High-Yield Triplet\nStates from Charge-Transfer-Mediated\nIntersystem Crossing in a Thionated Perylene Dimer

Harvesting triplets with high yields by taking advantage\nof materials\ncapable of efficient intersystem crossing (ISC) is of great interest.\nPerylene diimides (PDIs) are classical visible-light-absorbing chromophores\nwidely used to investigate ISC processes through functionalization\nto weaken the radiative decay pathway. The use of sulfur atoms and\nthe introduction of an orthogonal structure are effective strategies\nto accelerate ISC processes, which could enhance the spin–orbit\ncoupling (SOC) and simultaneously bring in the charge transfer (CT)\ninteraction in PDI based dimers. Herein, to integrate the advantages\nof the above two methods, a two-in-one strategy is adopted, and two\nthionated PDI derivatives (<b>PTCA-S4</b> and <b>PTCA2-S8</b>) are designed and synthesized. These derivatives effectively combine\nthe capabilities of each method to enhance the triplet efficiency.\nThe incorporation of sulfur atoms improves the SOC constants of <b>PTCA-S4</b>, facilitating the rapid transition from S<sub>1</sub> → T<sub>3</sub>. <b>PTCA2-S8</b> undergoes spin–orbit\ncharge transfer intersystem crossing (SOCT-ISC) with a relatively\nhigh triplet yield (<i>Φ</i><sub>T</sub> = 87.4%),\nas evidenced by the transient absorption measurements. Furthermore,\nthe CT state maintains a balance between CT and charge recombination\n(CR) rate constants. These results underscore the efficacy of a two-in-one\nstrategy to enhance ISC efficiency in PDI materials.