紫質在溶液中、生物與奈米環境下的光譜與緩解動力學研究

Abstract

本論文利用時間相關單光子技術與飛秒螢光上轉移技術來研究紫質分子在溶液中與固相薄膜上的緩解動態學。在液相溶液中的紫質分子之研究，主要為ZnBPP和H2BPP 及其溴化物衍生物。ZnBPP 在S1 態的緩解過程可以分成兩種，第一種屬於高能態緩解過程，另一種為低能態的緩解過程。高能態的緩解過程主要發生在540-570 nm 的螢光光區，而低能態的緩解則發生在580 nm 以後的光區。對於溴化鋅離子的紫質與原紫質分子的研究，我們發現分子內的重原子效應會影響S2 與S1能態上的緩解過程或Qx 態上的分子內振動能重新分配與其他的振動弛緩過程。另一方面，ZnPP 在緩衝溶液中易形成聚集體，其在S1 能態的緩解過程的生命期小於100 fs，但ZnPP-Mb 錯合物生成，則因蛋白質使得ZnPP 免於在緩衝溶液中產生聚集體，而觀測到ZnPP 單體在蛋白質中的S1 能態的緩解過程。因ZnPP-Mb 激發後的振動能量易使蛋白質改變本性，由α 螺旋結構變成鏈型結構，而使得內部的ZnPP裸露在緩衝溶液中，故我們亦觀測到部分聚集體的衰減過程。 在固相中的研究則以ZnCA(PE)1-4BPP 與ZnCATPP 為主，此分子利用羧基化學吸附在TiO2 的奈米粒子上。因為紫質分子易在固相薄膜中產生聚集體，故我們利用大量的PMMA 聚合物來使紫質分子均勻地分散在聚合物中，其所測得的結果與在溶液中的緩解過程相似。當紫質分子直接塗布在玻璃上時，其螢光瞬態光譜顯示有兩組去激化過程，其主要以J-聚集體猝滅為主。若紫質分子吸附在二氧化鈦奈米晶相薄膜上時，其光譜訊號衰減速率變快，因為其過程中包含了介面電子 轉移過程。此外我們亦發現紫質分子與二氧化鈦之間的介面電子轉移過程包含經由化學鍵傳遞或經由空間穿遂的方式來達成。經由化學鍵的介面電子轉移與紫質分子上π電子是否為定域化有關，而空間穿遂的電子轉移則與激發電子的能態和聚集體或分子與二氧化鈦粒子間的距離有關。

The excited-state relaxation dynamics of zinc and free-base porphryins in solutionsand on solid films were measured with time-correlated single photon counting and femtosecond fluorescence up-converted techniques. ZnBPP, H2BPP and its bromides were studied the dynamics of the excited states in solution. The relaxation processes of the S1 excited state of ZnBPP involve two types of relaxations. One is due to the hot-relaxations which were obtained at 540-570 nm and another is due to the cold-relaxations which were obtained above 580 nm. We also found intramoleuclar heavy-atom effect that affects relaxations of the S2 and S1 excited states in zinc bromo-porphyrins. In addition, the intramoleuclar heavy-atom effect also influences the intramoleuclar vibrational energy redistribution and other relaxations of the Qx excited state for free-base bromo-porphyrins. Besides ZnBPP and its derivates, we also measured fluorescence transients of ZnPP-Mb in buffer solution. The transients show two components of relaxations, one component is contributed to a unfolding protein which enables a ZnPP molecule to form H-aggregate and another component is contributed to the relaxations of a folding ZnPP-Mb complex. ZnCA(PE)1-4BPP and ZnCATPP were studied on solid films. To avoid aggregating, we used a lot of PMMA polymers to mix with zinc porphyrins. The transients of ZnCAPEBPP/PMMA show the dynamics which is like that in THF. However, the transients of porphyrin/glass are different from that in THF or PMMA. The relaxations of porphyrin/glass are assigned to H- and J-aggregation quenchings, but the major quenching is J-aggregates. According to the transients of porphyrin/TiO2, the interfacial electron transfers (IET) are complicated. The interfacial electron transfer contain two ways that are through chemical bond or space tunneling. IET by way of chemical bond is concerned with the delocalized π electrons on porphyrin, however, IET by way of space tunneling is concerned with the distance between porphyrin and TiO2 and the energy of an excited electron.