激發態質子轉移之基礎研究與應用

The fundamental research and application of excited-state proton transfer molecules

陳怡安(Yi-An Chen)

指導教授 ： 周必泰

國立臺灣大學/理學院/化學研究所/博士(2017年)

https://doi.org/10.6342/NTU201800061

摘要

第一章 環住的綠色螢光蛋白衍生物之分子內激發態質子轉移的光物理研究
此篇論文最主要是利用有機合成的方式，成功的合成出非天然的綠色螢光蛋白(GFP)，p-LHBDI及其鄰位衍生物 o-LHBDI, 並且和出H2BDI, 同時具有對位和鄰位羟基，使得化合物的旋轉運動已被部分限制。o-LHBDI具有雙鎖定配置，即七圓環氢键和五圓環C（4-5-10-13-14）環化，從中發生激發態分子内質子轉移，產生了極高的螢光量子產率（0.18在甲苯中）和產生自發性放大放射。與其解鎖的對應物相比，在水中陰離子形式的p-LHBDI和H2BDI也觀察到螢光產量顯著增加，因此根據其化學和光譜學方面充分討論了結構與發光關係。在固體中，o-LHBDI表現出H型聚集體分子性質，提供窄頻寬放光，並且已經成功應用於製造黃色有機發光二極體（λmax= 568nm，ηext= 1.9％）。

第二章 探討一系列氨基型分子的激發態分子內質子轉移反應之光物理性質研究
設計並合成了一系列包含2-(2’-aminophenyl)-benzothiazole衍生物的新型氨基（NH）型氫鍵（H-boding）化合物。與羥基（OH）型氫鍵體係不同，其中一個氨基氫可以用推/拉電子基取代。利用修飾不同官能基研究氨基型激發態分子內質子轉移（ESIPT）的綜合光譜和動力學，此羥基型ESIPT系統在以前是無法研究的。改變氫鍵強度（N-H鍵距離和質子酸度），並且觀察到在ESIPT中動力學和熱力學之間的相關性，證明更強的N-H ... N氫鍵導致更快的ESIPT的趨勢，如實驗觀察，熱力學反應較為明顯。並且，ESIPT反應可以首先從禁止到達到可測量的ESIPT速率的平衡。

第三章 具有N-H七元環分子內氫鍵化合物的激發態質子轉移的光物理研究
實驗室成功合成出一系列含有5-(2-aminobenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one（o-ABDI）作為核心螢色團的化合物，其具有N-H型的七元環分子內氫鍵。可以通過用取代基R代替氨基氫原子中的一個氨基氫原子來酸化NH質子的酸度，隨著R的吸電子強度的增加使酸度增加，即H < COCH3 < COPh < Tosyl < COCF3。Tosyl和COCF3衍生物經歷超快，不可逆的激發態分子內質子轉移（ESIPT），其導致僅得到在紅色區域的質子轉移放光。對於COCH3和COPh取代的對應物，涉及正常和質子轉移互變異構體的可逆ESIPT，因此可得到兩種放光。對於具有最弱酸性的o-ABDI，由於其高度反應性，ESIPT被禁止。結果清楚地表明了通過改變七元環分子內氫鍵和體系中的質子酸度和氫鍵強度來實現ESIPT的利用。對於所有研究的化合物，螢光量子產率皆弱（約10-3），但在固體中其螢光量子產率範圍為3.2至47.4％。

第四章 激發態分子內質子轉移（ESIPT）反應的可逆性的控制：在新的Thiazolo[5,4-d]thiazole ESIPT體系中調控主發光體的極性產生白色有機發光二極管的光物理研究及應用
通過使用thiazolo[5,4-d]thiazole（TzTz）部分作為質子受體核心，化合物2,2’-(thiazolo[5,4-d]thiazole-2,5-diyl)bis(4-tert-butylphenol)（t-HTTH）和4-tertbutyl-2-(5-(5-tert-butyl-2-methoxyphenyl)thiazolo[5,4-d]thiazol-2-yl)-phenol（t-MTTH）已經被策略性地設計和合成。在光激發下，t-HTTH和t-MTTH均經歷可逆型激發態分子內質子轉移（ESIPT），其基礎機理已經通過各種溶劑中飛秒早期鬆弛動力學證實。在激發態的預平衡過程使其產生正常（~ 440nm）和質子轉移互變異構體（〜 560nm）放光，強度比取決於周圍介質的分子結構和極性。另外，放光可以從藍光一路調節至黃光。t-MTTH成功製作了白色有機發光二極管（WOLED），其L'Oreairage坐標為（0.29,0.33），並且外部量子效率（ηext）為1.70％。更重要的是，電致發光光譜顯示出卓越的顏色穩定性。該結果首次證明了基於單分子ESIPT反應的可信WOLED，這可能對實際應用具有深遠的影響。

