Design, synthesis and sensor activity of a highly photostable blue emitting 1,8-naphthalimide

► Novel blue emitting 1,8-naphthalimide containing HALS fragment is synthesized. ► The compound is designed as a highly photostable PET based fluorescent sensor. ► The emission intensity of the fluorophore is enhanced substantially in acidic media. ► The naphthalimide sensor selectively detects Cu2+ ions. ► HALS unit considerably improves the sensor's photostability, sensitivity and selectivity.