The Fluorescence of a Chelating Two-Photon-Absorbing Dye is Enhanced with the Addition of Transition Metal Ions but Quenched in the Presence of Acid

摘要

A pseudo-symmetric two-photon absorbing dye (1) containing a central piperazine unit substituted with (benzothiazol-2-yl)-9,9-diethylfluoren-2-yl pendant groups has been synthesized and characterized. The molecule has a two-photon-absorption cross-section of σ_2 =140 GM in tetrahydrofuran at ～ 740 nm and shows significant solvatochromism in the excited-state fluorescence spectra. The emission spectra broaden and the maxima bathochromically shift from 411 nm to 524 nm in n-hexane and acetonitrile, respectively. Moreover, the central piperazine moiety serves as a potential chelation site for ions. Addition of copper(Ⅰ) hexafluorophosphate and zinc(Ⅱ) triflate in acetonitrile indicate ground-state complexation with a shift in the emission maximum from 524 nm to 489 nm and 487 nm, respectively. Interestingly, the newly formed Cu and Zn complexes are more strongly emissive than the free dye. Finally, addition of p-toluenesulfonic acid in tetrahydrofuran also blue-shifts the emission maximum, but the intensity is quenched. Due to the photophysical changes induced by addition of metal ions and protons, the dye shows promise as a potential sensor.