本論文以靜態光譜、超快時間解析螢光光譜(TRFL)及超快瞬態吸收光譜(TA)技術研究不同激發波長下4-硝基聯苯(4-nitrobiphenyl, 4-NBP)及2-硝基芴(2-nitrofluorene, 2-NF)在cyclohexane (CHX)及acetonitrile (ACN)溶劑中的激發態緩解動力學，並藉由理論計算的結果來輔助解釋4-NBP及2-NF在激發態的緩解機制。在以短波長(310 nm/320 nm)及360 nm飛秒脈衝雷射激發4-NBP及2-NF在CHX及ACN溶劑的TA光譜中，我們皆觀察到初始單重激發態之 ESA訊號具有極短的initial decay (τ1 < 100 fs)。特別重要的是在4-NBP於CHX溶劑中，因為其S2(ππ*)及S1(nπ*)態之間的能量差較大，使我們能夠在4-NBP於CHX溶劑中使用310 nm或360 nm脈衝雷射分別激發到S2(ππ*)或S1(nπ*)，進而發現其分別展現出波長範圍較窄的吸收峰或broad band的ESA譜帶。我們發現當使用310 nm或320 nm激發4-NBP/2-NF至S2(ππ*)態時，在TA光譜中缺乏可被觀測到的S1(nπ*)特徵譜帶，這暗示S2(ππ*)態的主要衰減途徑是直接ISC到三重態，而S2(ππ*)態IC至S1(nπ*)態過程相對很慢，無法與S2(ππ*)態ISC至三重態形成有效競爭。而從receiver triplet states進行IC至T1態的過程，其時間常數τ2a約1~2 ps。T1態進行VR的過程，其時間常數τ3約10 ps。最後，從T1態回到基態的過程，其時間常數τ4隨溶劑極性降低有變短的趨勢(τ4從ACN中> 50 ns到CHX中~ 2 ns)。在以310 nm/320 nm及350 nm/360 nm飛秒脈衝雷射激發的4-NBP及2-NF在CHX及ACN溶劑的TRFL光譜中，我們都觀察到極短的螢光衰減訊號且其皆呈現biexponential decay (τ1< 100 fs與τ2f約0.4~2 ps)。τ1主要為單重激發態同時進行超快ISC及VR的過程，而τ2f (0.4~2 ps)為S2(ππ*)態或是S1(nπ*)態在VR過程中在較低振動能階進行較慢之ISC至三重態的過程，與TA光譜中所觀測的τ2a並不相同，且僅佔很小的比例。

In this study, the excited-state relaxation dynamics of 4-nitrobiphenyl (4-NBP) and 2-nitrofluorene (2-NF) were investigated by steady-state spectroscopy, ultrafast time-resolved fluorescence (TRFL), and ultrafast transient absorption (TA) spectroscopy at various excitation wavelengths in cyclohexane (CHX) and acetonitrile (ACN) solvents. With the aid of theoretical calculations, we proposed an excited-state relaxation mechanism of 4-NBP and 2-NF. The TA spectra revealed a rapid initial decay of the singlet excited state (τ1 < 100 fs) for both molecules when excited at 310 nm/320 nm and 360 nm. Notably, for 4-NBP in CHX, there was a significant energy gap between the S2(ππ*) and S1(nπ*) states, enabling selective excitation of the two states and leading to the observation of and characteristic narrow/broad ESA bands. This study also found that the primary decay pathway for the S2(ππ*) state was direct intersystem crossing (ISC) to triplet states, with the internal conversion (IC) to S1(nπ*) being comparatively slow and inefficient. Additionally, the subsequent relaxation in the triplet states was characterized by time constants τ2a (1-2 ps) for IC to the T1 state and τ3 (~ 10 ps) for vibrational relaxation (VR). Finally, the process of returning from the T1 state to the ground state showed a trend of decreased time constants with reduced solvent polarity, with τ4 ranging from over 50 ns in acetonitrile to approximately 2 ns in cyclohexane. In TRFL spectra, biexponential decay patterns were observed with τ1 < 100 fs and τ2f ~ 0.4-2 ps. τ1 primarily represented the ultrafast simultaneous processes of ISC and VR within the singlet excited state. τ2f (0.4–2 ps) represented a slower ISC to the triplet state during VR at lower vibrational levels of the S2(ππ*) or S1(nπ*) states. The τ2f process was different from the τ2a observed in TA spectra and constituted only a small proportion of the observed fluorescence.

摘要 i
Abstract ii
誌謝 iii
目錄 iv
第一章 緒論 1
1.1 前言 1
1.2 NPAHs化合物激發態動力學之影響 2
1.3 本論文研究目的 8
第二章 實驗系統與技術 10
2.1 超快飛秒雷射系統 10
2.1.1 飛秒雷射產生源 11
2.1.2 能量再生放大器 15
2.1.3 波長調變器: TOPAS 20
2.2 超快時間解析螢光光譜 23
2.2.1 克爾光閘原理 23
2.2.2 超快時間解析螢光光譜系統架設 25
2.2.3 超快時間解析螢光光譜自動化數據擷取系統 34
2.2.4 儀器響應函數 36
2.2.5 超快時間解析螢光光譜之時間延遲校正與靈敏度校正 40
2.2.6 扣除Raman訊號 51
2.3 超快瞬態吸收光譜 52
2.3.1 超快瞬態吸收光譜原理 52
2.3.2 瞬態吸收光譜系統之光路架設 54
2.3.3 瞬態吸收光譜自動化數據擷取系統 58
2.3.4 儀器響應函數 60
2.3.5 瞬態吸收光譜時間延遲校正 61
2.3.6 超快瞬態吸收光譜背景訊號扣除 63
2.4 實驗藥品配置 67
第三章 實驗結果與討論 68
3.1 靜態吸收光譜 68
3.2 靜態放光光譜 70
3.3 超快時間解析螢光光譜 72
3.3.1 4-NBP之TRFL光譜 73
3.3.2 2-NF之TRFL光譜 81
3.4 超快瞬態吸收光譜 89
3.4.1 4-NBP之TA光譜 90
3.4.2 2-NF之TA光譜 108
第四章 理論計算與綜合討論 126
4.1 DFT理論計算 126
4.1.1 4-NBP及2-NF在S0、S1及S2態最佳化構型之理論計算 126
4.1.2 4-NBP及2-NF於CHX在S1及S2態最佳化構型各能態之垂直激發能量計算 137
4.2 綜合討論 142
第五章 結論 148
參考文獻 150

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