Study On The Synthesis, Nonlinear Optical Activity Of Urea L-malic Acid, A New Organic Nonlinear Material

Nonlinear optical materials are generally applied in high-tech fields such as laser, communication, medical equipment, electronic facility. Studying on chiral organic materials which structure can be changed by purpose is becoming a focus in optical material fields. Now this study is still in the starting phase. Among these studies the Urea, an organic crystal, had been successfully applied in second harmonic generation of ultra-violet. However, because of the easily deliquescence crystal, strict growth condition, and deficient general optical property, the application is narrowed.Urea L-malic acid (ULMA), a new organic nonlinear optical (NLO) crystal, has been synthesized with inputting a chiral molecule-L-malic acid to urea. A series of studies on crystal growth were conducted, the property relation between the chrial and the NLO was primarily studied.During the process of ULMA synthesis and optimize condition, the effects of solution volume, reaction time and temperature were studied, and the optimal condition contained the solution volume as 53mL, reaction temperature as 60℃ and reaction time as 1h. The yield of ULMA was 69.1% in this condition(urea was 0.05mol, L-malic acid was 0.05mol). The effects of revolving rate, reactant proportion, reaction time and temperature on the crystallizing and melting point of ULMA were also analyzed. The morphology and purity of ULMA are good when the reaction time is 2-3 hours and the reaction temperature is 60-70 ℃. The crystal is even when stirring properly and the crystal is easily big with no stirring.The solubilities and supersturation of the crystals in water, methanol, ethanol were been detected in the temperature range of 21.5~46℃, and the formulas of solubility curve have been obtained by curve fitting. Metastable region of urea L-malic acid was got, the relative supersaturation S was comparied. With water substituted by alcohol, the solubilities of ULMA remarkablely decreased and the relative supersaturation 5 substantially increased (methanol had similarly effect, while the result was less than satisfied). It was estimated that methanol solvent orethanol solvent was more benefit to ULMA crystal growth than water, which increased controllable ability of crystal growth.The effects of temperature, growth velocity on ULMA crystal growth were studied primarily. Crystal defects in the crystals and solution stability were discussed. The result was as follows: the key facts of ULMA crystal growth were improving the purity of raw material and solvent, enhancing temperature control, properly selecting supersaturation, stir speed and adopting directional crystal growth technology.From the aspect of the relation between the chiral and the NLO, the effect on optical rotation and nonlinear optical activity of ULMA was explained by inputting L-mailc acid, a chiral molecule. The properties of physical and NLO were detected and analyzed, which indicated that the new organic material was thermal stability, possessed an effective second-order nonlinear optical property and an potential application expectation.