Squeezing Fluorescent Dyes into Nanoscale Containers—The Supramolecular Approach to Radiative Decay Engineering

Abstract

A review. Supramol. radiative decay engineering allows systematic variations of the radiative decay rates, and therefore changes in the fluorescence lifetimes and intensities. Depending on whether fluorescent dyes are immersed in macrocyclic host mols. with low or high polarizability, reduced or enhanced fluorescence lifetimes may result. Solvatochromic probes to "measure" the polarizability inside such mol. container compds. are now at hand. Cucurbiturils, for example, are water-sol. host mols., which possess a cavity with an exceptionally low polarizability, close to the gas phase. Placing fluorescent dyes inside cucurbiturils allows one to create in aq. soln. a unique microenvironment, which approaches that of the gas phase and leads to unprecedented photophys. behavior. Accordingly, complexation by cucurbituril leads to prolonged fluorescence lifetimes, for 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) up to 1 μs, the same as that found in the gas phase. [on SciFinder(R)]