Towards the development of controllable and reversible 'on-off' luminescence switching in soft-matter; synthesis and spectroscopic investigation of 1,8-naphthalimide-based PET (photoinduced electron transfer) chemosensors for pH in water-permeable hydrogels

The synthesis of the pH PET sensors 1 and 2 is described. These molecules display 'on-off' switching in their fluorescence as a function of pH in aqueous solution. From the luminescent changes pK(a) values of 8.4( +/- 0.1) and 6.3( +/- 0.1) were determined respectively. These compounds were incorporated into poly[ methylmethacrylate-co-2-(hydroxyethylmethacrylate)]-based hydrogels and the luminescent properties of the resulting polymeric films were investigated using confocal laser-scanning microscopy. Both sensors showed substantial luminescent switching in the soft-matter, where the emission was 'switched off' after treating the hydrogels with alkaline solution and 'switched on' under acidic conditions.