High-Yield Triplet States from Charge-Transfer-Mediated Intersystem Crossing in a Thionated Perylene Dimer

Harvesting triplets with high yields by taking advantage of materials capable of efficient intersystem crossing (ISC) is of great interest. Perylene diimides (PDIs) are classical visible-light-absorbing chromophores widely used to investigate ISC processes through functionalization to weaken the radiative decay pathway. The use of sulfur atoms and the introduction of an orthogonal structure are effective strategies to accelerate ISC processes, which could enhance the spin–orbit coupling (SOC) and simultaneously bring in the charge transfer (CT) interaction in PDI based dimers. Herein, to integrate the advantages of the above two methods, a two-in-one strategy is adopted, and two thionated PDI derivatives (PTCA-S4 and PTCA2-S8) are designed and synthesized. These derivatives effectively combine the capabilities of each method to enhance the triplet efficiency. The incorporation of sulfur atoms improves the SOC constants of PTCA-S4, facilitating the rapid transition from S1 → T3. PTCA2-S8 undergoes spin–orbit charge transfer intersystem crossing (SOCT-ISC) with a relatively high triplet yield (ΦT = 87.4%), as evidenced by the transient absorption measurements. Furthermore, the CT state maintains a balance between CT and charge recombination (CR) rate constants. These results underscore the efficacy of a two-in-one strategy to enhance ISC efficiency in PDI materials.