Charge-Separation and Charge-Recombination Rate Constants in a Donor–Acceptor Buckybowl-Based Supramolecular Complex: Multistate and Solvent Effects

Abstract

The kinetics of the nonradiative photoinduced processes (charge-separation and charge-recombination) experimented in solution by a supramolecular complex formed by an electron-donating bowlshaped truxene-tetrathiafulvalene (truxTTF) derivative and an electronaccepting fullerene fragment (hemifullerene, C 30 H 12 ) has been theoretically investigated. The truxTTF•C 30 H 12 heterodimer shows a complex decay mechanism after photoexcitation with the participation of several low-lying excited states of different nature (local and chargetransfer excitations) all close in energy. In this scenario, the absolute rate constants for all of the plausible charge-separation (CS) and chargerecombination (CR) channels have been successfully estimated using the Marcus−Levich−Jortner (MLJ) rate expression, electronic structure calculations, and a multistate diabatization method. The outcomes suggest that for a reasonable estimate of the CS and CR rate constants, it is necessary to include the following: (i) optimally tuned long-range (LC) corrected density functionals, to predict a correct energy ordering of the low-lying excited states; (ii) multistate effects, to account for the electronic couplings; and (iii) environmental solvent effects, to provide a proper stabilization of the chargetransfer excited states and accurate external reorganization energies. The predicted rate constants have been incorporated in a simple but insightful kinetic model that allows estimating global CS and CR rate constants in line with the most generalized three-state model used for the CS and CR processes. The values computed for the global CS and CR rates of the donor−acceptor truxTTF• C 30 H 12 supramolecular complex are found to be in good agreement with the experimental values.