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 (λem = 467 nm) emissions and not a pyrene monomer emission (λem = 394 nm). A large absolute fluorescence quantum yield was obtained in the solid state (ΦPL = 0.65) rather than in solution (ΦPL = 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.