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姓名 孫慧倫(Hui-lun Sun) 查詢紙本館藏 畢業系所 化學學系 論文名稱 利用時間相關的密度泛涵理論研究HBI分子及其衍生物在第一激發態的位能曲線
(The Potential Energy Surface of the First-Excited State of HBI and its Derivatives: A TD-DFT Study)相關論文 檔案 [Endnote RIS 格式] [Bibtex 格式] [相關文章] [文章引用] [完整記錄] [館藏目錄] 至系統瀏覽論文 ( 永不開放) 摘要(中) 本篇利用時間相關的密度泛涵理論(TD-DFT)對 2-(2’-hydroxyphenyl)benzimidazole (HBI) 以及其胺基取代衍生物, HBI-NH2 和 HBI-NEt2 ,在激發態時的位能曲面進行探討。HBI分子受到光的激發之後,在激發態時會進行分子內質子轉移的行為 (ESIPT),而形成釋放螢光的異構化結構,以S1-Tsyn簡稱之。然而當HBI分子在苯酚的對位 (para) 上接上胺基取代基後,其螢光的表現和螢光量產率與HBI分子相比卻有著明顯的不同。因此我們希望能藉由激發態位能曲線圖的計算,瞭解HBI系列分子在激發態的分子行為。
根據計算結果,在激發態HBI分子進行ESIPT時,是為不具有活化能 (activation energy) 的反應。而與HBI分子不同的是,其胺基取代衍生物,HBI-NH2 和HBI-NEt2,則具有反應活化能。此活化能的存在降低釋放螢光物種的生成,使得HBI-NEt2 的螢光量子產率較HBI分子低。另外,HBI 、HBI-NH2 、HBI-NEt2三個分子在激發態時,亦可能存在穩定而非平面的分子結構,且在C1的位置上具有角錐化 (pyramidalization)。因此,我們以扭轉N6-C1-C2-C3的二面角與在C1位置上的角錐化程度作為反應座標,進行二維位能曲線圖的計算,並分析其可能的最低能量路徑,探討此三個分子於激發態的行為。反應活化能的存在,可說明實驗上所觀測到與溫度相關之螢光量子產率的變化。當溫度升高,S1-Tsyn的比率隨之降低,S1-TCT(非輻射鬆弛)的比例則相對提高,螢光量子產率也隨之下降。但三個分子間,較為特別的是HBI分子在乙醇溶劑下,其S1-TCT能量較S1-tau高,因此當溫度升高時,逆反應的速度也隨之提高,而使得HBI分子在乙醇溶劑下,其螢光量子產率和溫度無關。
摘要(英) The potential energy surfaces (PES) of the first singlet excited state (S1) of 2-(2’-hydroxyphenyl)benzimidazole (HBI) and its amino substituted derivatives (HBI-NH2 and HBI-NEt2) are investigated using time-dependent density functional theory. Upon excitation, these molecules undergo the excited-state intra-molecular proton transfer process (ESIPT) to produce their excited tautomeric forms, the major species of fluorescence. Interestingly, when HBI is substituted by a diethyl amino group at para-position of phenyl group, the fluorescence quantum yield is significant reduced. We investigate the possible quenching mechanisms by searching the excited state PES connecting with the fluorescing tautomeric form.
We found that the ESIPT is energy barrier-less for HBI; however, there is a low energy barrier (e.g. Ea = 1.98 kcal/mole for HBI-NEt2 in ethanol) exists retarding the fast ESIPT of HBI-NH2 and HBI-NEt2. This barrier first reduces the fluorescence quantum yield of HBI-NEt2 in relative to that of HBI. More interesting, these three molecules studied here also can adopt two stable charge-transfer forms in their S1 state. The S1-CT conformer has a non-planar structure; moreover, it is pyramidalized at benzimidazole.
The formation of S1-CT state can quench the fluorescence of excited tautomeric form. The energy barrier for S1-tautomer to S1-CT reaction is similar for these three molecules (ca. 2.5 kcal/mol). Moreover, the S1-CT forms for HBI-NH2 and HBI-NEt2 have lower energy than their corresponding tautomers. Therefore, increasing the temperature will speed up the formation of S1-CT conformer and further quench the fluorescence, consistent with experimental observations. Interesting, the S1-CT form of HBI is less stable than its tautomer. Increasing the temperature though speeds up the formation of CT conformer; however, it also enhances the reverse reaction resulting in a T-independent fluorescence quantum yield.
