We report the chemistry of a dual hydrogen bonding network that activates carbonyl group for covalent capture and fluorescence detection of toxic cyanide anion. Hydrogen bonding is a prominent example of non-covalent interactions, which has been widely exploited for functional group activation, self-assembly, and supramolecular chemistry. Imidazole holds a unique position within this context, since it could (i) function as both hydrogen bonding donor (HBD) and acceptor (HBA), and (ii) tautomerize to take the role of either HBD or HBA (and even both) under proper structural setting. Taking advantage of this distinctive functional feature of imidazole, we have built a series of new fluorescent turn-on probe molecules for toxic CN<sup>-</sup> ion. One challenging aspect of this chemistry is the involvement of undesired Brønsted acid-base reaction, which disrupts the N-H…O=C hydrogen bonding contact to elicit strong background fluorescence signal and significantly compromise the selectivity. We have taken a systematic approach of installing multiple HBD/HBA groups around the imidazole core to reinforce the HBD…HBA contact and shift the equilibrium to the desired tautomer for highly sensitive, selective, and rapid detection of CN<sup>-</sup>. A combination of spectroscopic, X-ray crystallographic, and kinetics studies provide significant insights into the underlying structure-property-reactivity relationship of this chemistry.

Tightly-knit dual hydrogen bonding for fluorescence turn-on detection of cyanide: Evolving design principles and synthetic implementations

2019 Spring National Meeting

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