Through-Bond and Through-Space Coupling in Photoinduced Electron and Energy Transfer:  An ab Initio and Semiempirical Study

Abstract

Ab initio and semiempirical calculations of transfer integrals for electron transfer and energy transfer have been carried out on rigidly linked norbornane-bridged naphthalene dimers to gain insight into the relative importance of through-bond and through-space interactions on photoinduced energy and electron transfer processes. In the absence of direct through-space orbital overlap between the naphthalene moieties, throughbond interaction involving the linking polynorbornane bridge is found to significantly enhance the transfer integrals for electron transfer and triplet-triplet energy transfer. For singlet-singlet energy transfer direct through-space Coulombic interaction between the naphthalene moieties is non-negligible at the separations considered and acts to reinforce the through-bond interaction. The relationship between electron and energy transfer processes and the application of these results to the interpretation of recent experimental data are discussed.

Excitonic couplings and electronic coherence in bridged naphthalene dimers

“…The exciton model completely breaks down for DN-2, which shows a strong electronic coherence between chromophores. The conclusion of Scholes et al (39)(40)(41) that the direct through-space orbital overlaps dominate the absorption spectroscopy only for DN-2 is confirmed by our analysis.…”

“…1) (38)(39)(40)(41). These molecules may be regarded as naphthalene dimers where pairs of naphthalene chromophores are held at fixed distances and orientations by a rigid polynorbornyl-type bridge of variable length (two, four, or six bonds, respectively).…”

“…These molecules may be regarded as naphthalene dimers where pairs of naphthalene chromophores are held at fixed distances and orientations by a rigid polynorbornyl-type bridge of variable length (two, four, or six bonds, respectively). The UV-spectra and radiative decay rates of these dimers have been measured (39)(40)(41) and interpreted by using a simple exciton model (42). Within this model, each excited state of the monomer generates two states in the dimer.…”

“…The estimated splitting by using the exciton model was found to be very small compared with the observed value. This discrepancy was attributed to the through-bond interaction mechanism (39)(40)(41). The exciton model (42) is based on the assumption that the interaction between chromophores is purely electrostatic and could be approximated by dipole-dipole coupling.…”

Deactivation of Excited States in Nanostructures Containing Cu-Porphyrin Subunit

“…In addition, for a set of porphyrin hybrid dimers, PET rate constants are essentially influenced by the spacer nature (electronic properties of chemical bond, the energy of spacer excited states, geometry and flexibility) as well as the additional coordination of porphyrin central metal ion by various extra-ligands. In the result, the interplay of all these factors determines the possible pathways and mechanisms of the PET in the given chemical dimer (theoretically considered as sequential "through-bond" or "throughspace" mechanisms, [46][47][48][49] superexchange coupling through the bridge. [50,51] Nevertheless, in comparison with multiporphyrin arrays involving subunits with diamagnetic metal ions (discussed above), the photochemistry of hybrid nanoassemblies having tetrapyrrolic counterparts with central paramagnetic metal ions, for instance Cu(II), is rather complex because of presence of unpaired d-electron in central metal.…”