Intermolecular interaction effects on the second hyperpolarizability of open-shell singlet diphenalenyl radical dimer

Longitudinal static second hyperpolarizability (γ) of open-shell singlet radical dimer is found to be significantly enhanced as compared to that of monomer due to the field-induced intermolecular virtual charge transfer between both-end phenalenyl rings through the strong covalent interaction between the unpaired electrons of the cofacial phenalenyl rings.