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

本實驗室自行架設一套克爾光閘超快時間解析螢光(time-resolved fluorescence, TRFL)光譜系統，搭配自行撰寫的全自動數據擷取程式探討電子給體-受體(electron donor-acceptor, EDA)錯合物之電子轉移動力學，並提出可能的動力學模型。本篇論文中主要研究具有高游離能的非甲基取代苯與四氰基乙烯(TCNE)形成錯合物於二氯甲烷及四氯甲烷溶劑中的電子轉移動力學，並搭配實驗室學長姐的多甲基取代苯-TCNE錯合物的研究成果作討論，探討一系列由低放熱到高放熱的電子轉移動力學過程。我們藉由測量靜態吸收光譜及螢光光譜來獲得電荷轉移的吸收譜帶及放光波長，進而選擇適當的激發波長及偵測波長範圍，以觀察激發態錯合物的時間解析螢光光譜。我們以總體放光強度(P(t))隨時間的變化來分析錯合物的動力學過程。簡單來說，錯合物受到雷射激發至激發態後，先經由快速的solvation、結構緩解、振動緩解及分子內轉換至較低的能態，接著在進行分子內的電荷再結合回到基態。在P(t)模型的模擬分析後，在二氯甲烷溶劑中，3種錯合物皆可獲得3個時間常數分別為< 0.2 ps (solvation、IC)、~5 ps (non-equilibrium ET)及差異較大的charge recombination(CR)速率(PhCl-TCNE：45 ps、PhF-TCNE：21 ps、PhCN-TCNE：29 ps)；在四氯化碳溶劑中，5種錯合物皆可獲得2個時間常數分別為< 1.5 ps (solvation、IC)及差異較大的CR速率(PhCl-TCNE：580 ps；PhF-TCNE：470 ps；p-TN-TCNE：210 ps；PhCN-TCNE：140 ps；ClPhCN-TCNE：280 ps)。於兩種溶劑中的CR會有如此的差距來自於solavtion效應的影響。在低放熱(多甲基取代苯-TCNE)至高放熱(本篇論文研究之錯合物)的電子轉移速率中，我們發現Marcus theroy模型無法預測的double-inverted現象，亦即CR速率再次隨著-ΔG0的增加而變快。我們引用Intersecting state model(ISM)搭配Marcus theroy來解釋double-inverted region形成的原因：在大量放熱的反應中，錯合物的結構會因此產生較大變化，導致reaction coordinate上之平衡位置也會改變，進而造成CR速率再次變快。

關鍵字

動力學；電子轉移；電子給體-受體錯合物

並列摘要

Ultrafast dynamics of substituted benzene-TCNE complexes in two solvents (CH2Cl2, CCl4) was investigated in ultrafast time-resolved fluorescene (TRFL) spectrometer implemented by optical Kerr gating (OKG). We used femtosecond laser to excite the non-methyl substituted benzene-TCNE complexes to CT states, and the resulting TRFL spectra were measured. We used the total fluorescene (P(t)) to analyze the result which reveal complexes relaxations associated with charge recombination(CR). We found different decay behaviors in different solvents. The fastest component in the similar time scale (<0.2 ps) for three complexes (chlorobenzene(PhCl)-TCNE、fluorobenzene(PhF)-TCNE、benzonitrile(PhCN)-TCNE) is assigned to CT2→CT1 transition and the slowest component is ascribed to CR. The CR time constant in CH2Cl2 for PhCl-TCNE、PhF-TCNE、PhCN-TCNE are 45, 21 and29 ps, respectively. The CR time constant in CCl4 for PhCl-TCNE、PhF-TCNE、Tolunitrile-TCNE、PhCN-TCNE、4-chlorobenzonitrile-TCNE are 580, 470, 210, 140 and 280 ps, respectively. We concluded that no matter which solvents we used, CR time constants of methylbenzene-TCNE complexes are consisted with the behavior in the Marcus inverted region. However, the others violate the behavior. We use the intersecting state model (ISM) which accounts for structural relaxation of complex that the Marcus theory doesn’t consider to explain this unexpected behavior.

並列關鍵字

Dynamics ； Electron transfer ； EDA complex

參考文獻

1. Marcus R.A.; Sutin N., Biochim. Biophys. Acta 1985, 811, 265–322.

2. Jortner, J.; Bixon, M. , Prigogine, I.; Rice, S. A., Advances in Chemical Physics, Volume 106, Part 1: Electron Transfer -- From Isolated Molecules to Biomolecules, New York, 1999.

6. Wasielewski, M. R., Chem. Rev. 1992, 92, 435–461.

9. Heeger, A.J.A., Chem. Soc. Rev. 2010, 39 2354–2371.

10. Dimitrov, S. D.; Bakulin,A. A.; Nielsen, C. B.; Schroeder, B. C.; Du, J.; Bronstein, H.; McCulloch, I.; Friend, R. H.; Durrant, J. R., J. Am. Chem. Soc. 2012, 134, 18189–18192.

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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

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