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Theoretical Study on Nonlinear Optical Properties of Diradical Systems TCNQ and Involving X(X=B,Al, Ga) Atom

Author: LiuHaiBo
Tutor: ChouYongQing
School: Northeast Normal University
Course: Physical and chemical
Keywords: Diradical Character Spin Multiplicity PCM Polarizability Second Hyperpolarizability
CLC: O641.1
Type: Master's thesis
Year: 2011
Downloads: 12
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Abstract


Resently, the studies of organic nonlinear optical （NLO） materials are of major interest because of their special applications, such as large NLO coefficient, short response, high optical damage threshold, molecular design at NLO responsive request, excellent processibility, etc.In recent years, theoretical studies of nonlinear optical properties of organic open-shell systems have paid high attention. Nakano, M et al. deeply studied for nonlinear optical properties of organic open-shell systems. The finding that the spin multiplicity, diradical character y, electron correlation and PCM of pen-shell systems effect on NLO coefficients. Provide the foundations for futher design of radical molecular.We calculate and analyze the third-order NLO properties of the radical systems containing conjugation and X （X=B, Al, Ga） atom. And we discussed the relationship between the conjugation, conjugation length, diradical character, acceptor atom and PCM. The results of our studies in this thesis are:（1） Nonlinear optical coefficients of the closed and open shell systems of TCNQ connecting different conjugation bridgest were computed by using density functional theory （DFT） combining with the finite field （FF） approach. Take the ethylene for an example to discuss the relationship between conjugation length and the NLO properties. The results show that the polarizability and second hyperpolarizability values of open shell systems are larger than those of closed shell systems. Moreover, the polarizabilities and second hyperpolarizabilities become large with the increased conjugation of the conjugation bridge. For the diradical systems, the second hyperpolarizabilities of the singlet increase with the increasing the diradical charactery and spin multiplicity. With the increase of the conjugation bridge length, BLA （Bond Length Alternation, defined as the average of the change of length between adjacent single and double bonds in conjugate molecule.） gradually decrease while the diradical character and second hyperpolarizabilities gradually increase.（2） The polarizability （α） and second hyperpolarizability （γ） have been systemically investigated for singlet diradical complex involving X （X=B, Al, Ga） atom. The results show that bothαandγcan be effectively tuned by varying the distance R （between compound A and a water molecule） and the acceptor atom X. The lone pair electrons from O atom of the water molecule turn into the vacant p orbital of the X atom, which increase the diradical character, leading to the increase of theαandγvalues. Furthermore, the polarizable continuum model （PCM） has been used to test the effects of H2O and CCl4 solvents on theαandγvalues. Bothαandγvalues of the studied diradical complex 1a （1b, 1c） in H2O and CCl4 are uniformly enhanced. And another notable point is that the solvent effects of H2O on bothαandγare larger than that of CCl4.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Structural Chemistry > Chemical bond theory
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