Probing the Early Dynamics of Singlet Fission in Rubrene Thin Films via Femtosecond Time-Resolved Spectroscopy*

Singlet fission is the photophysical process in which one singlet exciton shares its energy with a neighboring ground-state molecule, resulting in the creation of two triplet excitons. This phenomenon can be beneficial in increasing the quantum yield of photovoltaic devices such as solar panels and organic light-emitting diodes (OLEDs). While the formation and decay of the triplet states have been well explored, measurements available at short times lack resolution. Exploring the dynamics of singlet fission occurring in the first fifteen picoseconds of excitation reveals more about the mechanism of singlet excitons separating into triplet pairs. Rubrene crystals, recognized for their long triplet lifetime, are examined using femtosecond time-resolved spectroscopy to capture these dynamics. Resulting transient absorption spectra and decay kinetics provide insight into the early stages of singlet fission, which heavily influence the overall efficiency of the process. Understanding more about the foundational stages of singlet fission can drive material design development to create higher efficiencies in photovoltaic devices and other technologies.