Excited State Intramolecular Proton Transfer in π-Expanded Phenazine-Derived Phenols

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• 作者：Joanna Piechowska ; Kirsi Virkki ; Bart?omiej Sadowski ; Helge Lemmetyinen ; Nikolai V. Tkachenko ; Daniel T. Gryko
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：January 9, 2014
• 年：2014
• 卷：118
• 期：1
• 页码：144-151
• 全文大小：308K
• ISSN：1520-5215

文摘

Two previously inaccessible analogs of 10-hydroxybenzo[h]quinoline were prepared via a straightforward strategy comprising the formation of 蟺-expanded phenazines skeleton followed by C鈥揌 acetoxylation at position 10. Two bis-phenols possessing C₂ and D₂ symmetry were obtained in yields of 52% and 15%, respectively. The occurrence of excited state intramolecular proton transfer (ESIPT) was detected in all cases because steady state emission was observed only from the excited keto-tautomer. Additionally, a short-lived, 0.1 ps, emission decay was resolved by the femtosecond up-conversion technique at the blue side of the keto-tautomer emission band, 610 nm, and was attributed to the ESIPT, i.e., conversion from enol to keto tautomer. In comparison with the corresponding 10-hydroxybenzo[h]quinoline emissions, the emission spectrum of the 蟺-expanded phenazine analogues were weaker but displayed a characteristic bathochromically shift into NIR region. These phenazine analogues constitute one of largest heterocycles for which ESIPT was unambiguously detected.