Structural Design, Growth And Performance Study Of Chalcone System Nonlinear Optical Crystals EBC And BB

Nonlinear optical crystals are key materials for transforming nonlinear optics from theory to practice.Organic nonlinear optical crystals have advantages such as high nonlinear optical coefficient,flexible structural design,and ultra-fast response,and have broad application prospects in fields such as optical communication,optical switches,and second harmonic imaging.This paper presents the design,synthesis,and growth of novel organic nonlinear optical crystals EBC(1-(4-bromophenyl)-3-(4-ethoxyphenyl)-propa-2-en-1-one)and BBC(1-(4-bromophenyl)-3-(4-benzyloxyphenyl)-propa-2-en-1-one)based on the Chalcone system.Experimental characterization and theoretical calculations were conducted to investigate the relationship between structure and performance.The main research contents are as follows:1.Structural design,synthesis,and characterization of EBC crystalsBased on the chalcone structure,bromine was introduced as the electron acceptor,and ethoxy was used as the electron donor.EBC crystal was successfully designed and synthesized,and its single crystal was grown.Powder X-ray diffraction,nuclear magnetic resonance hydrogen spectroscopy,and infrared spectroscopy analysis have confirmed that the synthesized product is EBC.The crystal cell structure of EBC was determined through single crystal X-ray diffraction testing.The first order hyperpolarization,frontier molecular orbital,electronic band structure,total density and partial density of EBC crystal are obtained through quantum chemistry and first principal calculation.The theoretical calculation shows that the introduction of stronger electron donors and electron acceptor into chalcone chromophores can increase the first order hyperpolarization,making chromophores more nonlinear.Ultraviolet visible near-infrared testing shows that the EBC crystal has a transmittance of over 60%in the range of 500-1580 nm,and an optical bandgap of2.75 e V.In addition,EBC crystals exhibit high second harmonic efficiency and high thermal stability.2.Structural design,synthesis,and characterization of BBCBased on EBC crystal,a new electron donor benzyloxy was introduced to form a D-π-A-π-A structure with electron gradient,and a new chalcone crystal BBC was successfully designed and synthesized.Using solution evaporation method to grow a size of 5×5×1 mm~3 of BBC single crystal.BBC crystal belongs to monoclinic crystal system,Pc(7)space group,and has a non-centrosymmetric structure.BBC crystals are direct bandgap compounds with a bandgap of 2.1873 e V.Br atoms and benzyloxy groups are the sources of nonlinear optical properties in BBC crystals.The SHG efficiency of BBC crystal powder is 15 times that of KDP crystal,and the optical band gap is 2.85 e V.At the same time,thermal and dielectric tests were conducted on the BBC crystal powder.Benzyloxy groups with longπ-conjugated structures can exhibit strong electron donating ability,thereby increasing the nonlinear optical properties of crystals.In addition,benzyloxy groups help to form more hydrogen bonds between molecules,thereby improving the thermal stability of the material.Therefore,introducing benzyloxy groups into the chalcone structure is an important strategy for designing nonlinear optical crystals.