Synthesis of new kinds of reactive azo dyes and their application for fibre-optical pH-measurements

The aim of these investigations was the synthesis of a new kind of reactive azo dyes and their application as reversible pH-sensors. For binding of the dyes to a polymer matrix acetal bonding was introduced as a new method. The required azo dyes containing a formyl group were synthesised by two different routes: by introducing this functional group to a suitable substituent within pre-formed azo dyes, or to the dye precursors. Using polyvinyl alcohol and its co-polymers as matrix materials, acetalisation of the formyl groups of the dye by the 1,3-alternating hydroxy groups of the polymer can take place-forming a stable six-membered 1,3-dioxane ring. These dye-polymer composites can be used directly for thin film preparation. The obtained sensor membranes exhibit very good response behaviour and excellent long term stability, even under strongly basic conditions. These membranes turned out to be promising materials for an in-situ monitoring of aggressive environments, e.g. in concrete. (C) 2003 Elsevier Ltd. All rights reserved.