系統性設計並合成具備非典型多重放光之單分子發色團

Abstract

時至今日，應用於有機發光二極體, 生醫影像, 螢光探針...等等的有機發色團 層出不窮，有系統地開發此類有機分子漸顯重要。為了符合應用上的需求，各式各 樣用來設計相對應有機發色團的策略已被研究報導。然而，在這些策略當中，以雙 重放光訊號和大斯托克斯位移為目標的分子設計概念至今仍不常見。特別是，涉及 兩種不同激發態電子能階的雙重螢光放光現象，僅能在為數不多的有機分子中進 行激發態光反應後被觀察到。而截至目前為止，光反應被統整歸納為四大類，如: 激發態雙體(Excimer formation)、激發態分子內質子轉移(ESIPT)、扭轉分子電荷轉 移(TICT)以及相對離子遷移反應。對這四類光反應機制進行基礎研究後，我們分別 合成了一系列 ESIPT 分子以及相對離子遷移分子，並且在接下來的三個章節中， 深入探討這些分子的光物理性質以及光譜動力學。 在第一章中，我們合成出一系列鄰胺苯甲酸衍生物，此類分子因為具備氨基型 分子內氫鍵，滿足 ESIPT 反應條件。因此，我們可以在部分衍生物中觀察到雙重 螢光放光訊號。然而，基於上轉換螢光光譜儀的收光範圍限制，我們無法收到直接 的螢光生命週期數據，來對此 ESIPT 行為進行動力學探討。為了善用此類鄰胺苯 甲酸衍生物，由分子結構觀點來看，這類衍生物因為具備羧酸基團和氨基團，所以 同時具有酸和鹼的兩性特質，我們應用其作為雙功能性的基質，配合基質輔助雷射 脫附/游離飛行時間式(MALDI-TOF)質譜成像技術，對小鼠腦部內的細微構造進行 顯像。 在第二章中，我們成功合成出一系列直線型 D--A 系統的甲基吡啶鹽類分子， 此類分子由於具備不同的相對陰離子，我們在低極性溶液中觀察到非典型的多重 放光(multiple emission)訊號。接著，根據其陰離子大小、陽離子本體長度以及不同 溶劑環境下的黏滯性，我們建立了一套照光誘導陰離子遷移的反應機制，用以解釋 這一系列鹽類分子的多重放光現象。 在第三章中，有鑒於甲基吡啶鹽類分子能夠在低極性溶液中進行離子遷移反 應，進而產生多重放光現象。為了拓展離子遷移反應的研究，我們另外合成了一系 列新穎的甲基吡啶鹽類分子，這些鹽類的分子結構中由於修飾上嗎啉基團，具備分 子內氫鍵。我們期望在 ESIPT 反應的誘導下進行電荷轉移(charge transfer)後觀察到 這些鹽類分子的離子遷移行為。

At the present time, the research related to fabricate chromophores based on the rational design at molecular level is central importance because of its applications in OLEDs, bioimaging, medicine, fluorescent probes, etc. To meet the growing demands, various strategies have been created to design the chromophores accordingly. Over the last few decades, organic chromophores displaying dual emission and large Stokes shifts still remain uncommon to date. In particular, the dual fluorescence emission is a rare photophysical phenomenon observed in very few organic chromophores in which a two- color radiative process occurs that involves two distinct excited electronic states. So far, the observation of dual fluorescence emission was linked to electronic rearrangement of an excited fluorophore, which led to two conformers with distinct emissive properties. The well-known photoreactions, resulting in dual fluorescence emission, are listed as follow: excimer formation, excited-state intramolecular proton transfer (ESIPT), twisted intramolecular charge transfer (TICT) and counterion migration. In chapter 1, a novel series of amino-type intramolecular hydrogen-bonded molecules derived from the core chromophore anthranilic acid have been synthesized to investigate the associated R-N-H···O=C proton transfer properties in the excited state. Unfortunately, the current instrumental set prohibits the further fluorescence up- conversion measurements on the emission from the normal from of compound CHO- NHAc. Under this circumstance, there are no direct fluorescence lifetime evidence to ensure their ESIPT behavior. But, even so, from the viewpoint of chemistry, these anthranilic acid derivatives are endowed with acid/base bifunctional properties and can be promised to be the candidate for dual polarity matrix which is applied in MALDI mass spectrometry. In chapter 2, we successfully developed a new series of linear D--A-type methylpyridinium salts with different lengths of a spacer and counter anions. These ionic species exhibit anomalous multiple emission in toluene and led us to propose a counterion migration mechanism induced by excited-state charge transfer in weakly polar and nonpolar solvents. In this mechanism, the dynamics depend on the size of the counterions, the length of spacer, the dipole moment of the charge separation, and the environment viscosity. In chapter 3, counterion migration of methylpyridinium fluorophores have shown abnormal multiple emission in weakly polar and nonpolar solvents. We present a new system based on the use of ESIPT to achieve efficient counterion migration without relying on the well-established donor-acceptor scheme. In an appropriately designed morpholine-based molecule with intramolecular hydrogen bonding, ESIPT process following by intramolecular charge transfer (ICT) leads to formation of a morpholinium tautomer, resulting in counterion migration from methylpyridinium to morpholinium. Thus, multiple emissions from single ESIPT-based ion migratory compound will be come true.