冒牌自然老師

Speaker: 許昭萍 教授 Prof. Chao-Ping (Cherri) Hsu (中央研究院化學所 Institute of Chemistry, Academia Sinica)
Title: Electronic couplings for electron transfer and excitation energy transfer
Time: 14:20, Apr. 14(Wed.), 2010
Place: R833, New Physics Building, National Taiwan University

相關論文
Hsu, C.-P. The Electronic Couplings in Electron Transfer and Excitation Energy Transfer. Acc. Chem. Res. 2009, 42, 509.原文論文

代表作名稱：
1. Lin, B. C., Cheng, C. P.*, You, Z.-Q., Hsu, C.-P.*, "Charge Transport Properties of
Tris(8-hydroxyquinolinato)aluminum(III): Why It Is an Electron Transporter", J. Am.
Chem. Soc.(2005), volume 127, pp. 66-67
2. Chen, H.-C. , You, Z.-Q., Hsu, C.-P.*, "The mediated excitation energy transfer: Effects
of bridge polarizability", J. Chem. Phys.(2008), Volume 129, 084708
3. You Z.-Q., Hsu C.-P., Fleming G.-R., "Triplet-triplet energy-transfer coupling: Theory and
calculation", J. Chem. Phys. (also selected for the Feb. 6, 2006 issue of Virtual Journal of
Nanoscale Science & Technology.)(2006), volume 124, 044506

許昭萍副研究員在量子化學計算中使用difference density 直接得到分子間或分子內之電子耦合值，對困難的電子耦合問題提出一重要且非常聰明之解決方法。此方法經仔細測試證明確實有效，可應用在任何donor-acceptor 之系統，使我們對能量轉移的瞭解邁出一大步，因此在學術上具有突破和貢獻。許博士所提出的三篇論文，均可堪稱為在電子轉移和能量轉移領域中 “state-of-art＂之作。兩篇JCP 的論文中，一篇詳細描述如何處理並解決在三重態能量轉移上所遇到之困難問題，顯示作者能充分駕馭其專業的能力。她的解決方法雖然在觀念上很簡單，但在這之前卻無人曾想到。不難預料，此方法將對量子化學造成很大的衝擊，甚至將在日後成為一種標準的計算方式。另一篇JCP 論文探討橋接分子在能量轉移中所扮演的角色，首度提出橋接分子的極化率（polarizability） 才是對能量轉移發生影響的主因，比傳統上以能階差來解釋更加直觀且易於應用。第三篇JACS的論文則是應用在了解並推測OLED 常用分子Tris(8-hydroxyquinolinato)aluminum(III) 之電荷傳輸特性中電子轉移遠快於電洞轉移之原因。


演講者簡介
許昭萍
    * 79年台灣大學化學系學士，
    * 81年台灣大學化學研究所碩士，
    * 86年美國加州理工學院化學博士，
    * 87至90年美國加州大學柏克萊分校米勒研究員，
    * 91至96年中央研究院化學研究所助研究員。
    * 96年迄今中央研究院化學研究所副研究員。
    * 91年美國李氏傳統基金會獎助金。
    * 97年度吳大猷先生紀念獎。
    * 98年度中央研究院年輕學者研究著作獎。

實驗室網頁

Biography

Chao-Ping Hsu was born in Taiwan in 1968. She received a Ph.D. in Chemistry in 1998 from the California Institute of Technology. She was a Miller Research Fellow at the University of California at Berkeley from 1998 to 2001. She joined the Institute of Chemistry, Academia Sinica, in 2002, where she is now an associate research fellow. Her main research interest in computational chemistry has been in the characterization of electronic coupling for charge and energy transports.


