Efficient singlet fission in rubicene null aggregates

Abstract

The singlet fission (SF) photovoltaic applications are currently restricted by the limited number of practical SF materials and the underlying SF mechanism in typical molecular aggregates. Null-aggregates are molecular aggregates that exhibit minimal exciton-exciton interactions leading to a monomer-like spectroscopic signature and thus hold some different advantages to bypass extra energy loss and excimer trap issues in conventional H- and J-aggregates. However, it remains unknown if null-aggregates could also contribute to an efficient SF process. In this work, we presented an efficient SF system based on rubicene null aggregates. The comprehensive structural and spectroscopic studies demonstrate that the destructive interference between long-range Coulomb and short-range charge-transfer (CT) couplings lead to the monomer-like optical characteristics of the null aggregates. More importantly, the siginicant CT coupling interactions contribute to an efficient SF process with a SF rate of (1.0 ps)⁻¹ and a triplet yield of 192% in the null aggregates. Our findings not only provide a deep insight into the SF mechanism in the special null aggregates but also offer a robust SF material system with suitable energies, which would open up new avenue for the future molecular design and device applications.