Ab Initio Modeling of Donor-Acceptor Interactions and Charge-Transfer Excitations in Molecular Complexes: The Case of Terthiophene-Tetracyanoquinodimethane.

This work presents a thorough quantum chemical study of the terthiophene-tetracyanoquinodimethane complex as a model for π-π donor-acceptor systems. Dispersion-corrected hybrid (B3LYP-D) and double hybrid (B2PLYP-D), hybrid meta (M06-2X and M06-HF), and recently proposed long-range corrected (LC-wPBE, CAM-B3LYP, and wB97X-D) functionals have been chosen to deal with π-π intermolecular interactions and charge-transfer excitations in a balanced way. These properties are exhaustively compared to those computed with high-level ab initio SCS-MP2 and CASPT2 methods. The wB97X-D functional exhibits the best performance. It provides reliable intermolecular distances and interaction energies and predicts a small charge transfer from the donor to the acceptor in the ground state. In addition, wB97X-D is also able to yield an accurate description of the charge-transfer excitations in comparison to benchmark CASPT2 calculations.