Structural reorganizations control intermolecular conductance and charge trapping in paraquat-tetraphenylborate inverse photochemical cell.

Miniaturization of electronic devices to the level of single molecules requires detailed understanding of the mechanisms of their operation. One of the questions here is the identification of the role of structural alterations in charge separation and stabilization in photoactive complexes. To address this question, we calculate optimized molecular and electronic structures, and optical and vibrational spectra of l,l'-dimethyl 4,4'-bipyridinium-bis tetraphenylborate PQ(BPh4)(2) complex ab initio using density functional theory approach and compare them with the experimentally observed UV-Vis and Raman spectra of the molecules in solid-state films. The results indicate that the association of PQ and BPh4 leads to the formation of an internally ionized structure that is accompanied by the structural reorganization of both PQ (the twisting of pyridinium rings) and BPh4 (phenyl rings rotation) moieties. The quanta of light do not seem to be directly involved in the formation of this ionized structure, but provide energy for fast recombination of the separated charges between BPh4- and PQ(2+). The high efficiency of the dark charge separation and the stabilization of separated charges in the complex permit the using of PQ(BPh4)(2) in various charge-transfer devices like molecular probes, photovoltaic devices or chemical memory units.