第五章 利用熱激活延遲螢光(TADF)儲存分子能量
展示熱激活延遲熒光（TADF）的分子具有位於最低激發單重態（S1）和三重態（T1）狀態之間的近端能量水平。因此，一旦知道S0→S1吸收或S0←S1發射間隙，就可以容易地評估它們的T1能階。這有利於利用TADF分子的三重態作為能量轉移的敏化劑的應用。在此我們利用一個熱激活延遲熒光（TADF）的分子phenoxazine–triphenyltriazine (PX-TZ)搭配上norbornadiene (NBD), (1s,4s)-bicyclo[2.2.1]hepta-2,5-diene,形成有效的儲能二元PXTZ-NBD。PXTZ-NBD表現出最佳的吸收，涵蓋高達460 nm的太陽光譜。在激發PXTZ-NBD後，PXTZ作為敏化劑，通過三重態 - 三重態能量轉移使NBD三重態敏化，隨後將NBD轉化為quadricyclane system（QC），即tetracyclo[3.2.0.02,7.04,6]heptane，形成熱穩定的PXTZ-QC產物，另外，可通過催化反應迅速轉化為PXTZ-NBD。其獨特之處在於，利用TADF分子可直接監測光轉換和熱逆轉換的程度。 PXTZ-NBD ↹ PXTZ-QC光熱轉換使得能量存儲密度達到177 kJ / mol，經過五次光熱轉換循環後，具有良好的耐久性。這產生了一個基於TADF的太陽能熱能儲存系統，最佳的（≤ 460奈米）太陽能被收集。

