Density Functional Theory Study on Subtriazaporphyrin Derivatives: Dipolar/Octupolar Contribution to the Second-Order Nonlinear Optical Activity

Density functional theory calculations have been carried
out on
the subtriazaporphyrin skeletons, an excellent prototype for investigating
the dipolar/octupolar contribution to the second-order nonlinear optical
(second-order NLO) activity, revealing the size effect and clarifying
the nature of the limit when expanding the conjugated system is employed
to improve the hyper-Rayleigh scattering response coefficient (βHRS). The octupolar and dipolar contributions are theoretically
separated, rendering it possible to control the dipolar/octupolar
second-order NLO contribution ratio by changing the number and orientation
of the peripheral fused benzene moieties. In addition, both the dispersion
and solvent effect were also revealed to lead to the enhancement of
βHRS.