Mechanisms of excitation transfer in multichromophoric systems

The nature of the interactions which promote interchromophore electronic excitation transfer are examined. They are partitioned into direct and relayed components, where direct electronic coupling takes the form of a dipole-dipole interaction at large separations. Factors which modify this interaction at short to intermediate separations are discussed (with particular reference to aromatic polymer systems). The direct interaction is partitioned into coulombic, exchange and penetration terms; the significance of the penetration interaction at close separation (proposed recently for the first time) is elaborated upon here. The relayed interaction involves mediation of all these interactions over lage direct separations via intervening moieties. It is demonstrated, using a model poly(acenaphtylene) dyad as an example, that relayed interactions, mediated via the σ bonds connecting two chromophores, are capable of increasing substantially the rate of electronic excitation transfer.