Cooperative effects in static polarizabilities and second hyperpolarizabilities of hydrogen-bonded 4-pyridones

Second hyperpolarizabilities (γ) of hydrogen (H)-bonded 4-pyridones (θ = 0°) exhibit a significant increase of γ per monomer for the increase of the number of monomers due to the strong cooperative effects on γ originating in the covalent interaction between π-systems through H-bonds in the virtual excitation processes.