A proposal of spin-and charge-modulated open-shell nonlinear optical systems

The second hyperpolarizabilities (γ) for three spin states (doublet, quartet and sextet) of π-conjugated molecules with a charged defect are investigated as a model of novel spin- and charge- modulated nonlinear optical systems. It turns out from the UCCSD(T) results that a charged defect makes the γ̇ negative in sign for low and intermediate spin states (doublet and quartet) while the highest spin, sextet, state exhibits remarkably enhanced positive γ value.