以超快時間解析光學克爾光閘螢光光譜研究烯烴類-四氫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 Olefin-Tetracyanoethylene Complexes

顏煒城(Wei-Cheng Yen)

指導教授 ： 鄭博元

國立清華大學/理學院/化學系所/碩士(2018年)

摘要

本論文利用實驗室自行架設的光學克爾光閘超快時間解析螢光(time-resolved fluorescence, TRFL)光譜系統，及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(electron donor-acceptor, EDA)錯合物的分子間電子轉移動力學行為，結合錯合物的光譜資訊以及理論計算，提出可能的動力學模型。本論文研究的為烯烴類(olefin)-四氰基乙烯(tetracyanoethylene, TCNE)錯合物，包括1-hexene-TCNE、2-hexene-TCNE、1-methylcyclohexene-TCNE以及2,3-dimethyl-2-butene-TCNE錯合物，溶於極性-CH2Cl2以及非極性-CCl4溶劑中的電荷轉移(charge-transfer, CT)態動力學。我們藉由靜態吸收光譜的結果選擇適當的波長以飛秒雷射脈衝垂直激發錯合物之電荷轉移吸收譜帶，量測靜態螢光光譜、時間解析螢光光譜以及瞬態吸收光譜，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。在TRFL光譜中我們藉由分析總體螢光強度隨時間的變化(P(t))獲得的時間常數，並且利用瞬態吸收光譜所得到的結果，來幫助我們指認時間常數。在極性溶劑CH2Cl2中可以獲得2個指數衰減常數，一個為超快的衰減常數(<0.3 ps)，另一個為約在1-3 ps尺度的衰減常數；而在非極性溶劑CCl4中一樣是獲得2個指數衰減常數，一個為超快的衰減常數(<1 ps)，另一個為約在十幾皮秒尺度的衰減常數。我們將較快的衰減常數指認為激發態錯合物的結構鬆弛所造成的衰減，而較慢的衰減常數則指認為因為回覆電子轉移反應而造成CT態的佈居數衰減。接著，我們結合實驗室前人研究的一系列甲基與非甲基取代苯(arene)-四氰基乙烯錯合物之結果，與本論文所研究的olefin-TCNE錯合物之結果相互比較，觀察到當電子給體由arene改變成olefin時，在相近的反應自由能下，olefin-TCNE錯合物之回覆電子轉移速率是比較快的。而在回覆電子轉移速率與反應自由能的關係中發現olefin-TCNE錯合物系統隨著-∆G0的增加，回覆電子轉移速率的變化較arene-TCNE錯合物系統平緩，即olefin-TCNE錯合物系統相較於arene-TCNE錯合物系統對於-∆G0的依賴性並不大。

關鍵字

電荷轉移 ； 電子給體-受體錯合物 ； 四氫基乙烯

並列摘要

The charge-transfer (CT) state relaxation dynamics of a series of electron donor-acceptor (EDA) complexes was studied with broadband ultrafast time-resolved fluorescence spectroscopy implemented by optical Kerr gating. The EDA complexes studied here are those containing various arenes or olefins as the donor and tetracyanoethylene (TCNE) as the acceptor. In our experiments, the CT state of the EDA complexes are directly reached by femtosecond laser excitation in either CH2Cl2 or CCl4 solutions, and the subsequent temporal evolution of the fluorescence spectra were measured to explore the charge recombination (CR) dynamics. EDA complexes with various arenes, including methyl substituted and non-methyl substituted benzenes, as the donor have been studied previously in our laboratory. Here, we present our data on CT state relaxation and CR dynamics of EDA complexes containing a series of olefins (1-hexene, 2-hexene, 1-methylcyclohexene, 2,3-dimethyl-2-butene) as the donor and TCNE as the acceptor. 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. We found two CT-state decay behaviors of the complexes in these two solvents. The faster components of the complexes are in the similar time scale (<0.3 ps in CH2Cl2；<1 ps in CCl4), which are assigned to the structural relaxation of the CT state, and the slower ones (1-3 ps in CH2Cl2；10-20 ps in CCl4) are identified as the CR. We found that the CR rates of olefin-TCNE complexes are faster than arene-TCNE complexes with similar driving force (-∆G0) for electron transfer. Surprisingly, the CR rate constants are strikingly nonvariant among the different olefin-TCNE complexes despite large differences in the driving force (-∆G0) for electron transfer.

並列關鍵字

Charge transfer ； EDA complex ； Tetracyanoethylene

參考文獻

Chapter 1 Reference

1. Barbara, P. F.; Meyer, T. J.; Ratner, M. A., J. Phys. Chem. 1996, 100 (31), 13148-13168.

2. Kuznetzov, A. M.; Ulstrup, J., Electron Transfer in Chemisry and Biology：an introduction to the theory. Wiley series in Theoretical Chemistry, 1999.

3. Taube, H., Electron Transfer Reactions in Solution. Academic：New York, 1970.

4. Sit, P. H. L.; Cococcioni, M.; Marzari. N., Phys. Rev. Lett. 2006, 97 (2).