期刊
JOURNAL OF THE BRAZILIAN CHEMICAL SOCIETY
卷 25, 期 1, 页码 133-142出版社
SOC BRASILEIRA QUIMICA
DOI: 10.5935/0103-5053.20130279
关键词
aminonaphthoquinone; aminocoumarin; TD-DFT calculations; fluorescence
资金
- FAPERJ [E-26/171.512.2010, E-26/110.692/2012, E-26/103.213/2011, E-26/103.084/2011]
Four novel 6-aminocoumarin-naphthoquinone conjugates were synthesized and their photophysical and electrochemical properties, investigated. 2-Chloro-3-(2-oxo-2H-chromen-6-ylamino)- 1,4-naphthoquinone 1 did not present appreciable fluorescence in solution in comparison with 6-aminocoumarin, 6-AC. In order to understand the reasons for the fluorescence quenching in this compound, two strategies were attempted. Firstly, compound 1 was N-methylated to remove the intramolecular N-H center dot center dot center dot O = C electrostatic interaction that maintained the two units fixed, but the emission properties of the product 2 were not significantly different from those of 1. Time-dependent density functional theory (TD-DFT) calculations of compounds 1 and 2 indicate that the fluorescence quenching is related to the electron acceptor character of the naphthoquinone ring. The second strategy, therefore, involved the substitution of the chlorine atom in position 2 of the naphthoquinone nucleus for different electron donor groups (compounds 3-5), but again the emission properties did not change significantly. To explain these experimental findings, TD-DFT calculations of the ground (S-0) and excited (S-1) states of all molecules in solution were carried out. The results suggest that the energy states in these conjugates are such that the fluorescent group (6-AC) donates electrons to the naphthoquinone LUMO resulting in an oxidative photoinduced electron transfer (oxidative-PET).
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