Enhancing the Photostability of Arylvinylenebipyridyl Compounds as Fluorescent Indicators for Intracellular Zinc(II) Ions.

Arylvinylenebipyridyl (AVB) ligands are bright, zinc(II)-sensitive fluoroionophores. The applicability of AVBs as fluorescent indicators for imaging cellular zinc(II), however, is limited by low photostability, partially attributable to the photoisomerization of the vinylene functionality. Two configurationally immobilized (i.e., "locked") AVB analogues are prepared in this work. The zinc(II)-sensitive photophysical properties and zinc(II) affinities of both AVBs and their locked analogues are characterized in organic and aqueous media. The zinc(II) sensitivity of the emission is attributed to the zinc(II)-dependent energies of the charge transfer excited states of these compounds. The configurationally locked ligands have improved photostability, while maintaining the brightness and zinc(II) sensibility of their AVB progenitors. The feasibility of the "locked" AVB analogues with improved photostability for imaging intracellular Zn(II) of eukaryotic cells using laser confocal fluorescence microscopy is demonstrated.