Proton transfer dynamics in a polar nanodroplet: ESIPT of 4'-n,n-dimethylamino-3-hydroxyflavone in AOT/alkane/water reverse micelles

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• 作者：Deborin Ghosh^a ; Shaikh Batuta^b ; Naznin Ara Begum^b ; Debabrata Mandal^a ; ^{dmandal.chemistry@gmail.com}
• 刊名：Journal of Luminescence
• 出版年：2017
• 出版时间：April 2017
• 年：2017
• 卷：184
• 期：Complete
• 页码：64-73
• 全文大小：2173 K
• 卷排序：184

文摘

The excited state intramolecular proton transfer (ESIPT) of the well-known fluorophore 4'-N,N-Dimethylamino-3-hydroxyflavone (DMA3HF) was studied in AOT/n-heptane/water reverse micelle solutions. For DMA3HF molecules located inside the AOT encapsulated polar nanodroplets, ESIPT from excited enol (E*) to tautomer (T*) forms was markedly inhibited, yielding time-constants of ≥100 ps, and followed the same trend as solvent relaxation when the ratio W= [H2O]/[AOT] was varied. At W=0, the DMA3HF molecules were attached to the ionic AOT headgroups via strong intermolecular H-bonding, which hindered ESIPT. Addition of water changes the situation radically: water molecules form stronger H-bonds with AOT headgroups, displacing the DMA3HF, which are instead engaged in intermolecular H-bonded complexes of the type [DMA3HF···water]. ESIPT of these complex-bound fluorophores involves substantial rearrangement of H-bonding, and is coupled to solvation dynamics. With increasing W-value, solvation becomes faster, and so does ESIPT, reducing the yield of E* species. At the same time, the local environment within the nanodroplets become more more polar with gradual accumulation of water, which causes a monotonic red-shift of the E* emission peak.