A Theoretical And Computational Study On The Photoelectronic Properties Of Organic Optoelectronic Materials

As typical organic optoelectronic materials,the electron donor-? conjugated bridge-acceptor(D-?-A)and similiar structures systems has good prospect in broad applications due to its good photoelectronic properties.These push-pull polyenic systems have simple quasi-one-dimensional structures and can provide theorists good chances testing quantum chemical model.D-?-A structure has many advantages: it has an adjustable donor and acceptor group;P-type or N-type doping can be achieved by the oxidation or reduction of ? electron,respectively,and so on.In order to explore the photoelectronic properties of conjugated systems,quantum chemical methods have been used to study the electronic structures.The electron correlation effect plays a significant role in the study of the optoelectronic properties of the conjugated system.Therefore,the electronic structure method which needs to take into account the electron correlation effect is considered.The level of computer hardware has been developing rapidly in the past decades.Various quantum chemical methods are also improved.Both contribute much in the study of the photoelectronic properties of photoelectronic materials that based on oligomers or polymers.However,with the rapid increase of the system,the computational cost of ab initio quantum chemical method quickly exceeds the computing power of existing computers while the systems studied increases.In recent years,people have turned their attention to the cheaper first principles,the density functional theory(DFT).The DFT method can achieve a reasonable balance between the computational cost and the computational accuracy,and is widely used to study the electronic structure.However,a large number of studies have found that the use of the density functional theory with traditional functional in studying the nonlinear optical properties of the conjugate system is not reliable.Based on finite field scheme,we calculated the longitudinal polarizabilities,first and second hyperpolarizabilities of typical push-pull polyenes by using some electronic structure methods: Hartree-Fock method,M?ller-Plessset perturbation theory,Cluster-Coupled method and density functional theory such as the B3 LYP functional as well as the improvement version CAM-B3 LYP.The extrapolation method is also used to gain electronic correlation effect on the linear and nonlinear polarizabilities,as thechain length grows.The results show that: 1)The traditional DFT method can not correctly describe the nonlinear optical properties of the organic conjugated system.Although CAM-B3 LYP method performs better than B3 LYP,the result is still not satisfactory;2)For the description of linear polarizability,the MP2 method gives wrong results qualitatively,but with the increase of chain length,the trend is improved.For the first and second hyperpolarizability,MP2 gives a qualitatively correct description.However,as the chain length increases,the trend gradually deteriorates;3)CCSD[CCSD(T)] is still the most reliable method to study the nonlinear optical properties of conjugated systems.