Theoretical Study On The Electronic Structure And Nonlinear Optical Properties Of Azulene Nano-chains

Non-linear optics(NLO)materials play an important role in the field of optical information and optical communication.In order to meet the needs of social d e Velopment,researchers are committed to finding NLO active molecules with optimized stability,transparency,and nonlinear optical properties,and designing and synthesizing new NLO materials with superior properties azulene Nano-chain molecules are a special type of structure that are widely used in the fields of physics,optics and chemistry.Different fluorene chains have been synthesized in experiments,and research on fluorene chains is also increasing.The perylene ring itself has polarity,and the charge transfer from the seven-membered ring to the five-membered ring produces a dipole 1.05 Debye from the seven-membered ring to the five-membered ring.Calculations have shown that the azulene also has a certain NLO activity.In this dissertation,ten types of europium nanochains were constructed based on europium rings,and the NLO properties of europium chains were discovered for the first time.In this work,azulene with special optoelectronic properties was used as the research basis,and azulene nano-chain molecules with different connection methods and different lengths were constructed,and a pair of nitroamino groups were selectively introduced to form a D-?-A structure.Using the density functional theory B3LYP method,the 6-31G(d,p)basis set was optimized based on the Gaussian09 program to obtain a stable configuration.The semi-empirical method ZINDO combined state summation method(Sum-Over-States)was used to calculate the electronic spectrum and second-order NLO properties of the system.This thesis consists of two parts.The first part(Chapter 3)designed ten different?-conjugated structures based on the unitary ring.Each structure increases in length along the length of the chain.With the increase of the chain length of different erbium structures,the changes in properties of the stability of the erbium chain structure,the electronic spectrum,the ground state dipole,the static first hyperpolarizability,and the two-dimensional second-order optical spectrum are studied.Analyze the relationship between the electronic structure and the nonlinear optical properties of europium nanochains with different configurations and different lengths.The results show that as the chain length increases,the molecular dipoles increase,but the kinetic stability of each molecule decreases,and the overall absorption peak in the electronic spectrum is red-shifted.The static first hyperpolarizability of different structures also varies with the molecular chain length.The increase showed a marked change.Through analysis and comparison,considering both stability and?₀,molecules with better structure and optimal length were found,and molecular structure characteristics with dynamic stability and excellent nonlinear light response were summarized,which provided further optimization and design of high-quality NLO materials.The second part(Chapter 4)introduces a pair of aminonitro groups into the better structure selected above,studies the second-order nonlinear optical response law by improving the D-?-A structure,and analyzes the structure of the nitroamino pair on the fluorene chain Role.It is interesting to note that the introduction of a nitroamino group in the structure ab-46 at a length of n=4 in structure 10 has an abnormal law for the nonlinear optical effect.The stability and NLO properties of each structure were studied,and detailed discussions and studies were conducted,focusing on the electronic spectrum and NLO properties of the structure ab-46.