Hetero-π-Dimers of Phenalenyls.

Homogeneous π-stacking dimers of phenalenyl and its derivatives have gained tremendous interest as components of conducting organic materials. For the first time, we investigate theoretically heterogeneous phenalenyl π-dimers. Key parameters, including charge transfer, interaction energy, singly occupied molecular orbital (SOMO) energy, and spin density, are studied with the help of density functional theory. We find that the amount of charge transfer between the two monomers in phenalenyl π-dimers correlates with the difference in the SOMO energies of the constituent monomers, where the SOMO energy plays the role of a monomer (group) electronegativity index. Charge transfer plays an important role in stabilizing the heterodimers while maintaining a significant diradicaloid character. For five heterodimers the interaction energy is found to be as large as -30 to -50 kcal mol(-1) . The presented correlation between the monomer SOMO energy levels and their stability can provide a simple predictive tool to design new highly stable π-stacking heterodimers.