6-Aminocoumarin-naphthoquinone conjugates: design, synthesis, photophysical and electrochemical properties and DFT calculations

Journal of the Brazilian Chemical Society

Fabio S. Miranda¹  Célia M. Ronconi¹  Mikaelly O. B. Sousa¹  Gleiciani Q. Silveira¹  Maria D. Vargas¹ 

[1] ,Universidade Federal Fluminense Instituto de Química Niterói RJ ,Brazil

关键词: aminonaphthoquinone;    aminocoumarin;    TD-DFT calculations;    fluorescence;   

DOI  :  10.5935/0103-5053.20130279

来源: SciELO

【 摘 要 】

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...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 (S0) and excited (S1) 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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