本論文系統性地設計與合成數個多叉及樹枝狀染料分子，希望藉由增加分子的共軛長度或是改變分子結構上具拉電子特性的官能基，以探討分子結構上的改變對雙光子吸收性質的影響。我們透過線性光學的量測結果得知模型分子的最大吸收波長與最大發射波長，進而選擇適當的標準品來求得各模型分子之螢光量子產率。至於非線性光學性質的部份，我們利用波長為790nm之(鈦：藍寶石)飛秒雷射作為光源以檢測雙光子激發螢光強度與激發光源強度間關係並由實驗結果證實在我們的實驗條件下所觀察到的螢光現象確實是經由雙光子吸收所引起的。此外，我們以Fluorescein作為標準品，藉由雙光子誘導螢光法以測定各模型分子之雙光子激發光譜圖。經由分析各模型分子之雙光子激發光譜行為與分子結構間的關聯性，可歸納出以下結果：[1]若延長分子整體的共軛長度對於提升雙光子激發截面有正面的影響；[2]若增加分子結構外圍的分支數目進而擴展成為樹狀型分子，其雙光子吸收效能可大幅度提升；[3]若在五叉型分子結構中導入不同之拉電子官能基，其提升雙光子激發截面的趨勢為：benzothiazole>1,3,4-oxadiazole；[4]若在對稱型樹狀分子結構中導入1,3,4-oxadiazole拉電子官能基會比導入thiazolothiazole更能有助於提升模型分子之雙光子吸收能力。 Several series of two-photon absorbing model chromophores with multi-branched and/or dendritic geometries were synthesized and characterized in the femtosecond and nanosecond time domain. The experimental results show that these model compounds exhibit strong two-photon activities within the spectral region of 700~850nm. It is also demonstrated that increasing the branch number within a molecule will lead to promoted two-photon absorptivity. Effective optical power restriction behaviors of these fluorophores were also investigated using nanosecond laser pulses and it was found that these dye molecules possess strong two-photon-assisted excited state absorption and could be potential candidates for broad-band optical limiters especially when against longer laser pulses.
