Time-Resolved EPR Study on Singlet-Fission Induced Quintet Generation and Subsequent Triplet Dissociation in TIPS-Phenyl-Tetracene Aggregates

The singlet fission (SF) is expected to be powerful tool for exceeding the theoretical limit of the power conversion efficiency on the organic solar cells. However, little is known on the intermolecular SF mechanism in the solid state. In the present study, we have investigated intermolecular SF in 2-phenyl-6,11-bis(triisopropylsilylethynyl)tetracene (TIPS-Ph-Tc) in frozen solutions using a time-resolved electron paramagnetic resonance measurement at a low temperature. SF-born quintet states (Q) and subsequent dissociations into two triplet states (T + T) were detected for a diluted solute concentration of 10(-4) M in dichloromethane. The microsecond triplet dissociation was found to occur due to the amorphous morphology in the frozen aggregate, suggesting that Q is generated as a trapped state. Furthermore, it was also suggested that the T + T dissociation follows the Q generation due to a T-T repulsion, whose energy were determined by the negative exchange couplings in the triplet pairs, (TT).