研究4-苯胺基反式雙苯乙烯及其衍生物與4-二甲基氨基苯乙烯―矽烷基―反式雙苯乙烯共聚物單體在不同溶劑中之激發態動力學

我們使用時間解析光譜以及理論計算研究4-苯胺基反式雙苯乙烯及其衍生物(trans-4-(N-arylamino)stilbenes, p1H, p1CN 及p1OM)及4-二甲基氨基苯乙烯―矽烷基―反式雙苯乙烯共聚物單體(4-((E)-2-(dimethyl(4-((E)-styryl)phenyl)silyl)vinyl)-N,N-dimethylaniline)之溶劑效應並提出其光激發動力學模型，我們使用時間相關單光子計數器與飛秒瞬態吸收光譜配合理論計算來研究這些分子在不同的溶劑中的激發態特性。苯胺基雙苯乙烯及其衍生物經330 nm光激發到Franck-Condon區域後，會很快的產生電荷轉移到PICT能階平衡位置，時間常數約為0.5~1.8 ps。到了PICT能階後，p1H只會經由放出螢光或是光異構化回到基態，其光異構化的生命期約在10 ps~120 ps，其生命期由溶劑的極性與黏度決定；p1CN與p1OM則是除了放出螢光與光異構化外，在極性環境中，可經由單鍵扭轉成TICT，其中p1CN生成TICT能態的時間常數約為5 ps~30 ps，而p1OM則約為4 ps~30 ps，視溶劑的黏度與極性而定。隨著溶劑的極性上升或是黏度下降，其所需要跨越的能障越低，也越容易生成TICT能態。對於醚類的環境下發現的τ3異常拉長的現象，我們認為在中低極性的環境下，在PICT與TICT能態間的能量相較於高極性的環境中來的接近，因此兩能態間會形成耦合的狀態，因而拉長了在中低極性環境中的生命期。在醇類溶劑僅的氫鍵會連結到p1CN的腈基上，產生氫鍵效應，使其生命其比p1H與p1OM更短。另外，p1OM之激發態生命期較p1CN短，我們認為其TICT能態也會在雙苯乙烯的雙鍵上發生光異構化反應。另外，對於4-二甲基氨基苯乙烯―矽烷基―反式雙苯乙烯共聚物單體之實驗結果顯示此分子在非極性環境下，在極短時域時，能量會快速的由雙苯乙烯端傳遞到苯胺端(~1 ps)，接著由苯胺端21ππ*能態與11ππ*能態藉由緩解回到基態，其生命期分別約為65 ps以及2 ns。在極性的環境下，除了上述的過程外，另外尚有電荷由苯胺端轉移到雙苯乙烯端的電荷轉移途徑，其效率約為0.75 ps，並且最終藉由電荷再結合回到基態。此分子在極性溶劑中，在延遲時間中期，光譜呈現明顯的藍位移現象，並且隨著溶劑黏度上升，其藍位移生命期隨之上升，我們認為此現象為目標分子產生一單鍵旋轉，使系統中之電荷轉移能態大部分轉換為syn構形。

關鍵字

超快雷射光譜；動力學

並列摘要

We have studied the trans-4-(N-arylamino)stilbenes (p1H, p1CN, and p1OM) and 4-((E)-2-(dimethyl(4-((E)-styryl)phenyl)silyl)vinyl)-N,N-dimethylaniline by using time-resolved spectra and performed calculations based on density functional theory. The arylaminostilbenes relaxed to the equilibrium position of the planar intramolecular charge transfer (PICT) state from the Franck-Condon region in 0.5-1.8 ps. Then, p1H emitted fluorescence or underwent isomerization back to the ground state. The time constant of the isomerization process is about 10-120 ps varied with solvents viscosity and polarity. In polar solvent, p1CN and p1OM underwent twisting a single bond to reach the TICT surface; the time constant of this conversion is 5-30 ps for p1CN and 4-30 ps for p1OM. The third temporal component shows abnormal elongation lifetime in ether solvents. We propose that the PICT and the TICT states are close in energy and electronically coupled resulting in mixing the TICT character in PICT state. Molecule p1CN exhibits the hydrogen-bond effect according to the observed short lifetimes in alcohols. Moreover, p1OM may undergo isomerization in the TICT surface because the measured lifetime is five-times shorter than that in p1CN. For 4-((E)-2-(dimethyl(4-((E)-styryl)phenyl)silyl)vinyl)-N,N-dimethylaniline, the energy was transferred rapidly ~1 ps from the stilbenyl moiety to the aminostryenyl upon photoexcitation at 266 nm. Then the excited aminostryenyl in either 21ππ* state or 11ππ* relaxed to the ground state in 65 ps and 2 ns, respectively. In the polar environment, the charge transfer process occurred; the charge migrated from aminostryenyl to stilbenyl in 0.75 ps, then relaxed to the ground state by the charge recombination. In polar solvents, the transient absorption band of the charge transfer state peaked at 530 nm shows blue shift; the time constant of the blue shift becomes increased with solvent viscosity indicating structural variation in this process. We propose that the molecule in the charge-transfer surface changed the conformation from the anti to the syn form.

並列關鍵字

ultrafast ； molecular dynamic

參考文獻

21. Lewis, F. D.; Kalgutkar, R. S.; Yang, J.-S., The Photochemistry of trans-ortho-,-meta-, and -para-Aminostilbenes. J. Am. Chem. Soc. 1999, 121, 12045-12053.

1. Waldeck, D. H., Photoisomerization dynamics of stilbenes. Chem. Rev. 1991, 91 , 415-436.

2. Herkstroeter, W. G.; McClure, D. S., Lowest triplet state of stilbene. J. Am. Chem. Soc. 1968, 90 , 4522-4527.

3. Dainton, F.; Robinson, E. A.; Salmon, G. A., Pulse radiolysis of solutions of stilbene. I. Evidence for triplet and singlet excited state formation. J. Phys. Chem. 1972, 76, 3897-3904.

4. Lewis, F. D.; Simpson, J. T., Intersystem crossing in stilbene exciplexes. J. Phys. Chem. 1979, 83, 2015-2019.

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研究4-苯胺基反式雙苯乙烯及其衍生物與4-二甲基氨基苯乙烯―矽烷基―反式雙苯乙烯共聚物單體在不同溶劑中之激發態動力學

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