Energy splitting between triplet and singlet exciplex states determined with E-type delayed fluorescence

In the redox system with N,N-diethylaniline as electron donor and 1,4-dicyanobenzene as electron acceptor the singlet and triplet exciplex states in the nonpolar solvent methylcyclohexane are almost degenerate. The lowest excited state is the triplet exciplex state from which the singlet exciplex state is populated in a fast endothermic reaction. The energy splitting has been determined experimentally as ΔE ≈ 0.1 eV via E-type delayed fluorescence.