New ON–OFF type Ca2+-selective fluoroionophore having boron–dipyrromethene fluorophores

A new fluorogenic ionophore has been prepared by conjugating calix[4]-crown-5 ether with boron–dipyrromethene fluorophore. The ionophore exhibited a pronounced selective ON–OFF type response toward Ca2+ ions over other physiologically important metal ions of Na+, K+, and Mg2+. The interaction with Ca2+ ions resulted in very efficient quenching of fluorescence at 507 nm excited by relatively long wavelength irradiation at 480 nm. The selectivity ratios toward Ca2+ ions over other tested physiologically important metal ions were larger than 180 in aqueous 95% MeOH solution.