Bis(1-pyrenylmethyl)-2-benzyl-2-methyl-malonate as a Cu²⁺ Ion-Selective Fluoroionophore

A new malonate possessing two pyrene moieties was synthesized as a fluoroionophore, and its structure and fluorescence spectroscopic properties were investigated. When excited at 344 nm in acetonitrile/chloroform (9:1, v/v), the synthesized bispyrenyl malonate has the fluorescence of intramolecular excimer (λ_em = 467 nm) emissions and not a pyrene monomer emission (λ_em = 394 nm). A large absolute fluorescence quantum yield was obtained in the solid state (Φ_PL = 0.65) rather than in solution (Φ_PL = 0.13). X-ray crystallography analysis clarified the molecular structure and alignment of the bispyrenyl malonate in the crystal phase, elucidating its fluorescence spectroscopic properties. Such analysis also suggests there are intramolecular C-H···π interactions and intermolecular π···π interactions between the pyrenyl rings. Interestingly, the synthesized bispyrenyl malonate exhibits excellent fluorescence sensing for the Cu²⁺ ion. Remarkable fluorescence intensity enhancement was only observed with the addition of the Cu²⁺ ion.