Singlet fission in spiroconjugated dimers.

Spiroconjugation results in a unique arrangement of conjugated fragments providing a novel way to chemically connect chromophoric units and control their electronic interaction, which is a key factor for the viability of the singlet fission photophysical reaction. In this study, we computationally explore the possibility of intramolecular singlet fission in spiroconjugated dimers by characterizing the nature of the low-lying excited electronic states, evaluating the magnitude of interstate couplings, describing possible singlet fission mechanisms, and investigating the potential role of low and high frequency vibrational modes in the exciton fission process. The spiro linkage of organic chromophores with the proper excited singlet and triplet energies favors the presence of low-lying charge resonance states, which play a major role in the formation of the triplet pair state. Overall, our results suggest that spiroconjugated dimers are potentially good candidates to efficiently generate independent triplet states through singlet fission.