Highly sensitive salicylic fluorophore for visual detection of picomole amounts of Cu2+

Abstract

Four new fluorophores containing multiple fluorogenic branches of phenylene-ethynylene and salicylic acid Cu²⁺ binding sites are synthesized and evaluated as Cu²⁺ sensors in aqueous media. The fluorophore, F4, having a triphenylamine core and three fluorogenic branches, possesses superior sensitivity, selectivity and emission properties for fluorescence quenching detection of Cu²⁺. This fluorophore exhibits the highest Cu²⁺ quenching sensitivity in aqueous solution; K_sv = 5.79 × 10⁶ M⁻¹. The relatively high fluorescence emission of this fluorophore provides excellent visual contrast in a solid state paper-based sensor that enables naked eye detection of Cu²⁺ at the picomole level.