Frenkel Exciton Superexchange, Pair Interactions, and Dispersion Relation:B2u1Naphthalene Crystal

Guest-host-guest exciton exchange (superexchange) is appreciable in the ${}_{}{}^1{}_{}{}^{}B_{2\mathrm{u}}^{}{}_{}{}^{}$ state of a ${\mathrm{C}}_{10}$ ${\mathrm{H}}_8$-${\mathrm{C}}_{10}$ ${\mathrm{D}}_8$ mixed crystal. The experimental resonance pair fine structure in this system has been satisfactorily fitted, resulting in three sets of six pairwise exciton interactions, consistent with all known experimental data. A point multipole expansion, limited to nonoverlapping charge distributions and truncated after the transition-octupole-transition-octupole term, is only consistent with one set, whose values are presented. Using these values, the exciton band structure is completely determined within the restricted Frenkel limit.