關鍵字(中) ★ 激發態
★ 位能曲線圖ㄝ
★ 時間密度泛涵理論關鍵字(英) ★ 2-(2'-hydroxyphenyl)benzimidazole
★ excited-state potential energy surface
★ TDDFT論文目次 Content
Content i
List of Figures ii
List of Tables iii
Chapter 1 Introduction 1
Chapter 2 Computational Methods 5
Chapter 3 Results and Discussion 7
3-1 Stationary Points at So and S1 States 7
3-2 Structure and Structural Change after Reaction 15
3-3 Mulliken Charge Population Analysis 31
3-4 Potential Energy Curve of ESIPT 35
3-5 Potential Energy Surface of Excited-State Charge Transfer 40
3-6 Effect of the Amino Group on ESIPT Process 45
3-7 Effect of the Amino Group on the Formation of S1-TCT state 47
Chapter 4 Summary 48
References 50
Appendix 53
List of Figures
Figure 1 A scheme shows the various structures of HBI coupling the ESIPT and CT processes. 4
Figure 2 Studied Molecular Systems and Atom Labels. 6
Figure 3.1 HOMO and LUMO orbitals of So-Nsyn (a and b) and So-Tsyn (c and d) forms calculated at PBE0/SVP level in the gas phase. 17
Figure 3.2 The structures of CT states of HBI in ethanol. 18
Figure 3.3 Potential energy curve of the HBI molecule as a function of O4…H5 distance (in Å). 37
Figure 3.4 Potential energy curve of the HBI-NH2 molecule as a function of O4…H5 distance (in Å). 38
Figure 3.5 Potential energy curve of the HBI-NEt2 molecule as a function of O4…H5 distance (in Å). 39
Figure 3.6 Potential energy surface of the S1 state of HBI molecule in ethanol as a function of N6-C1-C2-C3 torsion angle and pyramidalization angle at C1 atom. 42
Figure 3.7 Potential energy surface of the S1 state of HBI-NH2 molecule in ethanol as a function of N6-C1-C2-C3 torsion angle and pyramidalization angle at C1 atom. 43
Figure 3.8 Potential energy surface of the S1 state of HBI-NEt2 molecule in ethanol as a function of N6-C1-C2-C3 torsion angle and pyramidalization angle at C1 atom. 44
List of Tables
Table 3.1 Stationary energies of Nsyn, Tsyn and TCT forms of HBI at ground state (So) and first singlet excited state (S1) in ethanol.. 9
Table 3.2 Stationary energies of Nsyn, Tsyn and TCT forms of HBI at ground state (So) and first singlet excited state (S1) in cyclohexane.. 10
Table 3.3 Stationary energies of Nsyn, Tsyn and TCT forms of HBI-NH2 at ground state (So) and first singlet excited state (S1) in ethanol. 11
Table 3.4 Stationary energies of Nsyn, Tsyn and TCT forms of HBI-NH2 at ground state (So) and first singlet excited state (S1) in cyclohexane. 12
Table 3.5 Stationary energies of Nsyn, Tsyn and TCT forms of HBI-NEt2 at ground state (So) and first singlet excited state (S1) in ethanol. 13
Table 3.6 Stationary energies of Nsyn, Tsyn and TCT forms of HBI-NEt2 at ground state (So) and first singlet excited state (S1) in cyclohexane.. 14
Table 3.7 Selected geometric parameters of Nsyn, Tsyn and TCT forms of HBI in ethanol at So and S1 states. 19
Table 3.8 Selected geometric parameters of Nsyn, Tsyn and TCT forms of HBI in cyclohexane at So and S1 states. 21
Table 3.9 Selected geometric parameters of Nsyn, Tsyn and TCT forms of HBI-NH2 in ethanol at So and S1 states. 23
Table 3.10 Selected geometric parameters of Nsyn, Tsyn and TCT forms of HBI-NH2 in cyclohexane at So and S1 states. 25
Table 3.11 Selected geometric parameters of Nsyn, Tsyn and TCT forms of HBI-NEt2 in ethanol at So and S1 states.. 27
Table 3.12 Selected geometric parameters of Nsyn, Tsyn and TCT forms of HBI-NEt2 in cyxlohexane at So and S1 states. 29
Table 3.13 Mulliken charge population and dipole moment of various S1 states of HBI. 32
Table 3.14 Mulliken charge population and dipole moment of various S1 states of HBI-NH2. 33
Table 3.15 Mulliken charge population and dipole moment of various S1 states of HBI-NEt2 34
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指導教授 蔡惠旭(Hui-Hsu Gavin Tsai) 審核日期 2009-8-28 推文 facebook plurk twitter funp google live udn HD myshare reddit netvibes friend youpush delicious baidu 網路書籤 Google bookmarks del.icio.us hemidemi myshare