Four naphthalenediimide colorimetric pH indicators were synthesized with N,N-dimethylethyleneamine at the imide positions and 5- to 7-membered heterocyclic rings bay positions, namely pyrrolidine, morpholine, piperidine azepane. The are constructed in a modular receptor–spacer–fluorophore–spacer–receptor format based on photoinduced electron transfer (PET) design. compounds studied by UV–visibl...