Rate expressions for excitation transfer. III. An ab initio study of electronic factors in excitation transfer and exciton resonance interactions

Abstract

A detailed theory for electronic aspects of electronic excitation (energy) transfer (EET) for sandwich dimers was derived in paper II of this series [J. Chem. Phys. 101, 10 521 (1994)]. In II, the electronic transfer matrix element for EET was evaluated, then simplified to various levels of approximation. The results of ab initio molecular orbital calculations on an ethene sandwich dimer are reported here in order to test and quantify the theory of II. The calculations were undertaken using a STO-6G basis set and localized molecular orbitals, with separations of 4, 5, and 6 Å between the molecules. It is demonstrated that the important electronic factors contributing to EET are the Coulombic interaction (for direct singlet–singlet transfer) and, for both singlet–singlet and triplet–triplet EET, orbital overlap-dependent interactions. The dominant orbital overlap-dependent terms arise from through-configuration interaction, which involves successive one-electron transfers mediated via bridging ionic configurations, first presented in II. The results confirm that the Dexter-type exchange interaction is small in comparison.

A simplified approach for the coupling of excitation energy transfer

“…The first two come from the polarization effect and Dexter exchange effect [33]: the transition dipoles localized at A but computed in the presence of B are higher than transition dipoles computed without the presence of B; the Dexter part which is taken into account by our method contributes to H 14 with the opposite sign of the Coulomb part. The other two reasons are the overlap effect and the effect stemming from the contributions of CT configuration [17,34], which are taken into account by our method but not by dipole-dipole approximation.…”

“…In Scholes' work [17,19], ethylene dimers are also adopted as example. Here STO-6G is utilized as the basis set.…”

“…The electronic coupling between the initial and final state is a fundamental quantity that measures the speed of EET processes [1,16,17]. The literature on the calculation of the electronic coupling is voluminous [1][2][3][4][5][6][7][8][9][10][16][17][18][19][20][21][22][23][24][25][26].…”

“…There is a lack of reports on investigating triplet-to-triplet (T-T) energy transfer because of complications resulting from exchanging both energy and spin [20]. A general route to calculate the electronic coupling between the donor and acceptor chromophore has been suggested by Scholes' group [17], which involves the effect of a given initial diabatic state electronically couples with more than one final state. The electronic coupling for both the S-S and T-T intermolecular energy transfer is expressed as a concise way.…”

Importance and Nature of Short-Range Excitonic Interactions in Light Harvesting Complexes and Organic Semiconductors

“…[28][29][30] By considering the interaction between Frenkel and charge-transfer excited configurations, 28 they identified the dominant non-Coulombic short range contributions, both depending on intermolecular orbital overlap: a penetration interaction which generally reinforces the Coulombic term, 29 and the Dexter exchange interaction, which opposes it but is of much smaller magnitude. 30 The total excitonic coupling, which captures the global effect of Coulombic and short range contributions, can be computed relatively easily -albeit at a higher computational cost -by using one of the available diabatization techniques based on various molecular properties. 21,[31][32][33][34] In these approaches, the adiabatic electronic Hamiltonian of the system is transformed into a diabatic Hamiltonian where the off-diagonal elements are the couplings between diabatic excited states.…”