Intramolecular electronic energy transfer between rigidly linked naphthalene and anthracene chromophores

Abstract

The rate of intramolecular singlet-singlet electronic energy transfer (EET) between naphthalene and anthracene chromophores that are held in a well-defined orientation and separation by a rigid bis(norbornyl)bicyclo-[2.2.0]hexane bridge, six σ-bonds in length, is measured to be 2.9 × 1010 s-1 (n-hexane). EET between the lowest-energy naphthalene 1Lb and anthracene 1La states (via a direct Coulombic mechanism) is forbidden in this molecule because of the orthogonality of donor and acceptor transition dipoles. EET involving a Coulombic interaction between the naphthalene 1Lb and the nonfluorescent anthracene 1Lb electronic states is also considered. Although Coulombic EET is vibronically allowed, to account for the high measured rate, it is proposed that relayed mechanisms, involving the bridge, play a dominant role. The significance of these results to EET in aromatic polymers and other multichromophoric systems is discussed. © 1993 American Chemical Society.