The formation of fluorescent alkali metal and alkaline earth complexes by 4-(2-{10-[2-(1,4-thiazinan-4-yl)ethyl]-9-anthryl}ethyl)thiomorpholine in acetonitrile

Abstract

<jats:p>The formation of fluorescent alkali metal and alkaline earth complexes of 1-(2-{10-[2-piperazinoethyl]-9-anthryl}ethyl)piperazine (1) and alkaline earth complexes by 4-(2-{10-[2-(1,4-thiazinan-4-yl)ethyl]-9-anthryl}ethyl)thiomorpholine (2) in acetonitrile is reported. Both (1) and (2) have ‘fluorophore–spacer–receptor’ structures in the sequences ‘anthracene–dimethylene–piperazine’ and ‘anthracene–dimethylene–thiomorpholine’, respectively. Complexation by alkali metal ions and alkaline earth ions, Mm+, modulate photoinduced electron transfer (PET) to increase the fluorescence of (1) and complexation of alkaline earth ions similarly increases the fluorescence of (2). The two receptors of (1) and (2) may either complex Mm+ singly to form [ML]m+ or cooperatively to form a ‘sandwich’ complex [ML′]m+ characterized together by complexation constant K1 and quantum yield φ1. They may also complex two Mm+ in [M2L]2m+ characterized by K2 and φ2. Typical data are exemplified for (1) and Mm+ = Na+ by K1 = 1.33 × 105 dm3 mol–1 (φ1 = 0.02) and K2 = 4.20 × 102 dm3 mol–1 (φ1 = 0.07), for (1) and Mm+ = Ca2+ by K1 = 3.2 × 106 dm3 mol–1 (φ1 = 0.34) and K2 = 1.32 × 104 dm3 mol–1 (φ2 = 0.54), and for (2) and Mm+ = Ca2+ by K1 = 2.29 × 104 dm3 mol–1 (φ1 = 0.20) and K2 = 8.0 × 102 dm3 mol–1 (φ2 = 0.57) at 298.2 K and I = 0.05 mol dm–3 (NEt4ClO4). These data are compared with those for the alkaline earth complexes of 4-{2-[10-(2-morpholinoethyl)-9-anthryl]ethyl}morpholine. In 40 : 60 (v/v) 1,4-dioxan/water, protonation modulates PET to increase the fluorescence of (1)H44+ and (2)H22+. (The pKa values of (1)H44+ are 9.02, 8.06, 4.32, and 2.96 at 298.2 K and I = 0.05 mol dm–3 (NEt4ClO4).) The syntheses of (1) and (2) are reported.</jats:p>