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 Delta E approximate to 0.1 eV via E-type delayed fluorescence. (C) 2008 Elsevier B. V. All rights reserved.