關鍵字

激發太質子轉移

並列摘要

Chapter 1 Locked ortho- and para-Core Chromophores of Green Fluorescent Protein; Dramatic Emission Enhancement via Structural Constraint
We report the design strategy and synthesis of a structurally locked GFP core chromophore p-LHBDI, its ortho-derivative, o-LHBDI, and H2BDI possessing both paraand ortho-hydroxyl groups such that the inherent rotational motion of the titled compounds has been partially restricted. o-LHBDI possesses a doubly locked configuration, i.e., the seven-membered ring hydrogen bond and five-membered ring C(4-5-10-13-14) cyclization, from which the excited-state intramolecular proton transfer takes place, rendering a record high tautomer emission yield (0.18 in toluene) and the generation of amplified spontaneous emission. Compared with their unlocked counterparts, a substantial increase in the emission yield is also observed for p-LHBDI and H2BDI in anionic forms in water, and accordingly the structure versus luminescence relationship is fully discussed based on their chemistry and spectroscopy aspect. In solid, o-LHBDI exhibits an H-aggregate-like molecular packing, offers narrow-bandwidth emission, and has been successfully applied to fabricate a yellow organic light emitting diodes (λmax = 568 nm, ηext = 1.9%) with an emission full width at half-maximum as narrow as 70 nm.
Chapter 2 Harnessing Excited-State Intramolecular Proton-Transfer Reaction via a Series of Amino-Type Hydrogen-Bonding Molecules
A series of new amino (NH)-type hydrogen-bonding (H-bonding) compounds comprising 2-(2’-aminophenyl)-benzothiazole and its extensive derivatives were designed and synthesized. Unlike in the hydroxyl (OH)-type H-bonding systems, one of the amino hydrogens can be replaced with electrondonating/withdrawing groups. This, together with a versatile capability for modifying the parent moiety, makes feasible the comprehensive spectroscopy and dynamics studies of amino-type excited-state intramolecular proton transfer (ESIPT), which was previously inaccessible in the hydroxyl-type ESIPT systems. Empirical correlations were observed among the hydrogen-bonding strength (the N−H bond distances and proton acidity), ESIPT kinetics, and thermodynamics, demonstrating a trend that the stronger N−H•••N hydrogen bond leads to a faster ESIPT, as experimentally observed, and a more exergonic reaction thermodynamics. Accordingly, ESIPT reaction can be harnessed for the first time from a highly endergonic type (i.e., prohibition) toward equilibrium with a measurable ESIPT rate and then to the highly exergonic, ultrafast ESIPT reaction within the same series of amino-type intramolecular H-bond system.
Chapter 3 N-H-Type Excited-State Proton Transfer in Compounds Possessing a Seven-Membered-Ring Intramolecular Hydrogen Bond
A series of compounds containing 5-(2-aminobenzylidene)-2,3-dimethyl-3,5-dihydro-
4H-imidazol-4-one (o-ABDI) as the core chromophore with a seven-membered-ring N-H-type intramolecular hydrogen bond have been synthesized and characterized. The acidity of the N-H proton and thus the hydrogen-bond strength can be finetuned by replacing one of the amino hydrogen atoms by a substituent R, the acidity increasing with increasing electron-withdrawing strength of R, that is, in the order H < COCH3 < COPh < Tosyl < COCF3. The tosyl and trifluoroacetyl derivatives undergo ultrafast, irreversible excited-state intramolecular proton transfer (ESIPT) that results in proton-transfer emission solely in the red region. Reversible ESIPT, and hence dual emission, involving the normal and proton-transfer tautomers was resolved for the acetyl- and benzyl-substituted counterparts. For o-ABDI, which has the weakest acidity, ESIPT is prohibited due to its highly endergonic reaction. The results clearly demonstrate the harnessing of ESIPT by modifying the proton acidity and hydrogen-bonding strength in a seven-membered-ring intramolecular hydrogen-bonding system. For all the compounds studied, the emission quantum yields are weak (ca. 10-3) in dichloromethane, but strong in the solid form, ranging from 3.2 to 47.4 %.
Chapter 4 Control of the Reversibility of Excited-State Intramolecular Proton Transfer (ESIPT) Reaction: Host-Polarity Tuning White Organic Light Emitting Diode on a New Thiazolo[5,4‑d]thiazole ESIPT System
By using the thiazolo[5,4-d]thiazole (TzTz) moiety as the core of a proton acceptor, compounds 2,2′-(thiazolo[5,4- d]thiazole-2,5-diyl)bis(4-tert-butylphenol) (t-HTTH) and 4-tertbutyl-2-(5-(5-tert-butyl-2-methoxyphenyl)thiazolo[5,4-d]thiazol-2-yl)-phenol (t-MTTH) have been strategically designed and synthesized. Upon photoexcitation, both t-HTTH and t-MTTH undergo a reversible type excited-state intramolecular proton transfer (ESIPT), the underlying mechanism of which has been verified by femtosecond early relaxation dynamics in various solvents. The pre-equilibrium in the excited state leads to both normal (∼ 440 nm) and proton-transfer tautomer (∼ 560 nm) emissions, for which the intensity ratio is dependent on both the molecular structure and the polarity of surrounding media. As a result, the emission can be widely tuned from blue to yellow via white-light luminescence. On the basis of t-MTTH, a white organic light emitting diode (WOLED) was successfully fabricated, which achieved external quantum efficiency (ηext) of 1.70% with Commission Internationale de L’Eclairage coordinates of (0.29, 0.33). More importantly, the electroluminescent spectra show superior color stability that is independent of luminance. The result demonstrates for the first time a credible WOLED based on a unimolecular ESIPT reaction, which may have far-reaching implications for practical application.
Chapter 5 Molecular Energy Storage Exploiting Thermally Activated Delayed Fluorescence (TADF)
Molecules exhibiting thermally activated delayed fluorescence (TADF) possess proximal energy level between the lowest lying excited singlet (S1) and triplet (T1) states. Thus, the energy level of their T1 state can be readily assessed once knowing either S0 → S1 absorption or S0 ← S1 emission gap. This benefits application of TADF molecules utilizing the triple state as a sensitizer for energy transfer. On this basis, we report the new concept that utilizes a thermally activated delayed fluorescence (TADF) core phenoxazine–triphenyltriazine (PX-TZ) coupled with norbornadiene (NBD), (1s,4s)-bicyclo[2.2.1]hepta-2,5-diene, to form an efficient energy storage diad PXTZ-NBD. PXTZ-NBD exhibits an optimum absorption that covers the solar spectrum up to 460 nm. Upon exciting PXTZ-NBD, PXTZ serves as a sensitizer to sensitize NBD triplet state via triplet-triplet energy transfer, followed by the conversion of NBD to a quadricyclane system (QC), namely tetracyclo[3.2.0.02,7.04,6]heptane, forming a PXTZ-QC product that is thermally stable but convertible back to PXTZ-NBD promptly via catalytic reaction. The uniqueness lies in that the degree of photo-conversion and thermal-reverse-conversion can be directly monitored by TADF in both intensity and relaxation dynamics. The PXTZ-NBD ↹ PXTZ-QC photo-thermal conversion renders the energy storage densities of 177 kJ/mol with good durability evidenced by negligible side products after five photo-thermal conversion cycles. This generates a TADF based solar-thermal energy storage system, for which optimal (≤ 460 nm) solar energy is harvested.

並列關鍵字

excited state proton transfer

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