研究領域：

    先進材料中的電荷傳輸、能量轉移性質探討

    近年來由於先進材料發展及對生物分子的深入研究，電子轉移反應的重要性日益顯著。電子轉移過程在許多化學反應中扮演了不可或缺的角色。隨著電子轉移，反應物的價數改變，伴隨著能量的移轉或是化學鍵的變化，如氧化還原反應、電化學反應及光誘導電荷分離反應等。自1950年代以來，許多的實驗跟理論研究探討電子轉移的反應機制以及控制電子轉移速率的各種因素。近年來許多研究探討有機小分子應用於分子電路 (molecular electronics) 的概念和模型，開啟了電子轉移應用在奈米尺度 (Nano-scale) 的分子電路元件設計的研究。其中以電子予體 (donor) - 鍵橋 (bridge) - 電子受體 (acceptor)（簡稱為DBA）的設計在近代的研究中扮演了重要的地位。利用DBA分子之設計可以了解奈米級分子導線(molecular wire) 、分子整流器 (unimolecular rectifiers) 的特性及應用，人造分子機械 (artificial molecular machine ) 以及利用分子內電荷轉移的有無作為分子邏輯開關的基礎設計，除此之外，有機發光二極體 (organic light-emitting diodes) 內的電子電洞的傳輸與結合的過程，延長電荷轉移後產生的離子對的生命期以提高太陽能電池的轉換效率。在生物體系裡，電子轉移也是一項重要的反應，例如光合作用中反應中心的電子傳遞及其他各個層面，電子轉移反應都參與其中。

    在常見的，屬於弱耦合的電子轉移反應中，電子轉移耦合值的大小往往會影響及決定其反應速率，因此，用理論計算的方法估計電子轉移耦合值，不但能提供一深入了解實驗結果的途徑，而且也可提供功能性分子設計的重要依據。

    我們在有關電子轉移的耦合值的計算，提出了新的方法，並且將這些方法應用在具功能性的有機分子上。除了電子轉移之外，分子激發的能量轉移也是我們關心的重點。能量轉移包括了單重態－單重態間的，以 Forster 偶極距作用為代表的情況，也包括了三重態－三重態間的轉移，其作用的機制類似於 Dexter 交換耦合。我們最近首度提供了全初始的三重態能量交換的耦合值計算，而且也首度能跟實驗值對照。

    生物系統的動態模擬

    利用我們在計算化學上的認識與經驗，我們開發了系統分子生物學方面，有關分子的動態反應的描述和計算的工具。透過與實驗學家們合作，我們提供數學和電腦模擬的結果，能夠加深對生物體系的了解。





The transport of charge via electrons and the transport of excitation energy via excitons are two processes of fundamental importance in diverse areas of research. Characterization of electron transfer (ET) and excitation energy transfer (EET) rates are essential for a full understanding of, for instance, biological systems (such as respiration and photosynthesis) and opto-electronic devices (which interconvert electric and light energy). In this Account, we examine one of the parameters, the electronic coupling factor, for which reliable values are critical in determining transfer rates. Although ET and EET are different processes, many strategies for calculating the couplings share common themes. We emphasize the similarities in basic assumptions between the computational methods for the ET and EET couplings, examine the differences, and summarize the properties, advantages, and limits of the different computational methods.

The electronic coupling factor is an off-diagonal Hamiltonian matrix element between the initial and final diabatic states in the transport processes. ET coupling is essentially the interaction of the two molecular orbitals (MOs) where the electron occupancy is changed. Singlet excitation energy transfer (SEET), however, contains a Frster dipole−dipole coupling as its most important constituent. Triplet excitation energy transfer (TEET) involves an exchange of two electrons of different spin and energy; thus, it is like an overlap interaction of two pairs of MOs. Strategies for calculating ET and EET couplings can be classified as (1) energy-gap-based approaches, (2) direct calculation of the off-diagonal matrix elements, or (3) use of an additional operator to describe the extent of charge or excitation localization and to calculate the coupling value.

Some of the difficulties in calculating the couplings were recently resolved. Methods were developed to remove the nondynamical correlation problem from the highly precise coupled cluster models for ET coupling. It is now possible to obtain reliable ET couplings from entry-level excited-state Hamiltonians. A scheme to calculate the EET coupling in a general class of systems, regardless of the contributing terms, was also developed.

In the past, empirically derived parameters were heavily invoked in model description of charge and excitation energy drifts in a solid-state device. Recent advances, including the methods described in this Account, permit the first-principle quantum mechanical characterization of one class of the parameters in such descriptions, enhancing the predictive power and allowing a deeper understanding of the systems involved.