第一部分 7-胺基奎寧衍生物之激發態分子間質子轉移 的合成與研究 第二部分 1-胺基-7-氮雜吲哚衍生物之激發態平面化 分子內電荷轉移的合成與研究

Part I: Synthesis and Study of Excited-State Intermolecular Proton Transfer in 7-Aminoquinoline and its Derivatives Part II: Synthesis and Study of Planarized Intramolecular Charge Transfer in 1-Amino-7-azaindole and its Derivatives

劉穎瑄(Ying-Hsuan Liu)

指導教授 ： 周必泰

國立臺灣大學/理學院/化學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201801847

摘要

在第一章節中，我們想探討分子激發態質子轉移的反應機制，透過合成出的7AQ以及其他在胺基上具有推拉電子基團的衍生物來做光物理的研究。由於7AQ系列化合物的質子接受端與給予端距離遙遠，需透過溶劑當介質才能進行激發態質子轉移的反應。在使用甲醇當溶劑的分子光譜中，我們發現只有接上拉電子基團的TFA-7AQ、Ts-7AQ、Boc-7AQ以及Ac-7AQ有產生激發態質子轉移，但是接上不同強度的拉電子基團的分子進行激發態質子轉移的速率卻是相近的，這結果發現與我們實驗室之前對於分子內激發態質子轉移反應的研究結果並不同；然而，透過在水中的酸鹼滴定測量，我們發現胺基上接著的推拉電子基不僅會改變質子給予端的酸度，同時也會透過共軛效應去變化質子接受端的鹼度，因此造成分子間激發態質子轉移速率近似的結果。
在第二章節中，我們想討論由扭曲型分子內電荷轉移延伸出的平面化分子內電荷轉移的反應機制，透過合成的7AI以及其衍生物diMeN-7AI及AcNH-7AI來進行光物理性質的檢測：在以環己烷當溶劑的量測中，我們發現7AI跟diMeN-7AI的吸收與放光具有130 nm、158 nm的大範圍位移以及高放光效率，印證分子在激發態有進行平面化的構型變化，然而AcNH-7AI卻是分別在323 nm及380 nm放出螢光，推測是只有部分完成了平面化的過程，其他則是以原構型放出螢光；另外，我們也在乙腈中量測光譜，7AI跟diMeN-7AI的吸收峰與紅移的放出峰具有210 nm、230 nm的更加大範圍位移，而AcNH-7AI則是變成單一螢光在420 nm的位置。由於環己烷為非極性溶液，分子無法在之中進行分子內電荷轉移，因此我們認為平面化分子內電荷轉移的機制為：當分子受激發時傾向旋轉單鍵，透過平行的胺基孤對電子對以及芳香環的π電子讓分子電荷分佈可以更游離，以降低分子在激發態時的能量。然而，由於乙醯基的結構較大、環己烷的粘性也較大，才導致AcNH-7AI在環己烷中無法完全順利翻轉成平面化的構型。

關鍵字

激發態分子間質子轉移 ； 胺基類激發態分子間質子轉移 ； 推拉電子基 ； 激發態平面化分子內電荷轉移 ； 大斯托克斯位移

並列摘要

Part I
7-Aminoquinoline (7AQ) and its amino derivatives have been designed and synthesized to study their possible excited-state proton transfer (ESPT) reaction. Due to the far separation between the proton donor NR-H (D) and acceptor –N (A) sites, ESPT in 7AQ and analogues, if available, should proceed with solvent catalysis process. As a result, assisted by solvent molecules, TFA-7AQ, Ts-7AQ, Boc-7AQ and Ac-7AQ undergoes ESPT in alcohols such as methanol. Systematically probing ESPT spectroscopy and dynamics among all NR-H derivatives has been carried out in methanol. However, unlike the NR-H intramolecular system where the rate of excited-state intramolecular proton transfer (ESIPT) increases as increasing the NR-H acidity, the rate of solvent catalyzed ESPT was found to lack correlation with respect to the NR-H acidity among all NRH derivatives. The results are rationalized by the fact that increase of the NR-H acidity by the stronger electron withdrawing R group concurrently decreases the basicity of the quinolone nitrogen via resonance inductive effect.

Part II
In an aim to explore the mechanism of planarized intramolecular charge transfer (PLICT), we have synthesized 1-amino-7-azaindole (NH2-7AI) and N-amination derivatives, diMeN-7AI and AcNH-7AI. Because amino group is twisted in the ground states and becomes planarized in the excited states, this provides a powerful method to tune a very large Stokes shift and simultaneously emit high quantum yields in molecular spectroscopy. Measured in cyclohexane, apolar solvent, NH2-7AI and diMeN-7AI were investigated the large Stokes shifts amounting to about λ = 130 nm and 158 nm. This phenomenon can be rationally interpreted that in the excited states N-substituent molecules tend to delocalize electronic distribution via the lone pair electrons on nitrogen. Once the nitrogen lone pair electrons are coupled with aromatic π electrons through planarization, the molecules can potentially decrease excited-state energy. On the other hand, AcNH-7AI depicted a dual emission in cyclohexane at 323 nm and 380 nm, which could be implied as vertical state and planar state. In acetonitrile, polar solvent, AcNH-7AI was observed a large Stokes shift at 420 nm, progressing PLICT. Obviously, acetyl group is larger than dimethyl group, and the value of viscosity of cyclohexane is higher than that of acetonitrile, which results in the hinder of planarization. It is notable, consequently, that the size of substituent and viscosity of solvent are also the key elements of PLICT.

並列關鍵字

Excited-State Proton Transfer Reaction ； Amino-Type Excited-State Intermolecular Proton Transfer Reaction ； Electron Donating/Withdrawing Group ； Planarized Intramolecular Charge Transfer ； Large Stokes Shift

參考文獻

Part 1.

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