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

我們利用自行架設的克爾光閘超快時間解析螢光(time-resolved fluorescence, TRFL)光譜系統，搭配自行撰寫的一套全自動數據擷取電腦程式來探討電子給體-受體錯合物(electron donor-acceptor, EDA)的分子間電子轉移動力學行為，利用錯合物的光譜資訊以及理論計算來分析，並且提出可能的動力學模型。本論文研究的為非甲基取代苯(non-methyl substituted benzene)-四氰基乙烯(tetracyanoethylene, TCNE)錯合物，包括chlorobenzene (PhCl)-TCNE、fluorobenzene (PhF)-TCNE、benzonitrile (PhCN)-TCNE、p-tolunitrile (p-MePhCN)-TCNE以及p-chlorobenzene (p-ClPhCN)-TCNE錯合物，溶於CH2Cl2以及CCl4溶劑中的電荷轉移(charge-transfer, CT)動力學。　　我們以飛秒雷射脈衝垂直激發非甲基取代苯-TCNE錯合物之電荷轉移吸收譜帶，量測靜態吸收、靜態螢光光譜以及時間解析螢光光譜(time-resolved fluorescence)，來了解錯合物受光激發後從激發態回到基態之動態學過程。我們在這些錯合物中的總螢光衰減函數P(t)擬合了幾個時間常數，我們將最快的時間常數指認為solvation以及激發態之間的內轉換過程，最慢的時間常數指認為激發態經由電荷再結合回到基態的過程。在CH2Cl2溶劑中，PhCl-TCNE、PhF-TCNE、PhCN-TCNE都有著相似的solvation以及IC的時間常數(<0.2)，但有著不同且沒有明顯規律的CR速率(PhCl-TCNE :45 ps、PhF-TCNE :21 ps、PhCN-TCNE:28 ps)。在CCl4溶劑中，PhCl -TCNE、PhF-TCNE、PhCN-TCNE、p-MePhCN-TCNE、p-ClPhCN-TCNE也有著不同的CR速率(PhCl -TCNE: 580 ps, PhF-TCNE: 470 ps, PhCN-TCNE: 140 ps, p-MePhCN: 210 ps, p-ClPhCN: 280 ps)。這些錯合物在極性與非極性溶劑中時間常數的差異，主要來自solvation以及〖∆G〗^0的影響，而我們觀察CR速率與反應自由能變化的關係發現了〖lnk〗_(ET ) V.S.〖-∆G〗^0的曲線有雙反轉(double-inverted region)的現象，我們引用ISM(intersecting state model)理論來分析，可以定性地解釋兩個溶劑中雙反轉的現象。

關鍵字

電子轉移；四氰基乙烯；非甲基取代苯

並列摘要

In this thesis, we used an ultrafast time-resolved fluorescence (TRFL) spectrometer implemented by optical Kerr gating (OKG) and density functional theory calculations to study the electron transfer dynamics in some substituted benzene-tetracyanoethylene (SBZ-TCNE) complexes (SBZ = Chlorobenzene, Fluorobenzene, Benzonitrile, p-Tolunitrile, p-Chlorobenzonitrile) in two solvents (CH2Cl2, CCl4) with different polarities. We used a femtosecond laser to excite the SBZ-TCNE complexes to the charge-transfer (CT) states, and obtained the information from their absorption, fluorescence and TRFL spectra. The analysis of the total fluorescence intensity function P(t), which described the temporal evolution of the population of the excited states and the transition dipole moments, revealed the relaxations of the complexes such as the charge recombination (CR). We found different decay behaviors of the complexes excited states in two solvents. The fastest components of the complexes are in the similar time scale (< 0.2 ps), which is assigned to CT2→CT1 transition, and the slowest one is identified as the CR. The CR time constants of PhCl-TCNE, PhF-TCNE, PhCN-TCNE in the CH2Cl2 are 45, 21, and 28 ps. The CR time constants of PhCl-TCNE, PhF-TCNE, PhCN-TCNE, p-MePhCN-TCNE and p-ClPhCN-TCNE are 580, 470, 140, 210 and 280 ps, respectively. We found that the CR rates of complexes in the polar solvent are faster than in the nonpolar solvent which is mostly due to solvation effects. Surprisingly, the relationship between CR time constants and -∆G0 does not completely obey the Marcus theory and exhibits a double-inversion behavior. We used the intersecting state model (ISM) to explain this unexpected behavior. This model proposed that ultraexothermic reactions accompany large changes in structures which can affect the reorganization energy, and reaction barrier, resulting in the observed double-inversion behavior.

並列關鍵字

electron transfer ； EDA complex

參考文獻

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(22) Chiu, C. C.; Hung, C. C.; Chen, C. L.; Cheng, P. Y.J. Phys. Chem. B 2013, 117 (33), 9734–9756.

(1) Fleming, G. R., Chemical Applications of Ultrafast Spectroscopy Oxford: New York, 1986.

國際替代計量

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

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