Nonlinear optical response in acceptor-substituted carotenoids: a theoretical study

Presented is a theoretical study of the structure and molecular polarizabilities for a set of carotenoid-like molecules. The degree of ground-state polarization is varied by application of an external homogeneous electric field along the long axis of the chromophore. The dipole moment of the apocarotenal molecules evolves stepwise with field, which results in very large values of the first- (α), second- (β), and third-order (γ) molecular polarizabilities. The latter have been evaluated through the sum-over-states expression at the correlated level; simplified three-state and four-term models for β and γ, respectively, have been analyzed in detail. The evolution of the dipole moment μ (and thus the molecular polarizabilities α, α, and γ) can be described adequately as a function of the bond-order alternation structural parameter; the derivative relations among μ, α, α, and γ as a function of bond-order alternation are shown to hold.