LAUSR

Bimolecular equilibria measured the one-electron reduction potentials and triplet free energies (ΔG°T) of oligo(9,9-dihexyl)fluorenes and a polymer with lengths of n = 1–10 and 57 repeat units. Accurate one-electron potentials can be measured electrochemically only for the shorter oligomers. Starting at n = 1 the free energies change rapidly with increasing length and become constant for lengths longer than the delocalization length. Both the reduction potentials and triplet energies can be understood as the sum of a free energy for a fixed polaron and a positional entropy. The positional entropy increases gradually with length beyond the delocalization length due to the possible occupation sites of the charge or the triplet exciton. The results reinforce the view that charges and triplet excitons in conjugated chains exist as polarons and find that positional entropy can replace a popular empirical model of the energetics.