Emergence of Colorimetric Chemosensor Ability of Metal Ions in TCNQ Polyester by Postfunctionalization

Postfunctionalization of the 7,7,8,8-tetracyano-1,4-quinodimethane (TCNQ) polyester by a [2+2] cycloaddition-cycloreversion process with an aniline-activated alkyne provided the colorimetric chemosensor ability of metal ions. The precursor TCNQ polyester did not show any spectral changes upon the addition of Fe3+ and Ag+ ions, whereas the postfunctionalized polyester displayed well-defined color changes due to the recognition of these metal ions. For example, the Fe3+ ion was recognized by the anilino nitrogen atoms, resulting in the disappearance of the charge-transfer (CT) band. In contrast, the Ag+ ion was recognized by the cyano nitrogen atoms due to the effective multivalent coordination, leading to the bathochromic shift in the CT band. The control experiments using the monomeric model compound suggested that the visual distinction between these two metal ions was achieved by the polymer effect.