H- and J-aggregates of conjugated polymers and oligomers: A theoretical investigation

Excited-state interactions between two oligo-phenylene molecules are evaluated for different intermolecular orientations using singles configuration interaction with a Pariser–Parr–Pople Hamiltonian. As one molecule in a pair of cofacially overlapping molecules is displaced along its axis, an H- to J-aggregate crossover occurs at the slip fraction f0. For intermolecular separations typical of polymer aggregates, f0 initially decreases with oligomer size, but converges in the polymer limit to 0.44 and 0.48 for oligo-p-phenylene (OP)n and oligo-p-phenylene vinylene (OPV)n dimers, respectively. Relative intermolecular rotations are also investigated. Implications for larger aggregates are discussed.