行政院國家科學委員會專題研究計畫 成果報告
光學高分子溶液的瞬時線性和非線性光散射研究
計畫類別： 個別型計畫 計畫編號： NSC92-2112-M-110-022- 執行期間： 92 年 08 月 01 日至 94 年 01 月 31 日 執行單位： 國立中山大學物理學系(所) 計畫主持人： 王進賢 計畫參與人員： 陳國瑋,戴永輝 報告類型： 精簡報告 報告附件： 出席國際會議研究心得報告及發表論文 處理方式： 本計畫可公開查詢中 華 民 國 94 年 3 月 23 日
91/10/30 修訂
行政院國家科學委員會專題研究計畫 成果報告
光學高分子溶液的瞬時線性和非線性光散射研究
計畫類別： 個別型計畫 計畫編號： NSC 92－2112－M－110－022 執行期間： 92 年 08 月 01 日 至 94 年 01 月 31 日 執行單位： 國立中山大學物理學系(所) 計畫主持人： 王進賢 計畫參與人： 陳國瑋,戴永輝 報告類型： 精簡報告 報告附件： 研究心得報告及發表論文 處理方式： 本計畫可公開查詢中 華 民 國 94 年 3 月 23 日
91/10/30 修訂 二
、
A.中文摘要：
由於共軛高分子 (conjugated polymer)及非線性光學分子在可見光範圍吸收很強，因 此靜、動態光散射量測研究還未被開發。本計畫用紅外光雷射為激發光源進行非線性光 學分子及共軛高分子溶液的光散射實驗。儘管在紅外光散射效率低，偵測器靈敏度也 低，紅外光散射實驗卻可以得到共軛高分子及非線性光學分子在溶液中的鏈型態 (conformation) 及熱力學的相關資訊。由於接近退休年齡，本計畫完成可行性的實驗。非 線 性 光 學 發 色 團 (chromophores) 的 第 一 分 子 超 極 化 率 (first molecular hyperpolarizability)，β，可以經由超瑞利散射 (Hyper-Rayleigh scattering, HRS) 的實驗 得到。目前大部分的 HRS 實驗都是以波長 1064 nm 的雷射光為激發光源。以這波長為 激發光源所測量到的β值不準確。用長波長的紅外雷射光來激發 HRS 可減少因雙光子 吸收 (two-photon absorption) 引發的螢光及雙光子共振增強 (two photon resonance enhancements)的干擾。以長波長雷射光激發的 HRS 實驗很重要，因為它可提供精確的 本質第一超極化率，進一步精準地得到非線性光學發色團和分子結構與特性的關係。本 年以可調的雷射波長做 HRS 實驗，研究第一分子超極化率與波長的關係及色散效應。 在測試 HRS 時，發現某些共軛非線性光學分子散發雙光子螢光。為了解其性質，本年 也深入探討雙光子螢光的現象，發明測量雙光子吸收截面積的新方法。 關鍵詞：共軛高分子，共軛高分子溶液，高分子型態和鏈與鏈之間交互作用，非線性光 學發色團，非線性光學高分子溶液，紅外光激發靜態及動態光散射，頻率有關的超瑞利 散射，第一分子超極化率的色散，雙光子吸收截面積。 B. 英文摘要
Studies of optical and thermodynamic properties of photonic molecules in solution using spontaneous linear and nonlinear laser light scattering techniques have been carried out. Static and dynamic light scattering, widely used for the characterization of the property of polymer solution, has not been exploited in conjugated polymer solutions, due to strong absorption of the laser light in the visible spectral region. Infrared radiation was used as the excitation source to carry out the light scattering experiment on the conjugated polymer solutions. Despite weak scattering efficiency and low detector sensitivity, the infrared light scattering experiment yields a wealth of information about polymer chain conformation and the thermodynamic property of conjugated polymers in solution; however, due to the approach of compulsory retirement age, only feasibility studies were made in the infrared dynamic light scattering experiment.
