Intersystem crossing mechanism of thermally activated delayed fluorescence copper(I) thiolate complex: The roles of exchange coupling and magnetic spin interactions

Abstract

The exchange coupling (J) and magnetic dipole (D) interactions of thermally activated delayed fluorescence copper(I) thiolate complex have been investigated by employing computational chemistry methods. The situation of strict orthogonality of the "hole”–“electron" orbitals with the overlap integral 〈ϕ175α|ϕ175β〉 = 0 leads to small J and excessive triplet T1 population, and is unfavorable to the formation of singlet S1 state via the exchange coupling induced reverse intersystem crossing in the triplet state T1. In magnetic dipole interactions, the mutually perpendicular orbitals provides a significant one-center heavy atomic contribution to the SOC, 〈1φ|hySO|3φ〉 = -41.76 and 〈1φ|hzSO|3φ〉 = −63.14 cm−1, which will enhance the probability of intersystem crossing from the T1 to S1, but system needs to overcome a large intersystem crossing barrier height of 11.05 kcal/mol relative to that of the T1 state at the CAM-B3LYP/def2-TZVP(-f) level. Under magnetic field limit, S1−T0, S1−T+1, and S1−T-1 mixing are all inefficient because the large energy gap between T1 and S1, |2J| » gβB prohibits significant mixing in the triplet state T1, but for the S1/T1 crossing point, the S1−T-1 energy gap is comparable to that of the S1−T0 energy gap, allowing for mixing of S1 with T-1 and T0, |Tz〉 = 56%|1, 0〉 + 20%|1, −1〉 + 16%|0, 0〉.