| Amino acids participate in life activities as the monomer for protein. Since 1980s, amino-acid derivate crystals as distinctively new-type nonlinear optical (NLO) materials have received more attention.L-arginine phosphate monohydrate (abbreviated as LAP) crystal was firstly discovered by Shandong University as a promising NLO material and has obtained a great deal of authorizations. Japanese scientists indicated that laser-induced damage threshold of LAP crystal is 63 GW/cm2 with wavelength of 1053 nm and pulse-width at 1 ns, furthermore, its deuterated analogue (DLAP) crystal possess extremely high laser damage threshold. The outstanding property attracted worldwide people's attention, and then, many new amino acids derivate crystals with high-quality NLO properties were reported in succession.Arginine is one natural of amino acid, L-arginine trifluoroacetate (LATF) crystal as another NLO crystal material was synthesized by our group for the first time. It belongs to monoclinic crystallographic system with a noncentrosymmteric space group P21. L-arginine cation connected with the trifluoroacetate anion by hydrogen bonds, which form a three-dimensional network in the crystal. The experimental results indicate that the crystal possess good mechanical properties and thermal stabilities, its specific heat is up to 340.70 JK-1mol-1 at room temperature, and more important is that it possess relatively high laser damage threshold. The crystal exhibits an excellent nonlinear characteristic (powder SHG efficiencies is as 2.5 times as that of KDP), the transmission region is from 232 to 2500nm and the degree of transmission is good in the UV-Vis-NIR region.Laser damage mechanism of LAP and LATF crystals is one of the main questions for us. Through sufficient literature investigations, we discover that phosphate arginine (PA) works as themedium carrier for bioenergy transport and storage in invertebrates, as phosphocreatine (PC) in vertebrates. LAP crystal has the same structural units as PA. LATF and PC have the same guanidyl group. The process of stored energy in organism and laser damage in crystals are both correlative to energy, maybe there is some closely association.L-arginine derivate crystals are the object in our dissertation, especially the deuteration studies for discovered LATF crystal, including of crystal growth of DLATF, investigations of crystal properties such as structure, thermal properties, optical properties and laser damage, meanwhile, deuterated studies on another new amino acid derivates have also been carried out. Furthermore, theoretical calculations procedures were exploited to give an insight into the influence on properties of crystals and their deuterated analogues due to the changes of microstructure. The outline of this dissertation is as follows:(1) Bulk crystal growth of DLATFThis is an innovative work carried out in the world for the first time.Through studies on the condition of deuteration for LATF crystal, a method of recrystallized by several times was introduced. The experimental results indicate that the degree of deuteration of DLATF crystals has reached to be 93.4% upwards.The solubility test of LATF crystal was carried out for D2O as solvents by optical schlieren method. The results indicate that it has relatively high solubility and the solubility temperature coefficient and single crystals can be grown from solution by slow cooling. Solution stability and nucleation parameters were investigated, such as metastable zonewidth and induction period were determined and solid-liquid interfacial energy, critical radius and critical energy of nucleus formation were all calculated. In consideration of the growth features of LATF/DLATF crystal, such as large anisotropy, b-axis with largest growth velocity and lamellar growth, a series of measurements were adopted, which includes adjusting the values of pD, keeping the supersaturation of solution and velocity of cooling in an appropriate value. As the result of that, growth morphology of the crystal has been optimized, and several high quality single crystals with the largest size of 48×27×6.3 mm3 were successfully grown.Growth defects and their formation mechanisms were presented. The main defects of DLATF crystals are growth dislocations, inclusions, tapering, cracks, and etching pits namely dislocation out-points were observed by chemical etching method. In the process of crystal growth, concentration of impurity particles, temperature fluctuations and the incongruous supersaturation are all the motivations of bad quality crystals.(2) Investigations of crystal properties of DLATF crystalsThis is another innovative work in the dissertation.X-ray single-crystal diffraction was used to determine the structure of DLATF crystal. It belongs to monoclinic crystallographic system, space group P21, with unit cell parameters:a=10.547(6), b=5.696(3), c=10.825(6) A,?