Yuan, L. et al. J. Am. Chem. Soc. advance online publication (6 January 2012).

Near-infrared light is highly advantageous for biological imaging thanks to its minimal photodamage, its capacity for deep tissue penetration and the minimal background autofluorescence that is produced by living tissue at this wavelength. Fluorescent dyes that absorb and emit in the infrared range exist, but often it is hard to design functional near-infrared sensors that switch on or off their fluorescence in response to a given metabolite. Yuan and colleagues describe a new type of near-infrared functional dyes called Changsha, which are hybrids of merocyanine A and benzoic acid. These compounds have a fluorescence on-off switching mechanism similar to that of rhodamine dyes, making them good candidates for near-infrared functional sensor design. The authors synthesized six Changsha dyes with slightly different photophysical characteristics and used one of them to develop a near-infrared sensor that turns on its fluorescence upon binding to endogenously produced HClO in living cells and mice.