Simple naphthalimide based anion sensors: deprotonation induced colour changes and CO2 fixation

The 4-amino-1,8-naphthalimide based chemosensors 2, 4 and 6 show striking green-to-purple colour changes due to the deprotonation of the 4-amino moiety on interaction with strongly basic anions such as F⁻: these colour changes reverse gradually with time due to the fixation of atmospheric CO₂ (as HCO₃⁻) yielding 1:1 adducts as demonstrated by X-ray crystallography.