Cation-controlled emission of crowned acetophenone

Abstract

Effects of alkali- and alkaline-earth-metal cations on the emission properties of 4′-acetylbenzo-15-crown-5 (1a), 4′-acetylbenzo-18-crown-6 (1b), 4′-acetylbenzo-21-crown-7 (1c), and 3,4-dimethoxyacetophenone (2) have been studied in degassed EtOH–MeOH (4:1 v/v) glasses at 77 K. The fluorescence quantum yields (φf) for (1a–c) were negligibly small (0.009–0.014). The phosphorescence quantum yields (φp) for (1a), (1b), (1c), and (2) were 0.26, 0.47, 0.51, and 0.52, respectively, being dependent on the ring size of the crown ether moiety. Binding of alkaline-earth-metal cations decreased the phosphorescence peak at 470 nm concomitant with an appearance of the fluorescence peak at 365 nm. The φf/φp values increased with an increase in the binding ability of alkaline-earth-metal cations to (1a–c). Although φp values of (1a–c) slightly decreased on addition of alkali-metal cations, the exception being a slight enhancement of φp for (1a)–Cs+, (1b)–Cs+, and (1b)–Rb+ systems, no fluorescence peak appeared.