笏酮及咔唑衍生物在溶液中之光物理與光化學研究

Abstract

本論文主要分為兩大主題。第一主題在探討笏酮分子（9-Fluorenone，9F）及其衍生物1-羥基笏酮分子（1-Hydroxy-9-Fluorenone，1-HOF）在不同極性溶劑中的光譜與動力行為。第二主題為藉由量子化學計算來解釋在發藍光二極體中，可作為電洞傳輸層和發光層的咔唑衍生物2,7-DPVTCz及3,6-DPVTCz分子在螢光量子產率上極大差異的現象。在第一主題部份，我們利用時間相關單光子技術系統（Time-Correlated Single Photon Counting，TCSPC）來研究9F及其衍生物1-HOF溶於不同溶劑中的動態學。我們發現9F分子在非極性正己烷溶液中的螢光衰減曲線包含了兩個指數函數衰減，其主要的衰減生命期為~ 110 ps，而另一長時間的衰減生命期為1.5 ns。在極性二甲基亞碸溶液中，螢光衰減生命期為15 ns。1-HOF分子在非極性正己烷溶液中的螢光衰減曲線包含了短時間的衰減過程（時間常數小於儀器的時間解析度）及長時間的衰減過程（時間常數約為1.1 ns）。配合高階理論計算的結果，我們發現羰基非平面振動路徑對於笏酮分子的激發態緩解過程具有極大影響。 第二主題在於利用量子化學原理對咔唑衍生物2,7-DMVECz及3,6-DMVECz分子在法蘭克-康登組態（Franck-Condon，FC state）、第一激發單重態（the first singlet state，S1）和過渡組態（Transition State，TS）進行結構最佳化及激發態能量的理論計算。計算的結果顯示，3,6-咔唑分子衍生物具有經由碳碳單鍵轉動的有效系統間轉換而去活化的特性;然而在2,7-咔唑分子衍生物中，由於電子可完整地在分子內共振而造成原先在基態易轉動的碳碳單鍵在激發態具有較剛硬而不易轉動的雙鍵特性，因而導致其無法在激發態產生有效的去活化過程。我們的計算結果可以合理解釋在2,7-DPVTCz及3,6-DPVTCz分子所觀測到其螢光量子產率（ΦF）的極大差距（前者ΦF = 0.5而後者ΦF ~ 0.01）。

This thesis contains two subjects. The first subject is to study the photophysics and photochemistry of 9-Fluorenone（9F）and 1-Hydroxy-9-Fluorenone（1-HOF）in solutions with different polarity. The second subject is to perform quantum-chemical calculations for excited states of 2,7-DMVECz and 3,6-DMVECz using Gaussian03 software. For the first subject, the steady-state and time-resolved spectroscopy have been investigated for 9F and 1-HOF dissolved in polar and non-polar solvents. The time-resolved fluorescence spectra of 9F and 1-HOF were measured using the techniques of Time-Correlated Single Photon Counting（TCSPC）with excitation wavelengths in the range of 375 - 435 nm and fluorescence detected in the wavelength range of 430 – 700 nm. The TCSPC results of 9F show that two distinct transient components are involved in n-Hexane with the decay time constants of ~ 110 ps and ~ 1.5 ns, whereas only one component was observed in polar solvent （DMSO）with the decay time constant of ~ 15 ns. However, in the case of 1-HOF in n-Hexane the relaxation dynamics were found to involve only single exponential decay function with the decay time constant of ~ 1.1 ns, indicating the significance of C=O out of plane bending motion affecting the observed excited-state dynamics. The observed dynamics can be rationalized with the results obtained from high-level theoretical calculations. For the second subject, we performed a quantum-chemical calculations for the excited states of 2,7-DMVECz and 3,6-DMVECz.We also performed single-point energy calculations by using TDDFT method to obtain the potential energy surface along the bridged CC bond twisting coordinate. We found that the intersystem crossing deactivation activated in the 3,6-linked carbazole is efficient through the twisting motion of the bridged CC single bond whereas this electronic relaxation is inefficient in the 2,7-linked carbazole because extensive □-conjugation of the orbitals give the bridged CC bond a double-bond character. Therefore, the calculated results account for the much smaller values of Φf observed for the 3,6-linked carbazole then the 2,7-linked carbazole.