Reorganization of Self-Assembled Dipeptide Porphyrin J-Aggregates in Water鈥揈thanol Mixtures

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• 作者：Raquel Teixeira ; Suzana M. Andrade ; Vanda Vaz Serra ; Pedro M. R. Paulo ; Antonio S谩nchez-Coronilla ; Maria G. P. M. S. Neves ; Jos茅 A. S. Cavaleiro ; S铆lvia M. B. Costa
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：March 1, 2012
• 年：2012
• 卷：116
• 期：8
• 页码：2396-2404
• 全文大小：510K
• 年卷期：v.116,no.8(March 1, 2012)
• ISSN：1520-5207

文摘

The self-assembly of a neutral meso-methoxyphenylporphyrin functionalized with a dipeptide glycilglycine substituent (MGG) in water and in water鈥揺thanol mixtures was studied by absorption and fluorescence spectroscopy. In water, hydrophobic interactions and the noncovalent intermolecular hydrogen bonding between the terminal carboxylate group of one porphyrin and the hydrogen atoms of the pyrrolic nitrogens of another porphyrin originate nonspecific disorganized H- and J-aggregates. The addition of ethanol (0.1鈥?5% v/v) to the water creates small clusters within which porphyrin J-aggregates reorganize as revealed by a narrow intense band detected by the Rayleigh light scattering (RLS) at 443 nm. Similar phenomenology is detected in SDS premicellar aggregates. Computational DFT calculations of a model dimer formation stabilized via intermolecular hydrogen bonding estimate an energy gain of 鈭?2 kJ mol^鈥? and a center-to-center and interplane distances between porphyrin moieties of 16.8 and 3.7 脜, respectively. The kinetics of the J-aggregate formation could be fitted with a time-dependent model, and an activation energy of 96 kJ mol^鈥? was estimated. The aggregate's morphology of MGG was followed by transmission electron microscopy (TEM) which showed rod-type structures of 5鈥? 渭m evolving to spherical particles with increased ethanol content. Similar images and sizes were obtained in analogous samples using fluorescence lifetime imaging microscopy (FLIM) and dynamic light scattering (DLS). The formation of excitonically coupled supramolecular MGG structures of brickwork or staircase types is proposed in these water鈥揺thanol mixtures.