Intra- and inter-molecular singlet fission in covalently linked dimers
Electronic factors controlling singlet fission (SF) rates are investigated in four-chromophore model systems comprising two covalently linked dimers of tetracene. By using adiabatic framework and wave-function analysis tools, we show that the lowest singlet multi-exciton states are localized on the individual molecules. The inter-molecular ME states, in which the triplet excitons reside on separate moieties, are higher in energy and are not accessible from the lowest singlet excitonic state. Although the electronic states from excitonic/charge-resonance band are delocalized over the four chromohores, the calculations suggest that the essential electronic properties controlling the rates of SF depend largely on the electronic properties of the individual covalently linked chromohores, owing to the strong through-bond couplings.