Synthesis, structures and properties of self-assembling quaternary ammonium dansyl fluorescent tags for porous and non-porous surfaces

A series of H₂O and/or EtOH soluble, self-assembling quaternary ammonium salts containing a dansyl (DNS) fluorescent moiety suitable for attachment to both porous ([DNS–NH–(CH₂)₃–NMe₂–R⁺][X⁻] (2; R = –Si(OMe)₃, X⁻ = Cl⁻) and non-porous (3a; R = –PO(OEt)₂, 3b; –PO(Oi-Pr)₂, 3c; –(PO(OH)₂, X⁻ = Br⁻), 4; ([DNS–NH–(CH₂)₃–NMe₂–(CH₂)₃–NH(CH₂PO(OEt)₂)₂⁺][Br⁻], 5; R = –((CH₂)₃SCOCH₃, X⁻ = Cl⁻), 6a; (R = –(CH₂)_nO(C₆H₄)CO(C₆H₅), n = 3, X⁻ = Br⁻, 6b; n = 3, X⁻ = Cl⁻, 6c; n = 3, X⁻ = I⁻, 6d; n = 4, X⁻ = Br⁻, 6e; n = 4, X⁻ = I⁻, 6f; n = 6, X⁻ = Br⁻, 6g; n = 6, X⁻ = Cl⁻, 6h; n = 6, X⁻ = I⁻), 7; (R = –CH₂–CHCH₂, X⁻ = Br⁻) surfaces were prepared from the precursor dansyl amine (1; DNS–NH–(CH₂)₃–NMe₂). Compounds 1–7 were characterized by NMR (¹H, ¹³C, ²⁹Si (2), ³¹P (3a–c, 4)) spectroscopy, HRMS, UV-Vis and fluorescence spectroscopy. Additional characterization of compounds 1 and 7 were carried out by X-ray structure determinations. Physical attachment of compound 2 to cotton surfaces after immersion in solutions containing fluorescent dyes was verified by exposure to UV light and by complexation with bromo-phenol blue that rendered the surfaces visibly blue in colour. Phosphorus containing dansyl fluorescent dye, 3c, was attached to a stainless steel surface by exposure to an aqueous solution containing this dye, resulting in the formation of a self-assembled fluorescent monolayer. UV cure of plastic surfaces (polypropylene, silicon medical tubing) coated with compound 6a resulted in the covalent attachment of the dyes.