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New Organic Nonlinear Optical Polyene Crystals and Their Unusual Phase Transitions

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  • This work has been supported by the Swiss National Science Foundation.

Abstract

A series of new nonlinear optical chromophores based on configurationally locked polyenes (CLPs) with chiral pyrrolidine donors are synthesized. All CLP derivatives exhibit high thermal stability with decomposition temperatures Td at least >  270 °C. Acentric single crystals of enantiopure D- and L-prolinol-based chromophores with a monoclinic space group P21 exhibit a macroscopic second-order nonlinearity that is twice as large than that of analogous dimethylamino-based crystal. This is attributed to a strong hydrogen-bonded polar polymer-like chain built by these molecules, which is aligned along the polar crystallographic b-axis. Five α-phase CLP crystals with different donors grown from solution exhibit a reversible or irreversible thermally induced structural phase transition to a β-phase. These phase transitions are unusual, changing the crystal symmetry from higher to lower at increasing temperatures, for example, from centrosymmetric to non-centrosymmetric, enhancing their macroscopic second-order nonlinear optical properties.

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