Synthesis of naphthalimide-based indicator dyes with a 2-hydroxyethylsulfonyl function for covalent immobilisation to cellulose

A new approach for the synthesis of 2-hydroxyethylsulfonyl type indicator dyes has been introduced to the naphthalimide chemical structure. Thus, fluorescent indicator dyes can be obtained that can be covalently linked to cellulose used e.g. in optical sensor layers, textiles and wound dressings. The approach is tailored to be simple in synthesis and with a minimum number of steps required to obtain a highly functional and stable sensor material. Three different pH indicator dyes have been prepared and covalently immobilised to transparent cellulose layers. The pK_a values of the cellulose-immobilised dyes were found to be at around 3, 6 and 7, thus covering the physiologically relevant pH range. Using the 2-hydroxyethylsulfonyl group, covalent immobilisation of naphthalimides with various receptor functions may become possible.