Taming fluorescent dyes with cucurbituril

Abstract

The potential of the supramolecular host molecule cucurbit[7]uril to serve as a stabilizing additive and enhancement agent was investigated for the following dyes in aqueous solution: rhodamine 6G, rhodamine 123, tetramethylrhodamine, cresyl violet, fluorescein, coumarin 102, pyronin B, pyronin Y, two cyanine 5 and one cyanine 3 derivative, and IR140 as well as IR144. For most cationic dyes photostabilization was established, and a pronounced thermal stabilization due to deaggregation and solubilization was observed for the xanthene dyes. The advantageous effects are attributed to the formation of inclusion complexes with different photophysical and photochemical properties. The complexation is accompanied by spectral shifts characteristic for the inclusion in a less polar environment, while the fluorescence quantum yields as well as the brightness show an increase, with few exceptions. As a consequence of the low polarizability inside the cucurbituril cavity, the fluorescence lifetimes of the included dyes increase substantially and systematically. Applications of the new photostabilizing additive for dye lasers, for prolonged storage of dye solutions, in scanning confocal microscopy, and fluorescence correlation spectroscopy are discussed.