Bichromophoric naphthalene derivatives of ethylenediaminetetraacetate: Fluorescence from intramolecular excimer, protonation and complexation with Zn2+and Cd2+

Lorena Machi, Hisila Santacruz, Mario Sánchez, Motomichi Inoue

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Abstract

Chelating water-soluble bichromophoric compounds were designed by linking two naphthalene rings with an ethylenediaminetetraacetate (edta) chain through amide linkages, and characterized by fluorescence and NMR spectroscopies: the bichromophores studied were 1,4-bis(methylenecarboxy)-1,4-bis(N-1- naphthylacetamide)-1,4-diazabutane, abbreviated as (edta1nap)H2, and the corresponding 2-naphthylacetamide, abbreviated as (edta2nap)H2. Completely deprotonated species M2-that formed in basic solution exhibited an intense emission from intramolecular excimer at 440 nm for (edta1nap)2-and 404 nm for (edta2nap)2-, while emission from monomeric naphthyl group was comparatively very weak. Geometry optimization based on Density Functional Theory showed that two naphthyl groups in an M2-molecule faced each other in such a way that an intramolecular excimer was readily formed by light excitation. Protonation on amino nitrogen affected monomer-excimer interconversion in different modes for the two compounds: the excimer emission was strengthened in the resulting (edta1nap)H-, but was weakened in (edta2nap)H-. Upon coordination with Zn2+, the excimer band of (edta1nap)2-as well as (edta2nap)2-was strengthened in a linear manner with [Zn]/[L]; concurrently monomer emission was weakened. Coordination of (edta2nap)2-with Cd2+resulted in a large decrease in the excimer emission, while the emission of (edta1nap)2-was almost unchanged. The formation of intramolecular excimer, which is highly sensitive to protonation and complexation, is due to the strictly defined molecular conformation. © 2006 Taylor & Francis.
Original languageAmerican English
Pages (from-to)561-569
Number of pages9
JournalSupramolecular Chemistry
DOIs
StatePublished - 1 Oct 2006

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