New Organic Nonlinear Optical Polyene Crystals and Their Unusual Phase Transitions

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.

Organic Phenolic Configurationally Locked Polyene Single Crystals for Electro‐optic and Terahertz Wave Applications

“…In order to retain high thermal stability and the tendency for inducing an acentric packing, [9] structurally asymmetric groups were incorporated in the cyclohexene ring of the OH1 chromophore as demonstrated in some previously studied CLP crystals. [9][10][11] The product was purified several times by recrystallization in methanol.…”

“…[7,8] We have recently introduced configurationally locked polyene (CLP) crystals, which are of special interest due to the high tendency for forming acentric crystals with large macroscopic nonlinearity, high thermal stability and the possibility of various melt-and solution-based crystal growth techniques. [9][10][11] The electron donors in these crystals are various dialkylamino or methoxy groups and the electron acceptor is a dicyanomethylidene, >C --C(CN)2 group, in which the CN group can act as a hydrogen bond acceptor site. The main supramolecular interactions of acentric CLP crystals are hydrogen bonds of -CN.…”

“…[9][10][11] The cyano (CN) groups in the electron acceptor form hydrogen bonds with hydrogen bond donor sites in the non-p-conjugated part: for example, H-C groups on the methyl groups in the cyclohexene ring in (2-(3-(2-(4-dimethylaminophenyl)vinyl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (DAT2) [9] and aliphatic H-O group on the prolinol group in 2-(3-(4-(2-(hydroxymethyl)pyrrolidin-1-yl)styryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (PyM3). [11] Here we investigate a novel, very promising CLP crystal, OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile) containing a phenolic electron donor in the p-conjugated part, which also acts as a hydrogen bond donor site. Although the synthesis and the crystal structure of this material have been previously reported, [12,13] its parameters relevant for second-order nonlinear optical applications have not been examined yet.…”

Organic Electro‐optic Single‐ Crystalline Thin Films Grown Directly on Modified Amorphous Substrates

“…A series of acentric configurationally locked polyene (CLP) crystals has been developed recently with large macroscopic nonlinearity and high thermal stability. [10,11] For the growth of thin films on the substrates we choose one of the chromophores 2-{3-[2-(4-dimethylaminophenyl)vinyl]-5,5-dimethylcyclohex-2-enylidene}malononitrile (DAT2, see Fig. 1a) due to a noncentrosymmetric crystal structure (monoclinic P2 1 space group) [12] that leads to large macroscopic nonlinearities.…”

Novel organic material with potential NLO application - electronic and spectroscopic properties

“…Differences between the values for our structure and those for 2-(3-(2-(4-dimethylaminophenyl) v i n y l ) -5 , 5 -d i m e t h y l c y c l o h e x -2 -e n y l i d e n e ) malononitrile (CCDC YEPRIV and YEPQUG [31,32]), 2-(3-(2-(4-dimethylaminonaphthyl)vinyl)-5,5-dimethylcyclohex-2-enylidene)malonitrile (CCDC HEPJIW [33]) and 2-(3-(2-(4-diethylaminophenyl)vinyl)-5,5-dimethylcyclohex-2-enylidene)malonitrile (CCDC HEPJAO [33]) are less then 0.021 Å and 2. (3) o .…”