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In the first part of this study, a linear electro-optical (EO) measurement was set up by a simple reflection method. A laser beam aims on the glass substrate at an incident angle q. The incident laser beam is linearly polarized with a 45o polarization angle in respect to the incidence plane so that the parallel (p wave) and perpendicular (s wave) polarized optical fields have equal amplitudes. The beam is transmitted through the ITO-coated substrate, the thin film of NLO material, and then reflected by a gold film. The reflected beam propagates through a Soleil-Babinet compensator, an analyzer and then into a detector. A sinusoidal voltage is applied on the NLO film and the modulation of the laser beam is measured using a lock-in amplifier. Using helium-neon laser (λ = 632.8 nm), an EO coefficient of 30.8 pm/V at the wavelength of the He-Ne laser was obtained for a z-cut LiNbO3 crystal, which is comparable to that reported in literature. The set-up of EO-coefficiency measurement was estabilished and it's operation was confirmed.
For the second part of this study, 5,5'-diamino-2,2'-bipyridine was synthesized for preparing high performance polyimides. The polymers can be coordinated with nickel containing complexes such as (NH3)2Ni(mnt) and Ni(tfd)2, and coordination nickel complex-contained polyimides, PI-Ni(mnt) and PI-Ni(tfd) were obtained.
These metal-coordinated polymeric materials exhibit the improved solubility and mechanical property (high Tg's above 200℃). However, the Td's are lower than those of the pristine polyimides.
A metal-complex coordinated polyimide copolymer coPI50.3, was analyzed by UV-vis and NMR because of its better solubility. An absorption maximum was found at 809 nm. This observation implies the existence of anion of Ni(tfd)- . Moreover, the signals due to the hydrogen atoms of bipyridine ring were not detected by 1H NMR. To further clarity the chemical structure of the metal-complex coordinated polyimide, a series of model compounds were synthesized, and they were analyzed by UV-vis, 1H NMR, and elemental analysis. It was found that a paramagnetic six-coordinated Ni2+ center with two Ni(tfd)- as counter ions presents in the nickel-contained polyimides as well as model compounds. The previously expected second-order NLO active four-coordinated square planar bonding structure was not formed. This study also confirmed that, except the NO2-contained bipyridine complex Ni(5NO2bipy)(tfd), nickel metal complexes are in form of second-order NLO inactive six-coordination in either model compounds or polymer.
To investigate the electro-optical property of the push-pull nickel complex contained in bulk material, a guest-host system based on commercially available polysulfone and Ni(5NO2bipy)(tfd) [doping level = 10 wt%] was prepared. An EO coefficient r33 of 0.7 pm/V was obtained after poling at 165 ℃ (7 kV) for 10 minutes.
在本論文的第一部份，我們成功地架設反射式電光係數(EO coefficient)檢測的儀器。將雷射光的偏振角度固定在與入射面夾45度，使p波(平行入射面)與s波(垂直入射面)的振幅相等，以特定角度θ入射至鍍有ITO透明導電電極的玻璃載體經遇非線性光學材料薄膜，再由鋁製電極層反射，再加一調變電壓(modulation voltage)，以Soleil-Babinet compensator調整p波與s波相對相位至相差π/2，雷射光經一分析片，至光偵器，再以鎖相放大器得到訊號。以氦-氖雷射 (波長=632.8nm)入射至z切割LiNbO3晶體測得其電光係數為30.8 pm/V，與先前文獻上所得之電光係數值相當，証實檢測系統架設成功操作無誤。
製備所得兩系列之含鎳錯合物聚亞醯胺高分子在高溫有好的機械性質(Tg在200 ℃以上) ，但其所預期的熱性質加成性並不如預期，PI-Ni(mnt)系列無明顯增加，而 PI-Ni(tfd)系列增加在10℃左右。含鎳錯合物材料之熱裂解溫度皆不如原本之聚亞醯胺，下降約數十度至一百度左右，其結果與先前4,4’-diamino-2,2’-bipyridine所製備聚亞醯胺及其共聚物之研究有相同的結果。在PI-Ni(tfd)系列中，我們利用合成聚亞醯胺共聚物的方法及選擇溶解度良好之鎳錯合物Ni(tfd)2成功地使形成之材料在常溫下具有良好的溶解度。進一步利用紫外光-可見光(UV-vis)、核磁共振光譜(NMR)、元素分析(EA)等儀器分析其結構。
為了了解含鎳錯合物之非線性光學性質，我們以購得的高分子polysulfone (Tg = 185℃; 溶於THF中)作為高分子基材以Ni(5NO2bipy) (tfd) (10 wt%)製備賓主系統之高分子薄膜，在經165 ℃及7 kV的高電場極化下所得之薄膜量測所得之r33 = 0.7 pm/V，証明含鎳錯合物材料在光電調變材料應用上之可行性。
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