共價鍵連接多並苯二聚體系統中單重態分裂之CISD-EOM理論計算研究

A CISD-EOM Study of Singlet Fission in Covalently-linked Oligoacene Dimers

黃俊銓(Chun-Chuan Huang)

指導教授 ： 鄭原忠

國立臺灣大學/理學院/化學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202201953

摘要

單重態分裂是一種由一個單重態電子激發態分裂成兩個三重態激發的過程，由於其顯著提高太陽能電池效率的潛力而引起了廣泛的研究關注。在這項工作中，我們提出於組態交互作用框架中利用分塊對角化過程，來構建適合描述分子二聚體中單重態分裂過程的近似電子非絕熱狀態。我們的方法明確地描述了分子二聚體系統單重態分裂所涉及的激發態特徵。我們首先研究三個滑移堆疊結構的聚苯二聚體：蔥、並四苯和並五苯。在確認理論預測符合實驗觀察結果後，我們進一步透過我們的方法來研究共價鍵連接的聚並苯二聚體之間的差異。我們得出結論：高效率的單重態分裂主要取決於單重態能量高於兩個三重態的總能量，而不是單重態和三重態之間有強耦合。然而，當兩個態能量差異在不同分子間較小時，耦合將是影響單重態分裂效率的主要因素。此外，我們系統性地闡明了以共價鍵連接的聚苯二聚體中橋接分子的作用，並更進一步分析透過鍵或是透過空間耦合的比較。通過比較具有不同苯基連接位置的二聚體，我們在 6,13-雙（三異丙基甲矽烷基乙炔基）並五苯和雙（5-乙炔基並四苯）苯系列中，觀察到的兩者具有不同偏好位置的原因為兩者不同的分子尺寸。此外，我們檢查了 連接分子的π共軛對於分子內 SF 是否重要。我們發現連接分子的π共軛提供了大量的透過鍵耦合，因此顯著提高了單重態分裂效率。最後，我們使用 CISD-EOM 方法計算的超交換有效耦合與實驗觀測到的單重態分裂速率高度相關。我們提供了一個全面的理論視角來理解共價鍵連接的聚並苯系統中的單重態分裂過程。

關鍵字

交替烴 ； 多並苯 ； 分子設計 ； 單重態分裂 ； 組態交互作用

並列摘要

Singlet fission has attracted intensive research attention because of its potential to significantly improve efficiency of solar cells. In this work, we propose to utilize an intermediate block-diagonalization procedure in the configuration interaction framework to construct approximate electronic diabatic states suitable for modeling singlet fission process in molecular dimers. Our procedure unambiguously interprets the characters of the excited states involved in the singlet fission of a molecular dimer system. We first examine our method on three slip-stacked oligoacene dimers, anthracene, tetracene and pentacene. After showing agreements with experimental observation, we further apply our method to investigate singlet fission in the covalently-linked dimers. We conclude that the energetic requirement has the higher priority over the coupling requirement. However, once the energy barrier is small enough compared to the couplings, the coupling will be the main factor which affects the SF time scale. Furthermore, we systematically elucidate the role of linker in covalently-linker oligoacene dimers, and focus on a comparison based on the through-bond and through-space separation of the SF couplings. By comparing SF couplings of dimers with different phenyl linking positions, we explain the different preferred position observed in TIPSP and BETB series. Furthermore, we examine whether or not a $\pi$-conjugated linker is essential for intramolecular SF. Our calculation indicated that the conjugation provides a significant amount of through-bond coupling, therefore significantly enhance the SF efficiency. Finally, the superexchange effective couplings calculated using CISD-EOM method are shown to exhibit high correlation with experimental SF rates. We provide a comprehensive theoretical perspective to understand the SF process in covalently-linked oligoacene systems.

並列關鍵字

alternant hydrocarbons ； polyacenes ； molecular design ； singlet fission ； configuration interaction

參考文獻

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