Enhancing Triplet Excitons Lifetime Through Controlled Intermolecular Interactions

Singlet fission (SF) is a process in which a singlet exciton is converted into two triplet excitons, significantly enhancing charge generation in organic solar cells. It has been shown that the rate of SF and the lifetime of the generated triplet excitons strongly depend on the molecular arrangement. In this work, a cofacial orientation of pentacene molecules is achieved by embedding organic linkers containing pentacene in a surface-anchored metal–organic framework. Transient absorption spectroscopy and a quantum mechanical analysis are used to analyze the exciton dynamics in a broad spectral range from near-ultraviolet to near-infrared. The observed spectra indicate that a singlet excited state generates a correlated triplet pair within a few picoseconds. Subsequent dynamics show the formation of long-lived excitons (39 $\mu$s) with triplet character. This exceeds by far the observed lifetime of triplet excitons generated in pentacene thin films and may enhance triplet exciton harvesting capabilities in photovoltaic cells.