Intersystem Crossing Rates of Isolated Fullerenes: Theoretical Calculations

Although the triplet states of fullerenes have prosperous applications, it remains unclear how the structural parameters of singlet and triplet states control the intersystem crossing (ISC) rates. Here, electronic structure calculations (reorganization energy, driving force, and spin-orbit coupling) and a rate theory (Marcus formula) are employed to quantitatively predict the ISC rates of isolated fullerenes C_n (n = 60-110). The results demonstrate that the driving force is not the only factor to predict the ISC rates. For instance, although C₈₀, C₈₂, and C₁₁₀ have the favorable driving force, the ISC rates are close to zero because of small spin obit couplings, whereas small ISC rates of C₉₆ and C₁₀₀ result from quite small reorganization energies. Meanwhile, in addition to well-known C₆₀ and C₇₀, C₉₂ possesses good ISC property with obviously large ISC rate. C₉₂ also has a higher triplet-state energy than singlet-state oxygen energy; it may thus have a good photoactive property.