Theoretical studies on photo-triggered second-order nonlinear optical switches in a series of polyoxometalate-spiropyran compounds

The second-order nonlinear optical (NLO) properties of a series of the polyoxometalate (POM)-spiropyran derivatives have been studied by using quantum chemical calculations. The photochemical reaction of spiropyran compounds will produce two different species, spiropyran and merocyanine. The merocyanine species has a large second-order NLO responses because of its good π-conjugated character. And thus a large contrast of the first hyperpolarizability has been obtained. According to quantum chemical calculation, this photo-triggered switchable effect derived from the spiropyran-merocyanine conversion has been enhanced because of introduction of the POM unit. Meanwhile, the substituted effect of the POM species also has been considered in this work. It can be found that introduction of the electron donor/acceptor group into the POM derivative does not significantly affect the magnitude of the first hyperpolarizability.

The second-order nonlinear optical properties of a series of the polyoxometalates-spiropyran derivatives have been calculated by using density functional theory (DFT) combined with the finite field (FF) method.Figure optionsDownload as PowerPoint slideHighlights
► The large contrast on the first hyperpolarizability in spiropyran derivatives.
► The substituted effect of spiropyran derivatives has been discussed.
► The nature of excited state has been described by using TDDFT calculations.
► The effective switching of the first hyperpolarizability across two states.