Hyper-Rayleigh scattering (HRS) employing different laser excitation wavelengths were used to investigate the frequency dependence of the first molecular hyperpolarizability of nonlinear optical (NLO) chromophores and NLO polymers. Most HRS measurements carried out elsewhere employ the 1064 nm excitation wavelength. Recent HRS work in this laboratory has extended the experiment to longer excitation wavelengths, such as 1543 nm and 1907. At long wavelength, interference due to two-photon absorption induced fluorescence is removed; one and two photon resonance enhancements are also reduced to a minimum. The long wavelength HRS experiment is important, as it will provide one with accurate intrinsic first hyperpolarizability data, thus enabling one to critically evaluate the structure/property relationship of the NLO chromophores and polymers. Measurements of the wavelength dependence of the first molecular hyperpolarizability were carried out and the effect of the dispersion on the nonlinear optical nonlinearity of NLO polymer was elucidated. During the course of the HRS, two photon absorption induced fluorescence was
91/10/30 修訂
observed. Studies of the two photon fluorescence led to the invention of a new technique for measuring two-photon absorption cross sections of NLO chromophores.
Keywords：Nonlinear optical chromophores; nonlinear optical polymers solutions; static and dynamic light scattering using infrared excitation; frequency dependent hyper-Rayleigh scattering; dispersion of first molecular hyperpolarizability; two-photon absorption cross sections.
三
、
內容及成果Recent research has demonstrated charge-transfer molecules with an electron-donor group and an electron-acceptor group attached to both ends of a core consisting of conjugated π-electron moiety exhibit large second-order nonlinear optical (NLO) effects, such as second harmonic generation, linear electro-optical (LEO) and photorefractive effects. The push /pull mechanism endows the molecule with a large dipole moment. When these molecules are incorporated in the glass-forming polymer on the main chain or as the side chain to form a NLO polymer, they have potential applications in high-speed optical switches. Characterizations of such chromophores and polymers in solution have fundamental and technological importance. Research carried out this year consists of: 1) static and dynamic light scattering studies of conjugated polymers in solution to investigate the process of aggregate formation; 2) an in-depth study of the dispersion of the first molecular hyperpolarizabilities of NLO polymers using different excitation laser wavelengths. The publications listed below summarize the projects that have been completed:
1. “Hyper-Rayleigh scattering and frequency dependence of the first molecular
hyperpolarizability of a strong charge-transfer chromophore”, C. H. Wang, Y. C. Lin, Oliver Y. Tai, and Alex K.-Y. Jen, J. Chem. Phys. 119, 6237 (2003).
2. “Wavelength dependence of first molecular hyperpolarizability of a dendrimer in solution”, Oliver Y.-H. Tai, C. H. Wang, H. Ma, and Alex K.-Y. Jen , J. Chem. Phys. 121, 6086 (2004).
3. “One-, two-, and three-photon absorption induced fluorescence of a novel chromophore in chloroform solution”, Yuxiao Wang, Oliver Y.-H. Tai, C. H. Wang, and Alex K.-Y.Jen, J. Chem. Phys. 121, 7901 (2004).
4. “Non-quadratic-intensity dependence of two-photon absorption induced fluorescence of organic chromophores in solution”, C. H. Wang, Oliver Y.-H. Tai, Yuxiao Wang, Tsung-Hsiu Tsai, and Nein-Chen Chang, J. Chem. Phys. 122, 084509 (2005).
Two students have completed their graduate studies dealing with the present research: 1. 陳國瑋之碩士論文:交互擴散於 P4VP/CHCl3 溶液之準彈性光散射量測 (Mutual Diffusion of poly(4-vinylpyridine) inchloroform probed by quasielastic light scattering),物 理學系研究所,92 學年度
2. 戴永輝之博士論文:以非線性光學散射與吸收研究強電荷轉移分子 (Investigations of strongly charge transfer molecules using nonlinear optical scattering and absorption) ,物 理學系研究所,93 學年度
