吸附在矽膠上的放光染料被氧氣焠滅的現象: 探討螢光和磷光反應機制的不同

Abstract

在本論文中，根據一系列以供體–pi共軛–受體為結構的有機鏻鹽化合物 (compound 1-3) 所放出的螢光在固態矽膠上被氧氣焠滅的現象，我們發現螢光在固態的強度會隨著氧氣濃度的增加而下降。實驗結果顯示1-3的螢光在矽膠上被氧氣焠滅的速率常數 (〖k_q^S〗_(obs.)) 的數量級大約落在1010 M-1s-1，與其在有機溶劑中的速率常數數量級相同，另外的研究則發現磷光在固態被氧氣焠滅的速率常數 (〖k_q^T〗_(obs.)) 大致上比 〖k_q^S〗_(obs.)小兩個數量級。深入探討後我們了解到這樣的差異源自於氧氣與染料分子形成碰撞複合體之後的內在的速率常數 (〖k_q^S〗_(intr.) 和 〖k_q^T〗_(intr.))，才導致我們所觀察到的 〖k_q^S〗_(obs.) 和 〖k_q^T〗_(obs.)的差異在不同狀態下的不同。在沒有溶劑籠效應 (solvent cage effect) 的情況下，〖k_q^T〗_(obs.)在固態環境極易受到形成電荷轉移複合體的能量的影響，相反的 〖k_q^S〗_(obs.)則維持受限於擴散常數控制，以致 〖k_q^S〗_(obs.) 和 〖k_q^T〗_(obs.)在固態下的差異比在溶液中還要明顯。這樣的差異使我們能在固態下觀察到螢光被氧氣焠滅的現象，未來可望能應用在使用有機螢光染料分子作為氧氣檢測器。

In this study, we aim for probing the emission quenched by O2 in solid phase. Special focus is on the O2 dependent fluorescence of a series of organic D-π-A phosphonium compounds adsorbed on the silica gel. The results show that the O2 quenching rate constant 〖k_q^S〗_(obs.)for fluorescence of 1-3 on the silica gel is in the order of 1010 M-1s-1, which are nearly on the same order as those measured for 1-3 and common reported organic compounds in solution. In yet another approach, the study of O2 quenching phosphorescence in solid phase renders O2 quenching rate constant for the triplet state, i.e., 〖k_q^T〗_(obs.), to be smaller than 〖k_q^S〗_(obs.) by two orders of the magnitude in general. Detailed investigation indicates that this stemmed from the intrinsic O2 quenching rate constants for singlet and triplet state subsequent to the formation of collisional complexes, i.e., 〖k_q^S〗_(intr.) and 〖k_q^T〗_(intr.) respectively, thus rendering the different behavior for 〖k_q^S〗_(obs.) and 〖k_q^T〗_(obs.) in different phases. In the absence of solvent cage effect, value of 〖k_q^T〗_(obs.) is greatly influenced by the formation energy of the O2-dye CT complex, whereas 〖k_q^S〗_(obs.) in solid phase is perceived to be nearly diffusion-controlled. The larger distinction between 〖k_q^S〗_(obs.) and 〖k_q^T〗_(obs.) in solid phase than that in solution makes O2 quenching fluorescence noticeable for dyes adsorbed on the silica gel, which thus leads to the feasible application of sensing O2 by regular fluorescence dyes adsorbed on porous solid substrates.