利用飛秒瞬態吸收光譜技術研究鍵結於金奈米粒子表面上的2-苯硫醇基,5-苯基,3-丁基呋喃之光學特性及三核鎳系、鈷系與鉻系金屬串錯合物之電子激發態動態學

Optical Properties of 2-Benzylthiol, 5-benzyl, 3-butylfuran Interacting with Gold Nanoparticles and Dynamic of Electronically Excited States of Ni3, Co3, and Cr3 Metal Complexes Studied by Femtosecond Transient Absorption Spectroscopy

鄭照翰(Chao-Han Cheng)

指導教授 ： 陳益佳

國立清華大學/理學院/化學系/博士(2008年)

https://doi.org/10.6843/NTHU.2008.00111

摘要

我們利用飛秒瞬態吸收光譜技術，研究2-苯硫醇基,5-苯基,3-丁基砆喃（3SAH）、5 nm金奈米粒子（GNP），以及粒徑2、5、7與10 nm的3SAH-GNP系統之電子激態動態反應。對於3SAH，其濃度大於1×10-6 M時會產生堆疊體。由於分子堆疊後造成振動鬆弛等非放光機制遲緩，使放光生命期1 ns長於單體的0.2 ns。而5 nm GNP，利用雙溫度模型可擬合出電子-聲子與聲子-聲子交互作用之時間常數2.3與140 ps。而非均相性瞬態吸收實驗，可得到＜60 fs之去相位化時間，說明熱電子之間的散射速率相當快。對於3SAH-GNP，3SAH+的生成時間（＜200 fs）說明，3SAH激態電子轉移至GNP的機制具有高效率。並且當粒徑變小時，表面體積比增加，GNP會電子轉移回復至3SAH*；此機制與電子-聲子交互作用競爭，使GNP熱釋解的過程加快。此外，我們亦利用瞬態吸收光譜技術研究三核金屬串錯合物Ni3(dpa)4(NCS)2、Ni3(dpa)4Cl2、Co3(dpa)4(NCS)2與Cr3(dpa)4Cl2之激態動態變化。配位基中心之π-π*與電荷轉移能態均快速地轉移至配位基場能態，時間常數分別為0.2-0.3（Ni3）、＜0.1（Co3）與 ＜0.1 ps（Cr3）。此外，配位基場能態回到基態之時間常數，與自旋度-軌域耦合常數以及最低能量激發態與基態間的能量差有關，分別為3（Ni3）、15（Co3）與200 ps（Cr3）。

關鍵字

超快 ； 奈米金 ； 電子轉移 ； 金屬串錯合物 ； 激發態動態學

並列摘要

Dye molecule 3SAH, gold nanoparticle (GNP), and 3SAH-GNP were measured by sub-picosecond transient absorption spectroscopy. The aggregation of 3SAH exists with concentrations larger than 1×10-6 M, and shows long emission lifetime due to more rigid structure. For 5 nm GNP, time constants of electron-phonon and phonon-phonon are obtained to be 2.3 and 140 ps, respectively in fitting to a two-temperature model. The dephasing time less than 60 fs indicates an ultrafast electron scattering. For 3SAH-GNP, the absorption of 3SAH+ arises less than 200 fs indicating the electron injection from excited 3SAH to GNP with high efficiency. The process of back electron transfer from GNP to 3SAH competes well with electron-phonon interaction in GNP, and becomes dominant under condition of large ratio of surface to volume in GNP. The participation of back electron transfer plays a second pathway for heat dissipation in GNP. Trinucleus metal complexes, Ni3(dpa)4(NCS)2, Ni3(dpa)4Cl2, Co3(dpa)4(NCS)2,and Cr3(dpa)4Cl2 are studied by transient absorption spectroscopy. Their ligand-center π-π* and charge transfer states are accessed via laser excitation then quickly transfer to ligand-field states at time constants 0.2-0.4 (Ni3), <0.1 (Co3), and <0.1 ps (Cr3), respectively. Time constants obtained for ligand-field states back to ground state are related to the spin-orbit coupling constants (Ni3 > Co3 > Cr3) and the energy gap between lowest-lying excited state and ground state (Cr3 > Co3 ≈ Ni3). They are obtained to be 3 (Ni3), 15 (Co3), and 200 ps (Cr3).

並列關鍵字

ultrafast ； gold nanoparticle ； electron transfer ； metal string ； excited-state dynamics

參考文獻

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