Reduced dicyanovinyl dyes: A chromophore to be used for optical sensing in the red and near-infrared spectral range

Reduced dicyanovinyl dyes, a new type of pH-sensitive chromophores with absorption bands reaching into the near-infrared (near-IR) spectral range, are presented, Side-chain residues with different properties were attached to the chromophore backbone to influence the pK(a) values of the indicator dyes. The resulting dyes were suitable to be incorporated into lipophilic optical sensing bulk membranes (optodes) made from plasticized poly(vinylchloride), The characteristics of the indicators were studied in pH-sensitive membranes. Full signal reversibility for protonation and deprotonation and high chromophore stability were observed. As an example of application for ion-sensing, a calcium-selective optode is demonstrated. The dynamic measuring range for calcium was 10(-6)-10(-1) M in aqueous solutions, buffered at pH 2.7. The response behavior, short-time reproducibility, and stability of the optodes are discussed.