As scientists in recent decades have discovered, selenium is an important trace element in life. The element is now known to play an important role in biology as an enzymatic antioxidant. In this case, it sits at the active site and converts biological hydrogen peroxides to water. Mimicking this reaction, chemists have synthesized several organoselenium compounds that undergo redox transformations. As such, these types of compounds are important in the future of both medicinal and materials chemistry. One main challenge for organochalcogen chemists has been to synthesize molecular probes that are soluble in water where a selenium or tellurium center can best modify electronics of the molecule based on a chemical oxidation or reduction event. In this Account, we discuss chemists' recent efforts to create chalcogen-based chemosensors through synthetic means and current photophysical understanding. Our work has focused on small chromophoric or fluorophoric molecules, in which we incorporate discrete organochalcogen atoms (e.g., R-Se-R, R-Te-R) in predesigned sites. These synthetic molecules, involving rational synthetic pathways, allow us to chemoselectively oxidize compounds and to study the level of analyte selectivity by way of their optical responses. All the reports we discussed here deal with well-defined and small synthetic molecular systems. With a large number of reports published over the last few years, many have notably originated from the laboratory of K. Han (P. R. China). This growing body of research has given chemists new ideas for the previously untenable reversible reactive oxygen species detection. While reversibility of the probe is technically important from the stand-point of the chalcogen center, facile regenerability of the probe using a secondary analyte to recover the initial probe is a very promising avenue. This is because (bio)chalcogen chemistry is extremely rich and bioinspired and continues to yield important developments across many scientific fields. Organochalcogen (R-E-R) chemistry in such chemical recognition and supramolecular pursuits is a fundamental tool to allow chemists to explore stable organic-based probe modalities of interest to develop better spectroscopic tools for (neuro)biological applications. Chalcogen donor sites also provide sites where metals can coordinate, and facile oxidation may extend to the sulfone analogues (R-EO2-R) or beyond. Consequently, chemists can then make use of reliable reversible chemical probing platforms based on the chemical redox properties valence state switching principally from 2 to 4 (and back to 2) of selenium and tellurium atoms. The main organic molecular skeletons have involved chemical frames including boron-dipyrromethene (BODIPY) systems, extended cyanine groups, naphthalimide, rhodamine, and fluorescein cores, and isoselenazolone, pyrene, coumarin, benzoselenadiazole, and selenoguanine systems. Our group has tested many such molecular probe systems in cellular milieu and under a series of conditions and competitive environment...

Annulated BODIPY chalcogenide (Se, Te) systems were synthesized from their respective bis(o-formylphenyl)dichalcogenide intermediates. The annulated BODIPY selenide product was confirmed by X-ray diffraction. The red-shifted telluride version was found to be sensitive and selective for hypochlorite detection, reversible upon treatment with biothiols.

A diselenide-based BODIPY probe was prepared; it was found to be sensitive and selective for superoxide in giving [-Se(O)Se(O)-] oxidation. Probing was reversible through the use of biothiols; (77)Se NMR and other types of spectroscopy were employed. Practical medicinal utility was demonstrated in MCF-7/ADR cancer cells.

The synthesis and characterization of substituted benzimidazolin‐2‐selones (4c–4d) and ‐tellone (4i) are reported. Upon reaction with halogens (I2, Br2, and Cl2), these selones and tellone yield dihaloselones/tellone (5c–5i). The reaction of dihaloselones with elemental tellurium/tin/bismuth leads to the formation of selone‐coordinated monomeric tellurium tetrahalides, tellurium dibromide (8), tin tetrahalides, and bismuth triiodide adducts (7a–7g), respectively. The structures of the tellurium tetrahalide (7a, 7d, and 7g), tellurium dibromide (8), tin tetrahalide, and bismuth triiodide adducts have been established by single‐crystal X‐ray analysis. The bismuth triiodide adduct is the first neutral tetrameric structure with selones. The bismuth adduct has been used as a single‐source precursor for the synthesis of bismuth selenide (Bi2Se3) nanoparticles, which were characterized by powder XRD patterns. The TEM images show the hexagonal shape of the nanoparticles.

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