利用螢光上轉換光譜技術研究光收成共聚物之能量轉移過程

劉冠麟(Kuan-Lin Liu)

指導教授 ： 陳益佳

國立清華大學/理學院/化學系/博士(2009年)

摘要

我們利用螢光上轉換技術，研究一系列以矽烷基 (SiMe2) 作為間隙物且具有立體規則性 (regioregular) 之光收成共聚物 (D1,3A)m，其中給體D與受體A分別為4,4-divinylbiphenyl以及4,4-divinylstilbene。由於單一矽烷基與π-系統沒有電子共軛，可以視為絕緣間隙物，聚合物的光物理性質會類似於其相對應的單體，而烷基則可以增加聚合物在有機溶劑中的溶解度。以266 nm光源激發，給體單體之螢光訊號在最初有一個迅速的 (~0.1 ps) 上升成分 (τ1)，接著以雙自然指數衰減，其時間常數分別為數十個與數百個皮秒 (τ2,3)，τ1指派為Sn→S1的內轉換而τ2,3則是分別為構型緩解 (平面化) 以及S1激發態的生命期，其中τ2與溶劑的粘度呈現出線性關係，證實在S1激發態構型緩解為主要的緩解途徑。當激發 (D1,3A)m內部的給體部分，給體受體之能量傳遞皆相當有效，飛秒時間解析螢光指出 (D3A)m與 (DA)m中能量傳遞的速率分別為 (0.3 ps)-1以及 (0.6 ps)-1。(D3A)m中所觀察到的能量傳遞速率可由Frster理論良好地預測，顯示能量傳遞主要是透過偶極–偶極作用力。然而 (D3A)m與 (DA)m中能量傳遞速率的差異，則暗示兩種共聚物內部的給體–受體之間具有不同的偶合作用力。最後，由於共聚物主鍊容易摺疊，(D3A)m與 (DA)m內部皆包含分子內聚集體，其能量淬息速率分別約為 (5 ps)-1與 (7 ps)-1。本實驗結果顯示以矽烷基為間隙物的小分子或是共聚物，由於合成相當簡易與迅速的能量傳遞速率，在光收成材料之應用方面具有很好的發展潛力。

關鍵字

能量傳遞

並列摘要

We used fluorescence up-conversion technique to investigate a series of regioregular silylene-spaced alternating donor-acceptor copolymer (D1,3A)m. Here D and A denote 4,4-divinylbiphenyl and 4,4-divinylstilbene, respectively. Silylene group can prevent over-extended conjugation between the chromophores in the polymer so that the photophysical properties of the polymer can be tuned. The alkyl substituents on silicon render the polymer more soluble in organic solvents. With 266 nm excitation the fluorescence curves of donor monomer exhibit a rise time constant 100 fs, and two decay time constants, 7-65 ps and 1 ns. We attribute the former rise to internal conversion from Sn to the S1 state, and the latter decay to geometric relaxation and the lifetime of the S1 state. Only the tens of picosecond decay shows a dependence on the solvent viscosity, indicating that the torsional motion dominates the relaxation. Upon excitation of donor moieties in (D3A)m, the fluorescence is almost exclusively from the acceptor regardless of the excitation wavelength, indicating an efficient energy transfer between donor and acceptor. Femtosecond time-resolved fluorescence indicates a rate (0.3 ps)-1 and (0.6 ps)-1 for energy transfer between S1 states of the donor and the acceptor is observed in (D3A)m and (DA)m, respectively. The observed energy transfer rate in (D3A)m is well described by the Frster theory, indicating that dipole–dipole interaction dominates the energy transfer process. The discrepancy between the energy transfer rates observed in (D3A)m and (DA)m implies the coupling between donor and acceptor is different. Finally, intramolecular aggregation is observed in both (D3A)m and (DA)m, with rates (5 ps)-1 and (7 ps)-1 respectively, of energy transfer to the aggregates. The experimental results show that silylene-spaced copolymers are promising in the application of light-harvesting materials from the ease of preparation and the ultrarapid rate of energy transfer.

並列關鍵字

energy transfer

參考文獻

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