質子/電子轉移之光譜與飛秒雷射動力學—研究與探討

質子與電子轉移無論是生物體內或是一般的化學反應中都扮演了重要的角色，本篇論文的主要研究課題是根據著名質子轉移分子2-(2’-hydroxy) benzoxazole (HBO) or 2-(2’-hydroxy) benzothiazole (HBT) 設計出一系列同時具有質子與電子轉移特性的衍生物。利用不同的光譜技術來探討質子與電子轉移間的關係。論文的第一章裡將基本的光化學反應機制做了大致的簡介。基態電子被光子激發後的緩解途徑：分為光緩解與非光緩解。光緩解途徑從緩解的激發態能階可分為螢光與磷光；非光緩解途經可分為物理性質的由光能轉為熱能散失在系統中，或是化學性質的由光能轉為化學能進行化學反應；並以簡單文字與圖形簡述質子與電子轉移的相關原理。論文的第二章介紹一個電子轉移誘導質子轉移分子系統在不同極性的溶劑條件下的反應變化，實驗技術從基態的吸收、螢光光譜分析到飛秒雷射的單光子技術與變溫實驗，並利用理論計算與實驗結果對照，可詳細明白此系統中的動力與熱力變化。一開始研究此系統的目的在於尋找Marcus Theory中的反轉點 (Inverted region)，但實驗證明在此系統中無法得到想要結果。論文的第三章接續第二章的結果進行延伸，設計一質子誘導電子轉移分子系統。由於質子的質量相較於電子來的大；轉移的速度亦電子遠大於質子；因此可將整個系統視為一質子與電子同步轉移的系統來加以分析。利用上述的實驗技術可明白在此系統內有可能達到Marcus Theory中的反轉點 (Inverted region) ；不過受限於實驗儀器的偵測範圍限制，仍然無法得到一明確結果。不同於其他系統中的質子與電子轉移反應，利用此系列中的延伸系統可發現更多隱藏背後的物理意義，對於了解質子與電子轉移反應有更大的助益。

關鍵字

質子/ 電子轉移；飛秒雷射動力學

並列摘要

Studies of excited state intramolecular proton transfer (ESIPT) coupled with charge transfer (ESICT) are presented here. As for a strategic design, we synthesized a series of derivatives based on the famous ESIPT molecules 2-(2’-hydroxy) benzoxazole (HBO) or 2-(2’-hydroxy) benzothiazole (HBT). In HBO and HBT, the lone pair electrons at the nitrogen atom have been incorporated into the resonance, i.e. the construction of aromaticity, such that its electron donating property, comparing with those of alkyl amines, is negligibly small. Upon Franck-Condon excitation, one can thus perceive its lack of ESICT. Instead, ESIPT takes place, forming a proton transfer tautomer, in which the central nitrogen atom acts as the secondary alkyl amine. If the para-position of the nitrogen is anchored by a strong electron withdrawing group, ESICT should proceed simultaneously at every moment ESIPT takes place. In other words, one can envisage such types of reaction as the photon induced ESICT associated with a nuclear (proton) motion, rendering an ideal system to study the role of solvent polarity for the ESICT/ESIPT coupled reaction, and hence a paradigm to test the “Marcus theory (modified by Hynes et al.) based on the proton transfer reaction. Although di-CN group is an electron acceptor anchored on the para position of the center nitrogen atom in diCN-HBO and diCN-HBT, the distance between di-CN group and hydroxy group is long enough to prevent affection in the ground state. Started by Franck-Condon excitation, the ESIPT takes place first to create a chance for electron delocalization. As electron motion is faster than nuclear motion, ESICT is initiated and finished during ESIPT. For ESIPT and ESICT is correlated, the combination rate is solvent polarity dependent. The enol form decay rate of diCN-HBO decreases with increasing solvent polarity. The phenomena provides us an ideal model different from our preceding proton transfer compounds such as 4’-(Dialkylamino)-3-hydroxyflavone, p-N,N-Ditolylaminosalicylaldehydes,and HABT, etc.

並列關鍵字

Proton / Charge transfer ； Spectroscopy and Femtosecond Dynamics

參考文獻

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質子/電子轉移之光譜與飛秒雷射動力學—研究與探討

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