Controlling chromophore assembly and coupling via carbon nanohoops enables singlet fission at interchromophore distances up to 16 Å.

Singlet fission, a process that converts a photoexcited singlet exciton into two triplet excitons via a triplet pair (TT) intermediate state, holds important potential for enhancing the efficiency of solar cells. The interchromophore distance plays a critical role in dictating the fate of TT states, with larger separations being favourable for TT decorrelation. However, efficient TT generation through intermolecular singlet fission has thus far been limited to chromophore assemblies with nearest-neighbour distances below 5.6 Å because interchromophore coupling is inherently governed by weak van der Waals forces. Here we modulate interchromophore distances by simultaneously engineering through-space and through-bond charge-transfer interactions. Utilizing this strategy with the carbon nanohoop motif, we demonstrate that ultrafast singlet fission (<4 ps) remains active even when the distance between chromophores is ∼16 Å at its shortest point. This finding underscores that the van der Waals limit is no longer a fundamental design constraint in the search for new singlet fission materials.