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  • 學位論文

超快時間解析螢光光譜研究四氰基乙烯-甲基苯錯合物之分子間電荷轉移動力學

Ultrafast Time-Resolved Fluorescence Studies of Intermolecular Charge Transfer Dynamics in Tetracyanoethylene-Methylbenzene Complexes

指導教授 : 鄭博元
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摘要


我們利用實驗室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)的分子間電子轉移行為,利用錯合物的光譜資訊並搭配理論計算(Gaussian 09)的分析,並提出了可能的動力學模型。本論文研究的是四氰基乙烯-甲基苯取代錯合物(Tetracyanoethylene-Methylbenzene)溶於CH2Cl2及CCl4的電荷轉移(charge-transfer , CT)動力學,我們量測了TCNE-p-Xylene錯合物的光譜學行為,並配合實驗室前人對TCNE-Benzene、TCNE-Toluene的研究,綜合討論取代基對靜態、動態光譜的影響。另外,TCNE-p-Xylene擁有兩種構型,我們藉由調變激發波長來改變對不同構型的激發比例,一併分析了不同構型對光譜學的變化。我們測量靜態吸收光譜得到三種錯合物CT譜帶的位置,進而選定適當的激發波長激發錯合物的CT譜帶,並觀察錯合物在激發態中的TRFL光譜隨時間的變化。最後我們以總螢光強度(p(t))及平均放光頻率( (t))來分析錯合物在液相中,激發態的電荷再結合動態學。概括來講,錯合物經由初始激發至激發態後,伴隨快速的分子內轉換及結構緩解、震動緩解至較低能量的穩定態,接著發生電荷再結合完成一系列的電荷轉移動力學。動力學的擬合結果顯示,三種錯合物有著差不多的IC常數(< 0.2 ps),但有著較為不同的CR速率(CH2Cl2: TCNE-Benzene 29 ps,TCNE-Tolulene 7 ps, TCNE-p-Xylene 0.5 ps ; CCl4 : TCNE-Benzene 150 ps,TCNE-Toluene 820 ps, TCNE-p-Xylene 290 ps )。另外三種錯合物在極性、非極性溶劑中的時間常數有著顯著落差,針對這兩種現象,我們大致利用電子給體的游離能及solvaiton來討論時間常數的差異,並考量電子偶合強度造成的影響。值得一提的是,本論文引進ISM(intersecting state model)的解釋,概略的分析了一系列TCNE-甲基苯取代錯合物在CCl4中,CR時間常數隨自由能的雙反轉趨。

並列摘要


This dissertation employed an ultrafast time-resolved fluorescence (TRFL) spectrometer implemented by optical Kerr gating (OKG) and density functional theory calculations implemented in the Gaussian 09 program to study electron transfer dynamics in tetracyanoethylene-methylbenzene (TCNE-MBZ) complexes (MBZ = Benzene, Toluene, p-Xylene) in two solvents (CH2Cl2, CCl4) of different polarities. We used femtosecond laser to excite the TCNE-MBZ complexes to the CT-states, and the resulting TRFL spectra were measured. Analyses of the total fluorescence intensity function P(t), which describes the temporal evolution of excited state population and transition dipole moment, revealed complex relaxations associated with charge recombination (CR). We found different decay behaviors in two solvents. The fastest component which are in the similar time scale (< 0.2 ps) for the three complexes is assigned to CT2→CT1 transition, and the slowest component is ascribed to CR. The CR time constants in CH2Cl2 for TCNE-p-Xylene, TCNE-Toluene, TCNE- Benzene are 0.5, 7 and 29 ps, respectively, The CR time constants in CCl4 for TCNE-p-Xylene, TCNE-Toluene, TCNE- Benzene are 290, 820 and 150 ps, respectively. We concluded that CR time constants are consisted with the behavior in the Marcus inverted region. However the CR rates in CCl4 is reverted when the driving force(-∆G0) increase in the case of TCNE-Benzene. We use the intersecting state model (ISM) to explain this unexpected behavior. ISM accounts for structural relaxation of complex which the Marcus theory does not consider. Finally, we found that the CR rates of complexes in polar solvent is faster than in nonpolar solvent, which is mostly due to solvation effet.

並列關鍵字

Ultrafast Dynamics kinetics

參考文獻


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被引用紀錄


陳冠劭(2017)。以超快時間解析螢光光譜研究非甲基取代苯-四氰基乙烯錯合物之分子間電子轉移動力學〔碩士論文,國立清華大學〕。華藝線上圖書館。https://www.airitilibrary.com/Article/Detail?DocID=U0016-0401201816095217

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