具有間位長碳鏈苯基之推拉電子鋅紫質分子於氧化鋁及二氧化鈦奈米薄膜上之飛秒螢光動力學研究

Abstract

本論文研究利用飛秒螢光上轉換技術量測具有間位長碳鏈之推拉電子基之鋅紫質分子，於氧化鋁與二氧化鈦固相奈米薄膜上之激發態緩解動力學。在本實驗中，我們分別量測大氣環境，與模擬染料敏化太陽能電池的乙腈浸潤環境之螢光瞬態光譜。藉由調控薄膜上之分子密度，來探討其間位長碳鏈結構之立體效應，對於紫質分子聚集行為所引發的能量轉移速率之影響。在大氣環境的實驗中發現到，長碳鏈取代基的確能夠有效降低分子間能量轉移速率，卻同時也影響電子注入的速率。推測其長碳鏈結構不僅影響分子間距，同時影響吸附於奈米粒子上的排列方式，改變了電子注入的途徑與速率。由溶液環境中的螢光瞬態光譜可以得知，溶劑分子對於防止紫質分子聚集的現象 有相當的影響。由濃度相近的氧化鋁薄膜實驗結果顯示，YD2-o-C5 與 YD2-o-C8 之排列形貌和YD2 與YD2-m-C5可能有所不同。但在濃度相近的二氧化鈦薄膜實驗中，所有的紫質分子卻有相似的行為。我們藉由量測不同分子密度下的薄膜螢光瞬態光譜，希望提供另一種求得電子注入速率常數與量子效率的的計算方式。

In this study, we investigated the excited-state relaxation dynamic of “push-pull” zinc porphyrins with alkyl-substitution at meso-position absorbed on the nanocrystalline semiconducting films. With femtosecond fluorescence up-conversion technique, we measured the transient fluorescence spectra of the films in air and in an environment containing acetonitrile. By controlling the molecular density of porphyrins absorbed on nanocrystalline films, we studied the energy transfer effects of porphyrin aggregation. The results in the air environment indicate that the intermolecular energy transfer process was effectively suppressed for porphyrins with ortho-substituted bulky groups. We found that the bulky side- chain groups also decrease the electron injection rate of porphyrins on TiO2 films. Our study reveals that long alkoxyl chains not only increase the intermolecular distance, but also affect the molecular arrangement on the thin-film surface. In the acetonitrile environment, our results show the important role of the solvent molecules on preventing the aggregation of porphyrins adsorbed on TiO2 films. The results of molecular density dependence indicate the morphology of YD2-o-C5 and YD2-o-C8 on Al2O3 films might be different from that of YD2 andYD2-m-C5. On TiO2 films, all porphyrins show similar concentration dependent behavior, suggesting that the morphology of porphyrins on TiO2 is drastically different from that on Al2O3 films. By examining the dynamics depending on the molecular densities, we provide a new model to evaluate the electron injection rates and quantum yield for dye/TiO2 films.