADF molecule design strategies focus on the minimization the DEST, however, it is observed that the enhancement of the SOC for the T1→S1 transition and the reduced reorganization energy also significantly contribute to the faster 𝑘 *+$& in tBuCz3mTRZ compared to tBuCz3pTRZ, despite their similar ΔEST values. This work demonstrates the importance of the regiochemistry of the donor dendrons on the control of the SOC and reorganization energies, which is a heretofore unexploited strategy that is distinct from the involvement of intermediate triplet states through a non-adiabatic (vibronic) coupling with the lowest singlet charge transfer state. The introduction of tert-butyl groups to carbazole donor dendrons in G1TAZ was reported by Ulanski et al. Dendrimers TR1 and TR2 (Figure ) contain one and two tert-butyl groups on each carbazole unit, respectively, their inclusion was designed to improve the solubility of the dendrimers. Similar to Cz-TRZ, both TR1 (λPL: 398 nm; FPL: 83% in hexane) and TR2