3-hydroxy-2-(thiophen-2-yl) chromen-4-one及其衍生物之 激發態分子內質子轉移

Abstract

利用穩定態(steady-state)吸收和螢光光譜、飛秒級螢光合頻法(femtosecond fluorescence upconversion)研究3-hydroxy-2-(thiophen-2-yl)chromen-4-one(3-HTC)及其衍生物在溶劑中的激發態分子內質子轉移(ESIPT)的光譜和動力學機制。在這邊我們設計了將3-hydroxy flavone 中2號位苯環取代成2號位的噻吩(thiophen-2-yl)及一系列的衍生物(3-HTC)，其中3-HTC分子內的噻吩上的5號位取代成2-methylenemalononitrile的分子(3-HTC-diCN)，在溶劑為苯及二氯甲烷中，可以明顯的發現激發在不同波長的螢光光譜，標準態(normal form)和異構態(tautomer form)的兩特徵放射的比例不同，利用時間相關單一光子計數(Time-correlated single photon counting )方法觀測期生命期，發現其標準態和異構態在激發態時不為平衡，於是我們利用飛秒級螢光合頻法(femtosecond fluorescence upconversion)對其激發態的動力學做更深入的研究，發現其激發在350nm及425nm 對於標準態的特徵放射中，其隨著溶劑碰撞緩解(solvent relaxation)並做ESIPT的衰減速度分別為1.5 ps及2.7 ps，由此可知ESIPT分子在激發到更高的激發態時，具有更快的ESIPT速度。

3-HTC-DiCN and 3-HTCA, the derivatives of 3-Hydroxy-2-(thiophen-2-yl) chromen-4-one(3-HTC) , they are the first two examples to observe the rate of ESIPT (Excited-State Intramolecular Proton Transfer ) are excitation wavelength dependent. At steady state emission spectra, we can see the ratio of normal form and tautomer form’s emission depends on excitation wavelength. By time-correlated single photon counting method, we observed the normal form and tautomer form are not equilibrium at excited state. So we use femtosecond fluorescence up-conversion to observe the excited state dynamic rate, the ESIPT with solvent relaxation rate are 1.5ps and 2.7ps when excite at 350nm and 425nm. By the result of these measurements, the ESIPT rate is excitation wavelength dependent.