以 Fragment Charge Difference 及 Generalized Mulliken-Hush 方法執行電子轉移耦合之全初始計算: 應用於在光激發及振動影響下之剛性鍵橋連接之電子予體-受體分子系統

李昇叡(Sheng-Jui Lee)

指導教授 ： 陳益佳 ； 許昭萍

國立清華大學/理學院/化學系/博士(2010年)

摘要

我們使用fragment charge difference (FCD) [A. A. Voityuk and N. J. Rösch, Chem. Phys. 117, 5607 (2002)] 及 generalized Mulliken-Hush (GMH) [R. J. Cave and M. D. Newton, Chem. Phys. Lett. 249, 15 (1996), R. J. Cave and M. D. Newton, J. Chem. Phys. 106, 9213 (1997)] 等方法進行光激發電子轉移中電子耦合值之計算。我們測試了以不同芳香環作為電子予體之分子，並且發現予體片段之兩局部激發態具有不同之對稱性，導致截然不同之電子轉移速率。經由對稱性之判斷，我們發現在電子耦合值極小之情況下，GMH方法較FCD方法存在著問題。在一些情況下，電荷轉移之變遷組成存在於兩局部激發態中。此時，我們可以用三態模型 (3-state model) 來處裡GMH方法 [M. Rust, J. Lappe, and R. J. Cave, J. Phys. Chem. A 106, 3930 (2002)]，並且可用於FCD方法。簡單的矩陣對角化亦可解決此一問題，其結果並與三態模型來比較。最後，電子轉移速率可被計算並與實驗結果作比較。我們亦利用Medvedev及Stuchebrukhov之式子 [E. S. Medvedev and A. A. Stuchebrukhov, J. Chem. Phys. 107, 3821 (1997)] 進行多環橋鍵結之分子在振動模式影響下之電子轉移速率計算。振動模式之影響解釋了在對稱性不允許的情況下，電子轉移過程仍可發生的可能性。我們估算出經由振動影響之平均耦合值，與實驗結果相當。

關鍵字

光誘發電子轉移 ； generalized Mulliken-Hush 方法 ； fragment charge difference 方法 ； 多態模型 ； 對稱性 ； 振動耦合

並列摘要

The electronic coupling values for photo-induced electron transfer (ET) were calculated by the fragment charge difference (FCD) [A. A. Voityuk and N. J. Rösch, Chem. Phys. 117, 5607 (2002)] and the generalized Mulliken-Hush (GMH) schemes [R. J. Cave and M. D. Newton, Chem. Phys. Lett. 249, 15 (1996), R. J. Cave and M. D. Newton, J. Chem. Phys. 106, 9213 (1997)]. We tested several molecules with several different aromatic donors and acceptor combinations, and found that the lowest two local excited (LE) states of each molecule are very different in their ET rates due to their symmetries. We found that the FCD is less prone to problems commonly seen in the GMH scheme especially when the coupling values are small. For a 3-state case where the charge transfer (CT) state is coupled with two different locally excited (LE) states, we propose to follow the 3-state approach for the GMH scheme [M. Rust, J. Lappe, and R. J. Cave, J. Phys. Chem. A 106, 3930 (2002)], and found that it works well with the FCD scheme. A simplified direct diagonalization based on the Rust’s 3-state scheme was also proposed and tested. The overall electron transfer (ET) coupling rates were also calculated and compared to experimental results. We also used several rigid, polycyclic DBA molecules to test for the vibronic effect on the electronic coupling of a rigid donor-bridge-acceptor molecule by Medvedev and Stuchebrukhov’s expression [E. S. Medvedev and A. A. Stuchebrukhov, J. Chem. Phys. 107, 3821 (1997)]. The vibronic effect offers an averaged ET coupling value that is consistent to the observed ET rate in the symmetry forbidden case.

並列關鍵字

Photoinduced electron transfer ； generalized Mulliken-Hush ； fragment charge difference ； multi-state model ； symmetry ； vibronic coupling

參考文獻

1. Introduction

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