Topological Effects on Intramolecular Electron Transfer via Quantum Interference

Abstract

The three isomers of diferrocenylbenzenes (ortho, 1o; meta, 1m; para, 1p) as well as 5-substituted derivatives of m-diferrocenylbenzene with R ) NH 2 (2), Cl (3), CH 3 (4), CN (5), NO 2 (6), and N(CH 3 ) 3 3+ (7) have been prepared. Crystal structures of 1o, 3, and 5 have been solved. In 3 and 5, the cyclopentadienyl rings are nearly parallel to the benzene mean planes with angles ranging from 9.99(5)°to 14.74(5)°. One ferrocene group is above and the other below the mean molecular plane. For 1o, there is an important twist between the benzene and cyclopentadiene rings (68.6(8)°and 32.5(8)°) for steric reasons. Controlled potential electrolysis yields the mixed-valence ferrocene/ ferrocenium species in comproportionation equilibrium with homovalent species. Intervalence transitions have been observed and corrected from comproportionation. From the intervalence band parameters, metal-metal couplings (V ab ) are calculated using Hush's equation. The values are much higher for 1o (0.025 eV) and 1p (0.043 eV) than for 1m (0.012 eV) and exhibit little or no variation for the substituted m-diferrocenylbenzenes 2-6. These results are rationalized by extended Hu ¨ckel molecular orbital calculations. The weakness of the interaction in 1m can be ultimately traced to a quantum Interference effect, i.e., a cancellation of the contributions of two electron transfer paths. This cancellation occurs because each path implies a mixing of metal orbitals with a different ligand orbital, and the resulting molecular orbitals exhibit different symmetries.

Modulation of Internuclear Communication in Multinuclear Ruthenium(II) Polypyridyl Complexes

“…However no evidence of such intervalence features can be identified for 4. The observation that electronic coupling is not as efficient for meta-substituted aromatic rings has already been noted by several groups [33][34][35] . The difference between 4 and 5 in terms of electronic coupling suggesting that the interaction can be explained by a hole transfer superexchange mediated mechanism, since both complexes have similar internuclear separations and hence any through space interactions would be expected to be similar.…”

Spin inelastic currents in molecular ring junctions

“…Interference effects in molecular systems were observed experimentally for electron transfer 36 and molecular junction currents 37 involving derivatives of benzene connected in the meta or para positions. Effects of exciton coherence in photosynthesis were demonstrated in Ref.…”

Cooperative biexciton generation and destructive interference in coupled quantum dots using adiabatic rapid passage

“…This total cancellation of the biexciton generation is due to destructive quantum interference between the different optical pathways available between the ground state and final biexciton state. The signature of such interference has been observed in a broad range of situations, such as the electronic transmission of molecular junctions [53,54] and quantum dots [55], the fission of singlet excited states in molecular crystals [56], or the charge propagation through organic molecules [57,58]. In the CQDs studied here, the four diagonal excitonic states, |X m , act as intermediate states during the excitation of the CQD from its ground state to the biexcitonic state |B 0 .…”