Li+ Selective Podand-Type Fluoroionophore Based on a Diphenyl Sulfoxide Derivative Bearing Two Pyrene Groups

New podand-type fluoroionophores having two pyrene moieties: 2,2′-bis(1-pyrenylacetyloxy)diphenyl sulfide (3), 2,2′-bis(1-pyrenylacetyloxy)diphenyl sulfoxide (4), and 2,2′-bis(1-pyrenylacetyloxy)diphenyl sulfone (5), have been synthesized by connecting two 1-pyrenecarbonylmethyl groups with the two hydroxy groups of 2,2′-dihydroxydiphenyl sulfide, sulfoxide, and sulfone, respectively. Their complexation behavior toward alkali metal ions was examined by fluorescence spectroscopy. Among these fluoroionophores, compound 4, having a sulfinyl group, showed high selectivity toward Li+.