Study On The Structure Optimization And Nonlinear Properties Of Two-Dimensional Spindle-Type Chromophores

Second order nonlinear optical(NLO) materials have drawn great attention owing to their application in many fields such as optic information storage and processing, optical sensing, telecommunications etc. Organic NLO materials which have many advantages such as ultrafast response, wide response wave band, ease of processing and low cost have been widely investigated so far. Organic chromophores are the key constructing block for organic NLO materials. Designing and synthesizing high hyperpolarizability chromophores with high poling efficiency and good thermal stability as well as chemical stability is of great significance for the NLO materials.In this dissertation, we provide some promising attempts to investigate the poling efficiency and hyperpolarizability basing on the synthesis of two-dimensional spindle-type chromophores. We design and synthesize a series of alkyl functioned two-dimensional spindle-type chromophores via introducing alkyl group to the phenyl isolators. We also study the influence of alkyl structures on the poling efficiency. Besides, we design and synthesize the chromophores with the novel D-D’-π-A’-A and D-A’-π-D’-A structures. Basing on these chromophores, we study the relationship between the structure and microscopic NLO property at the molecular level.In chapter 2, we design and synthesize a series of alkyl functioned two-dimensional spindle-type chromophores. We introduce the 4-hydroxymethylphenyl to the phenyl conjugated bridge and form the two-dimensional spindle-type chromophores firstly. And then we introduce the alkyl groups with different structures to the phenyl group of the two-dimensional spindle-type chromophores which can further block the intermolecular interaction and a series of alkyl functioned two-dimensional spindle-type chromophores are prepared for poling efficiency investigation. The alkyl groups include t-butyl group, n-butyl group and n-octyl group. The electro-optic coefficients and poling efficiency of the chromophores show improvement by introduction of alkyl in various degree, and n-octyl functioned chromophores show the best poling efficiency and electro-optic coefficients. The UV–vis absorption of chromophores in different solvents varying dielectric constants are measured and the results demonstrate that all the chromophores have the similar absorption which may account for the methane which block the alkyl to participate in the resonance structure of chromophores and influence the hyperpolarizability. DSC results show that n-butyl and n-octyl functioned chromophores display melting points before decomposition, this may be due to the weaken intermolecular action caused by the introduction of n-butyl and n-octyl. Thermal properties of the chromophores are characterized by TGA, all chromophores display good thermal stability, Td is above 200 ℃, except the t-butyl functioned chromophore have a little decrease.In chapter 3, we design and synthesis the chromophores containing both auxiliary donors and auxiliary acceptors on their conjugated bridge termed D-D’-π-A’-A and D-A’-π-D’-A structures for structure and microscopic NLO property relationship investigation. The auxiliary donors and acceptors of D-D’-π-A’-A structure chromophores are introduced close to the donors and acceptors respectively and D-A’-π-D’-A structure chromophores had the opposite distribution of the auxiliary donors and acceptors. The chromophores structures are characterized by the 1H-NMR and FT-IR spectrum. D-D’-π-A’-A structure chromophores show a different chemical shift and a redshifted maximum UV absorption wavelength compared to D-A’-π-D’-A structure chromophores which may be both related to the alterative intramolecular charge transfer and hyperpolarizability, and the redshifted maximum UV absorption wavelength can be a reflection of improved hyperpolarizability. The theoretical calculation results are consistent with the experimental results, D-D’-π-A’-A structure chromophores have the higher dipole moment and hyperpolarizability compared to D-A’-π-D’-A structure chromophores. TGA and DSC characterizations of the chromophores show that all the chromophores have the similar good thermal stability and Td is all above 200 ℃.