دراسة الخواص الضوئية والكهروكيميائية لمركبات بوليمرات اكاسيد الفلزات كمركبات ضوئية لاخطية

A study the Optical and Electrochemical Properties of Polyoxometalate -Based Non-Linear Optical Compounds.

This thesis is divided into three sections: the first includes an introduction to NLO materials and how to generate SHG with an explanation of the connection between the donor and the acceptor and the link between them through π-bridges by the Two-State Model. POM with its types was also discussed, and the most powerful doner that exists, which is julolidine, was also clarified. In the second section, the Schrödinger equation, the four approximations, what quantum chemistry is, and what is HF were explained, after which TDDFT, DFT, and related topics were discussed. In the third section was a discussion of all the results obtained.
Non-linear optical (NLO) materials are used to manipulate laser light through 2nd order phenomena such as second harmonic generation (frequency doubling), and 3rd order effects for instance multi-photon absorption. In this thesis, investigating of NLO materials in which polyoxometalate (POM) electron acceptors is connected via phenylimido groups to organic electron donors is conducted. In this project, we have theoretically, mostly by DFT calculations, systematically studied new compound such as julolidine-based donor groups, very strong donors, as an efficient NLO compound. Their geometric and electronic structures, linear optical and second-order nonlinear properties have also been evaluated. By the introduction of julolidine into the organoimido-hexamolybdate, the studied systems show substantial second-order nonlinear (NLO) responses of up to 1048 × 10−30 esu for compound 3. Upon enlarging the π-conjugated linker, the calculated β-responses are enhanced by a factor of 2.1. Substitution effects (including alkyl and phenyl groups) on donor strength of julolidine and hence on the β -responses have also been investigated. The results showed an enhancement of up to 1.2 in β-responses for phenyl-substituted julolidine derivatives of up to 1242 × 10−30 esu for compound 8.
In general, TD-DFT calculations indicate that the strong low-energy transition can mainly be attributed to charge transfer (CT) from julolidine-arylimido to the hexamolybdate cluster, indicating strong communication between the POM and julolidine components, which is responsible for the linear and non-linear optical behavior of these compounds. Ortho-methylation to the imido-bond has a significant effect on the stability and hence on the length and linearity of the bond, although it slightly reduces the first hyperpolarizability. The whole set of results demonstrates the excellent NLO activity for julolidine-POMs compound while keeping relatively good transparency window compared to similar purely organic systems.