The Formation of Fluorescent Alkali Metal and Alkaline Earth Complexes by 1-(2-{10-[2-Piperazinoethyl]-9-anthryl}ethyl)piperazine and Alkaline Earth Complexes by 4-(2-{10-[2-(1,4-Thiazinan-4-yl)ethyl]-9-anthryl}ethyl)thiomorpholine in Acetonitrile

Abstract

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, M^m+, 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 M^m+ 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 M^m+ in [M₂L]^2m+ characterized by K₂ and φ₂. Typical data are exemplified for (1) and M^m+ = 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 M^m+ = 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 M^m+ = 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 pK_a 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.