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 (φ_f) for (1a–c) were negligibly small (0.009–0.014). The phosphorescence quantum yields (φ_p) 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 φ_f/φ_p values increased with an increase in the binding ability of alkaline-earth-metal cations to (1a–c). Although φ_p values of (1a–c) slightly decreased on addition of alkali-metal cations, the exception being a slight enhancement of φ_p for (1a)–Cs⁺, (1b)–Cs⁺, and (1b)–Rb⁺ systems, no fluorescence peak appeared.