Discerning Between Excimer and Singlet Fission Sites in TIPS-tetracene using Modulated Magnetic Field Photoluminescence

Magnetic field effects play a key role in the characterisation of organic electronic materials. In particular, the microscopic processes underlying singlet fission and triplet-triplet annihilation have been clarified in recent years, through the observation and subsequent theoretical explanation of magnetic field effects in these processes. Here, we study magnetic field effects on the luminescence of 5,12-Bis((triisopropylsilyl)ethynyl) tetracene: a quintessential material in which both singlet fission and triplet-triplet annihilation occur. By performing highly sensitive modulated-field magneto-photoluminescence experiments, we find magnetic field effect lineshapes of unprecedented detail, allowing a precise characterisation of triplet exciton dynamics. By additionally filtering these magnetic field effects by luminescence wavelength, we can identify the historically elusive excimer state by its unique magnetic field signatures. Finally, we show that a theoretical explanation of these field effects requires a model that explicitly accounts for quantum coherences, which highlights the importance of detailed spin dynamics modelling in understanding magnetic field effects, even at room temperature.