Pseudoaromaticity-driven, transition metal detection by squaraine-derived enol phosphonium ylide chemodosimeters.

The addition of PBu to -substituted dianiline squaraine dyes leads to bench stable ylides. Exposure to a metal analyte in solution, results in P abstraction and rapid disruption of the ylide conjugation to promote reversion back to the squaraine dye giving an immediate turn-on colorimetric response. The stoichiometric sensitivity and accessibility of these chemodosimeters constitute effective organic dyes for trace transition metal detection.