=106.747(10)°,V= 622.8(6) A3 and Z=2, which are smaller than that of LATF crystal. The average lengths of N-D and hydrogen bonds are shortened 0.4% and 0.1% respectively, which indicate that the stability of hydrogen bonds are enhanced after deuteration.IR and Raman spectra show that deuteration makes the vibration frequency of N-H tend to low wavenumber. Harmonic vibration frequency will decline, and the transmission region will tend to infrared region. Furthermore, the disappearing of the bands beyond 3000 cm-1 which are assigned to the stretching of N-H in LATF spectrum reveal that the hydrogen in amino group all have been substituted by deuterium.DLATF crystal possess a higher thermal stability, the melting point is about 222?. The specific heat value is equal to 341.33-536.58 JK-1mol-1 in the temperature range of 293?453 K, which is higher than that of LATF crystal. As one of the most important factors that influence the damage threshold of crystal, so one can guess that DLATF crystal perhaps has a higher damage threshold due to a comparatively lager specific heat. The dielectric constants and the dielectric variation with temperature were recorded, which are anisotropic and independence of the temperature. From the curve of dielectric loss with frequency, we can see that the curve takes an abrupt change with increasing frequency, and tends towards stability at the high frequency.The transmission spectrum of DLATF crystal indicates that it has a transparent region in the 232-2500nm optical region, with an ultraviolet cutoff at 232nm, and the degree of transmission is good in the UV-Visible-NIR region. Compared with that of LATF crystal, the transmission region is broadened distinctly. The refractive indices of crystal were measured by V-prism method, with monochromatic sources generated by Hg, H, He and Na lamps. The dispersion parameter were subsequently fitted using a least-squares fitting program, and the dispersion curves obtained from the fit were plotted. Subsequently, the phase-matching curves were simulated using Matlab program.Many factors have some influence on laser damage, including inherent factors of crystal materials, external factors such as the quality of crystal, component processing, and laser beam. The laser damage threshold of LATF and DLATF crystals were detected under actual laser condition, which are 1.87 and 2.61 GW/cm2 respectively at the laser wavelength of 1053 nm, pulse width of 18 ns. For low repeat frequency strong laser, the laser damage threshold of crystal is correlated with its thermal properties.(3) Two amino-acid derivates have been prepared and grownL-histidine trifluoroacetate (LHTF) crystal and its deuterated analogue (DLHTF) were discovered as two new NLO materials in the course of our study.Studies on the growth conditions for LHTF crystal have been carried out, and the result indicated that the best pH value is about 3.0. Bulk crystals have been successfully grown and its structure has been determined. The crystal belongs to triclinic crystallographic system with a noncentrosymmteric space group P1. The cell parameters are:a=5.1724(6), b=8.8183(12), c=12.481(3) A,?=96.193(17)°,?= 99.853(13)°,?= 102.106(13)°and V=542.26(16) A3,Z=2?A series of characterization have been performed for LHTF and DLHTF crystals. The IR and Raman spectra of DLHTF crystal show that deuteration makes the vibration frequency of N-H tend to low wavenumber. LHTF and DLHTF crystals do not decompose before 200?,which both show high thermal stability and their decomposition curves are consistent with each other. The ultraviolet cutoffs of the two crystals are at 242 nm. After deuteration, the transmission is enhanced distinctively in the 232-2500 nm optical region and the transmission region is broadened to infrared region. Green light emissions were both observed in their powder SHG measurements. The laser damage threshold of LHTF and DLHTF crystals are 1.23 and 1.58 GW/cm2 respectively at the laser wavelength of 1053nm and pulse width of 18 ns.(4) Studies for LATF, LAP molecules and their deuterated analoguesThe conformation of L-arginine molecular will certainly be changed induced by laser irradiation as it exhibits obvious changeability, and the process will consume part energy. However, the conformation variety induced by laser irradiation is quite difficult to be observed directly by experiments. The Raman spectra of LATF and DLATF crystals were studied by Nexus 670 FT-Raman spectrometer in the temperature region of 303-433 K. A series of phenomena such as splitting, broadening and redistribution of intensity were observed with increase of temperature, which makes out that the conformation of molecules will transform due to energy in experiments. Moreover, the difference between responses of LATF and DLATF to temperature indicates that hydrogen bonds in the latter are steadier, which means that more energy will be consumed in the process of laser damage for DLATF crystal.The conformational features of LATF, LAP molecules and their deuterated molecules have been analyzed using Mercury procedure. The optimizations were performed on Gaussian 03 by B3LYP method, and then the molecules spectrums were calculated. The deuterations make the bands at about 3300 cm-1 due to stretching vibration of N-H in?-amino and guanidyl group red-shift to 2500 cm-1. The fact was also observed in experimental spectrum. The first order hyperpolarizabilities of LATF and LAP molecules are 7.397 and 4.265×10-30 esu respectively, which are nearly 27 and 18 times that of urea accordingly, and the values changes due to deuteration.Density of states of LATF, DLATF and LAP, DLAP crystals were calculated using Materials studio by CASTEP procedure. From that we can see, part occupied states changed and band gaps enhanced. In order to study the influence of H and D on density of states of crystals, their local density of state were also calculated, which show a big difference between each other. The molecule and electron of DLATF, DLAP crystal will consume more energy under laser radiation in the process of transition from ground state to excited state. The distribution of charge density represents the basic characteristic of material, and it is different after deuteration, more explorations for the relationship between that and laser damage threshold need to be carried out. |
PDF Full Text Request