THROUGH-SPACE AND THROUGH-BOND EFFECTS ON EXCITON INTERACTIONS IN RIGIDLY LINKED DINAPHTHYL MOLECULES

Electronic absorption spectra of a series of dinaphthyl molecules, in which the naphthyl moieties are separated by a rigid polynorbornyl bri dge, together with a corresponding model compound have been measured i n n-hexane and acetonitrile solvents. Resonance (molecular exciton) sp littings of the naphthalene 1A(g) --> 2(1)B3u electronic transition ar e observed and found to be substantially greater than predicted by the usual dipole-dipole model. For the two-bond bridged compound a descri ption of the exciton interaction requires consideration of direct thro ugh-space orbital overlap between naphthalenes. Through-space interchr omophore orbital overlaps in the four-bond and the six-bond bridged co mpounds are negligible, and it is concluded that for these systems a s ignificant contribution by a through-bond interaction (involving the s igma- and sigma-orbitals of the bridge) leads to the efficient deloca lization of the excitation observed. This is the first evidence that e xciton interactions can be enhanced by a through-bond interaction.