Optical Characterization Of Newly Synthesized Chiral Compounds

Our investigation explores the relationship between molecular structure and optical properties of compounds. Non-linear optical features are observed in molecules that lack a center of symmetry. These features have several applications in telecommunication, optical storage and all-optical signal-processing. The understanding of how structure correlates to optical activity is essential to be able to optimize non-linear optical effects. The focus of this project is a series of compounds that vary slightly in structure. These are either thiocarbamates prepared by reacting aryl iso-thiocyanates (ITC) with an enantiopure chiral alcohol such as 2(S)-butanol or they are thioureas which result upon the reaction of the ITC with (S)-α-methylbenzylamine (MBA). Basic organic synthesis skills such as column chromatography, thin layer chromatography (TLC) and nuclear magnetic resonance (NMR) were utilized to isolate the desired compounds. Recrystallization was conducted to obtain crystals required for X-ray diffractometry. The structures obtained with X-rays served as input data for numerical model calculations. These models gave detailed tensorial information on refractive indices, optical rotation, electro-optic coefficients and second harmonic generation (SHG) efficiency. The software was specifically developed to be applicable to crystals. To compare the calculated properties to experimentally determined values, the Kurtz test was performed. Here, the intensity of light of twice the frequency than that of the initial laser light is measured in powders which provide SHG signatures of the new compounds to be compared with those calculated. The goal is to observe how the optical properties vary from compound to compound, which differ slightly in molecular structure.