SYNTHESIS OF REACTIVE VINYLSULPHONYL AZO DYES FOR APPLICATION IN OPTICAL PH SENSING

This work describes the application of a synthon (GM1) capable of form ing a variety of reactive azo dyes useful as pH indicators. GM1 posses ses two functional groups, namely (a) an amino group which allows diaz o coupling to form an indicator chromophore, and (b) a 2-hydroxyethyls ulphonyl group which, after activation, allows its immobilization on c ellulose. GM] has been diazo coupled with various aromatic phenols and amines to give a variety of pH probes. After the 2-hydroxyethylsulpho nyl group has been converted into a reactive vinylsulphonyl group, the dye has been covalently linked to the hydroxy groups of cellulose. We use a novel type of a transparent solid film consisting of a polyeste r support covered with a thin layer of cellulose acetate which, during immobilization, is converted into cellulose. Cellulose membranes colo ured with such pH indicating dyes can be applied for optical pH sensin g. All dyes are characterized, both in dissolved and immobilized form, in terms of optical properties in the acid and conjugate base form, p K(a) values and indicator properties. Semiempirical AM1 calculations h ave been performed in order to compute deprotonation energies of three representative dyes, and data were compared with experimental pK(a)'s