INTRAMOLECULAR ELECTRONIC-ENERGY TRANSFER BETWEEN RIGIDLY LINKED NAPHTHALENE AND ANTHRACENE CHROMOPHORES

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) b icyclo-[2.2.0]hexane bridge, six sigma-bonds in length, is measured to be 2.9 x 10(10) s-(1) (n-hexane). EET between the lowest-energy napht halene (1)L(b) and anthracene (1)L(a) states (via a direct Coulombic m echanism) is forbidden in this molecule because of the orthogonality o f donor and acceptor transition dipoles. EET involving a Coulombic int eraction between the naphthalene (1)L(b) and the nonfluorescent anthra cene (1)L(b) 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 dom inant role. The significance of these results to EET in aromatic polym ers and other multichromophoric systems is discussed.