Fluorescent properties of an azacrown-containing styryl derivative of naphthopyran: ion-binding response and photochemical switching off

Abstract

The fluorescent properties of a recently synthesized photochromic naphthopyran containing a 1-aza-15-crown-5 moiety (1b) and its crownless analogue (1a) were studied. 1b emits fluorescence with a maximum at 528 nm, quantum yield 0.1 and characteristic lifetime 2.4 ns (in acetonitrile at room temperature). Its luminescence could be switched off photochemically in two ways using two parallel photochemical reactions characteristic for this type of naphthopyran. The first way is the irreversible trans–cis photoisomerization of a closed form (“stilbene-like reaction”). The second way is the thermally reversible reaction of closed form transition to the open form (“chromene-like reaction”). The fluorescence of 1b is quenched by alkali earth metal cations by the mechanism of static quenching. Stability constants for 1 : 1 complexes of 1b with Mg²⁺ and Ba²⁺ determined from Stern–Volmer plots are in agreement with that obtained by UV spectroscopy.