Enhancement of nonlinear optical properties in late group 15 tetrasubstituted cubanes

The optical absorption spectra and quadratic hyperpolarisabilities of 1,3,5,7-tetra-substituted cubane derivatives containing group 15 atoms have been investigated computationally using Coulomb-attenuated time-dependent density functional theory. The non-linear optical responses of these octupolar systems are shown to be highly dependent on the group 15 heteroatom with the bismuth-containing derivative displaying large enhancement of its quadratic hyperpolarisability, β, relative to 1,3,5,7-tetraazacubane in vacuo and with acetonitrile solvation. Spin-orbit coupling and scalar relativistic corrections play an important part in determining the value of β for compounds containing As, Sb and Bi.