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

Excited-state interactions between two oligo-phenylene molecules are evalua ted for different intermolecular orientations using singles configuration i nteraction 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 f(0). For intermolecular separations typical of polymer aggregates, f(0) initially decreases with ol igomer 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, respec tively. Relative intermolecular rotations are also investigated. Implicatio ns for larger aggregates are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.