A two-photon fluorescent probe based on a ruthenium(II) vinyl complex is capable of selectively detecting carbon monoxide in cells and ex vivo using mice with a subcutaneous air pouch as a model for inflammation. This probe combines highly selective and sensitive ex vivo detection of endogenous CO in a realistic model with facile, inexpensive synthesis, and displays many advantages over the widely used palladium-based systems.

A new family of robust, non-toxic, water-compatible ruthenium(II) vinyl probes allows the rapid, selective and sensitive detection of endogenous carbon monoxide (CO) in live mammalian cells under normoxic and hypoxic conditions. Uniquely, these probes incorporate a viscosity-sensitive BODIPY fluorophore that allows the measurement of microscopic viscosity in live cells via fluorescence lifetime imaging microscopy (FLIM) while also monitoring CO levels. This is the first example of a probe that can simultaneously detect CO alongside small viscosity changes in organelles of live cells. Carbon monoxide (CO) has long been associated with its toxicity, however, this colourless and odourless gas also plays a key role in cellular messaging. [1] Its anti-inflammatory, antiproliferative, anti-apoptotic and anti-coagulative properties are now recognised. Intriguingly, under pathophysiological conditions (e.g., inflammation) CO production in cells increases, [2] and the real-time monitoring of these changes could potentially provide diagnostic information. Haemoglobin is required as a substrate for CO production in vivo and the haem oxygenases (HO-1 and HO-2) play a key role in the generation of this gas in mammals. Emerging evidence suggests that the increased generation of HO-derived CO plays a critical role in the resolution of inflammatory processes and alleviation of cardiovascular disorders, [3] which has driven interest in CO-releasing molecules (CORMs) for therapy. [4] A major obstacle is the lack of effective methods to track CO in biological systems in real time. [5] Imaging with emissive probes has emerged as one of the most powerful techniques to detect biologically important molecules. However, designing selective CO probes for the cellular environment is challenging, with its wide range of reactive species and variation in pH. He [6] and Chang [7] pioneered two very different

Optical sensing offers a low‐cost and effective means to sense carbon monoxide in air and in solution. This contribution reports the synthesis of a new series of vinyl complexes [Ru(CH=CHR)Cl(CO)(TBTD)(PPh3)2] (R=aryl, TBTD=5‐(3‐thienyl)‐2,1,3‐benzothiadiazole) and shows them to be highly sensitive and selective probes for carbon monoxide in both solution and air. Depending on the vinyl substituent, chromogenic and fluorogenic responses signalled the presence of this invisible, odourless, tasteless and toxic gas. Adsorbing the complexes on silica produced colorimetric probes for the ′naked eye′ detection of CO in the gas phase with a limit of detection as low as 8 ppm in some cases, while the release of the TBTD fluorophore allowed detection at much lower concentrations through the fluorescence response. Structural data were obtained by single‐crystal X‐ray diffraction techniques, while the photophysical behaviour was explored computationally using TD‐DFT experiments. The systems were also shown to be selective for CO over all other gases tested, including water vapour and common organic solvents. By introducing a poly(ethylene)glycol chain to the vinyl functionality, water compatibility was achieved and these non‐cytotoxic complexes were employed in the sensing of CO in HeLa cells, offering a simple and rapid system for sensing this gasotransmitter in this challenging medium.

As eries of new ruthenium(II) vinyl complexes has been prepared incorporating perylenemonoimide (PMI) units. This fluorogenic moiety was functionalised with terminal alkyne or pyridyl groups,a llowing attachment to the metal either as av inyl ligand or through the pyridyln itrogen. The inherentl ow solubility of the perylene compounds was improved through the design of poly-PEGylated (PEG = polyethylene glycol)units bearing aterminal alkyne or apyridyl group. By absorbing the compounds on silica, vapours and gases could be detected in the solid state. The reaction of the complexes [Ru(CH=CH-Per Im )Cl(CO)(py-3PEG)(PPh 3 ) 2 ] and [Ru(CH=CH-3PEG)Cl(CO)(py-Per Im )(PPh 3 ) 2 ]w ith carbon monoxide, isonitrile or cyanide was found to result in modulation of the fluorescenceb ehaviour.T he complexes were observed to display solvatochromic effects andt he interaction of the complexes with aw ide range of other species was also studied. The study suggestst hat such complexes have potential for the detection of gases or vapourst hat are toxic to humans.

+ These authors contributed equally.Supporting Information (consisting of TEM, EDS, TGA data for NP1 -NP4, selected NMR spectra, details of the Signer molecular mass determination apparatus and crystallographic data for 21) is available on the WWW at http://.