透過您的圖書館登入
IP:34.234.83.135
  • 學位論文

以超快時間解析光學克爾光閘螢光光譜研究苯取代基-四氰基乙烯錯合物分子間電荷轉移動態學

Ultrafast Time-Resolved Optical Kerr Gating Fluorescence Studies of Intermolecular Charge Transfer in Substituted-Benzene-Tetracyanoethylene Complexes

指導教授 : 鄭博元
若您是本文的作者,可授權文章由華藝線上圖書館中協助推廣。

摘要


本論文利用自行架設之克爾光閘時間解析螢光光譜儀(optical kerr gating time-resolved fluorescence spectroscopy)探討甲基取代苯(p-XY,TOL,BZ)與四氰基乙烯(TCNE)在CCl4和CH2Cl2溶劑中形成的電子給體-受體錯合物,以飛秒雷射脈衝激發甲基取代苯-四氰基乙烯錯合物的電荷轉移吸收譜帶(charge transfer band),再搭配時間解析螢光光譜 (time-resolved fluorescence, TRFL)與理論計算結果探討三種錯合物從激發態回到基態的動態學過程。我們提出一個總發光強度函數P(t)用來描述激發態分子在鬆弛(relaxation)過程中,激發態佈居數(population)與躍遷偶極矩(transition dipole moment)隨時間的變化,我們可以觀察到三種錯合物在CH2Cl2和CCl4溶劑中都存在一個非常快的衰減成分(< 0.2 ps),我們將此過程指認為CT2→CT1的IC。在極性溶劑CH2Cl2中,p-XY-TCNE( 、415 nm)、TOL-TCNE( nm)和BZ-TCNE( nm)的電荷再結合時間常數分別為0.6 ps、0.5 ps、7 ps及29 ps。在非極性溶劑CCl4中,p-XY-TCNE( 、415 nm)、TOL-TCNE( nm)和BZ-TCNE( nm)的電荷再結合時間常數分別為280 ps、280 ps、850 ps及150 ps。 我們觀察到甲基取代苯-四氰基乙烯在CH2Cl2溶劑中的電荷再結合速率非常符合Marcus反轉區域(inverted region),即驅動力(driving force, )愈大會使得電子轉移速率愈慢;然而在CCl4溶劑中, BZ-TCNE錯合物卻明顯偏離Marcus反轉區域,我們利用交叉態模型(intersecting state model, ISM)解釋其偏差,即必須考慮錯合物結構改變的影響,ISM提出Marcus理論中兩條位能曲面不只會垂直移動也會水平移動,使得反應能障 發生變化進而影響電子轉移速率。最後,我們比較在不同極性溶劑中對錯合物電荷再結合速率的影響,可以觀察到極性溶劑中的電荷再結合速率明顯較快,這是因為強大的polar solvation效應所造成。值得注意的是,p-XY-TCNE和TOL-TCNE錯合物在CH2Cl2溶劑中的電荷再結合皆應發生在未平衡狀態,即尚未完全solvation或振動鬆弛就回到基態。

關鍵字

動力學 錯合物 超快 飛秒

並列摘要


We employed a broadband ultrafast time-resolved fluorescence (TRFL) spectrometer implemented by the optical Kerr gating (OKG) to study the charge transfer (CT) state dynamics of methyl-substituted benzene-tetracyanoethylene (MBZ-TCNE, MBZ = benzene, toluene and p-xylene) in two solvents (CH2Cl2, CCl4) of diffrernt polarities. The CT-state of the MBZ-TCNE complexes are reached via femtosecond laser excitation, and the observed TRFL spectra reveal CT-state relaxation dynamics from the initial CT-state to charge recombination (CR). We used a total fluorescence intensity function P(t) to describe the excited-state population and transition dipole moment evolution with time during CT-state relaxation. The three complexes studied in two solvents exhibit a very fast initial decay component of similar time scale (< 0.2 ps), which can be assigned to CT2→CT1 internal conversion. The CR time constants for p-XY-TCNE (λex = 383 nm), TOL-TCNE ( nm) and BZ-TCNE ( nm) are 0.6, 7 and 29 ps in CH2Cl2. The equilibrium CR time constants for p-XY-TCNE (λex = 383 nm), TOL-TCNE ( nm) and BZ-TCNE ( nm) are 280, 850 and 150 ps in CCl4. The CR rate constants of MBZ-TCNE in CH2Cl2 are in line with the expectation for the Marcus inverted region, but CR rates in CCl4 do not agree with Marcus inverted region. The unexpected reversed -G0 dependence of the equibrium CR rates in CCl4 can be explained by the intersecting state model (ISM), which takes structural relaxation of complexes into account. Finally, CR rates of the CT-state of these MBZ-TCNE complexes are much faster in polar solvents due to the strong polar solvation.

並列關鍵字

dynamics complex ultrafast femtosecond

參考文獻


58. 邱志忠, 清華大學化學系博士論文 2013.
72. Umapathy, S.; Lakshmanna, A.; Mallick, B., J. Raman Spectrosc. 2009, 40 (3), 235-237.
5. Liu, M.; Ito, N.; Maroncelli, M.; Waldeck, D. H.; Oliver, A. M.; Paddon-Row, M.
50. Kinoshita, S.; Ozawa, H.; Kanematsu, Y.; Tanaka, I.; Sugimoto, N.; Fujiwara, S., Rev. Sci. Instrum. 2000, 71 (9), 3317-3322.
55. Schmidt, B.; Laimgruber, S.; Zinth, W.; Gilch, P., Appl. Phys. B Lasers Optic 2003, 76 (8), 809-814.

延伸閱讀