Intramolecular Polarization Induces Electron–Hole Charge Separation in Light-Harvesting Molecular Triads

Abstract

Artificial light-harvesting supramolecular structures reproduce the light-to-electrochemical energy transduction mechanisms observed in natural photosynthesis. Among them the prototypical carotenoid­(C)–porphyrin­(P)–fullerene­(C₆₀) type of structures have been the most studied. Several experiments performed in such structures, and others alike, have shown that the photoexcited state <i>C</i>– ¹<i>P</i>–<i>C</i>₆₀ decays to the metastable charge-separated state <i>C</i>– <i>P</i>^•+ −<i>C</i>₆₀^•– within a few picoseconds, whereas the final charge-separated state, <i>C</i>^•+– <i>P</i> −<i>C</i>₆₀^•–, is obtained within hundreds of picoseconds. This paper introduces a nonlinear polarizable extended Hückel Hamiltonian that describes the charge dynamics and charge-separation effects in such triads by means of quantum dynamics simulations performed on the photoexcited electron–hole pair. The results are interpreted on the basis of the discrete self-trapping equation and enlighten the role played by the polarizability on charge-separation phenomena