Design Strategies for Water-Soluble Small Molecular Chromogenic and Fluorogenic Probes

The most often used strategies in designing small molecular chromogenic and fluorogenic probes for various analytes are studied. Most of the chromogenic and fluorogenic probes were constructed by using the fluorochromes such as anthracene, benzofurazan, BODIPY, coumarin, cyanine, naphthalene, quinoline, squaraine, and xanthene, and a lot of them exhibit fluorescence off-on or ratiometric (wavelength shifts) responses to an analyte via the photophysical processes like PET, ICT, or FRET. First, for practical applications of the probes in biochemical studies good water solubility is essential, because the usage of organic solvents usually destroys the normal function of biomolecules. Second, more probes with NIR features should be exploited. Unfortunately, most of the existing NIR fluorescent probes are derived from cyanine dyes, which suffer from poor stability. NIR chromogenic and fluorogenic probes with high stability and quantum yield as well as good water solubility are still expected.