本論文透過實驗室自行架設之超快時間解析螢光(time-resolved fluorescence, TRFL)光譜儀與超快瞬態吸收(transient absorption, TA)光譜儀，探討4-甲氧基-4'-硝基聯苯(4-methoxy-4'-nitrobiphenyl, MONBP)與2-甲氧基-7-硝基芴(2-methoxy-7-nitrofluorene, MONF)於cyclohexane (CHX)與acetonitrile (ACN)中之激發態動力學行為，並輔以time-dependent density functional theory (TD-DFT)理論計算解析其緩解機制。靜態吸收光譜與理論分析顯示，兩分子於短波長激發下主要進入1(ππ*)態，但於CHX中亦可觀察到微弱的1(nπ*)態之特徵，顯示少部分分子可能直接被激發至1(nπ*)態。TA與TRFL光譜結果指出，在CHX中兩分子具有快速的激發態緩解過程，自1(ππ*)及少量的1(nπ*)態經由intersystem crossing (ISC)進入三重態，並進一步緩解至最低三重態後回到基態，顯示非極性環境有利於三重態生成。而在ACN中，兩分子之激發態壽命明顯延長，顯示溶劑極性對激發態具有穩定作用。初期TA光譜中可同時觀察1(nπ*)與1(ππ*)態特徵峰，推測部分1(ππ*)態可經由超快internal conversion (IC)到1(nπ*)態後再進行ISC。理論計算亦顯示於高極性環境中1(ππ*)態能量下降，且其穩定構型附近缺乏密集三重態，降低直接進行ISC之可能性。綜合實驗與理論結果，我們建立MONBP與MONF在CHX與ACN中之激發態緩解模型，以說明其在不同溶劑環境下之激發態緩解動力學。

In this study, we employed a home-built femtosecond time-resolved fluorescence (TRFL) spectrometer and transient absorption (TA) spectrometer to investigate the excited-state dynamics of two nitroaromatic compounds, 4-methoxy-4’-nitrobiphenyl (MONBP) and 2-methoxy-7-nitrofluorene (MONF), in cyclohexane (CHX) and acetonitrile (ACN). Time-dependent density functional theory (TD-DFT) calculations were also performed to support the interpretation of their excited-state relaxation mechanisms. Steady-state absorption spectra and theoretical analysis revealed that both molecules are primarily excited to the 1(ππ*) state upon near UV excitation, though a minor contribution from direct excitation to the 1(nπ*) state was also observed in CHX. TA and TRFL results indicated that the initial 1(ππ*) and 1(nπ*) states in CHX undergo ultrafast intersystem crossing (ISC) to triplet states and eventually relax to the ground state, suggesting that the nonpolar environment favors efficient triplet formation. In contrast, significantly prolonged excited-state lifetimes were observed in ACN, highlighting the stabilizing effect of polar solvents. Early-time TA spectra revealed characteristic absorption features of both 1(ππ*) and 1(nπ*) states, suggesting that a portion of the population undergoes ultrafast internal conversion (IC) from the 1(ππ*) to the 1(nπ*) state before ISC. TD-DFT calculations further showed that in polar solvents, the 1(ππ*) state is energetically lowered and lacks nearby triplet states around its relaxed geometry, which may hinder direct ISC. Combining experimental data with theoretical analysis, we propose a relaxation model to describe the excited-state dynamics of MONBP and MONF in different solvent environments.