Synthesis and spectroscopic studies of diaza-8-crown-4-dinitrophenyl ethers

The macrocycles 3,7-bis(3-nitrophenyl)-1,5,3,7-dioxadiazocane 1 and 3,7-bis(4-nitrophenyl)-1,5,3,7-dioxadiazocane 2 were synthesised by a one-pot reaction with substituted nitroanilines and formaldehyde under acidic conditions. The same reaction with 2-nitroaniline yielded N, N’-(oxybis(methylene))bis(2-nitroaniline) 3 rather than 3,7-bis(2-nitrophenyl)-1,5,3,7-dioxadiazocane 4. The yellow powders 1–3 were characterised by ¹H/¹³C/¹⁵N NMR, FTIR and HRMS. The photophysical properties were studied by UV-visible absorption and steady-state fluorescence spectroscopy. Acid dissociation constants were determined by UV-visible absorption titrations in 1:1 (v/v) acetonitrile/water to be 0.80 and 3.1 for the meta- and para-substituted compounds 1 and 2, respectively. Compounds 1 and 2 were discovered to fluoresce in the solid-state, yellow and green, respectively, but not in solution. Density functional theory (DFT) calculations for 1–4 provide insight into the frontier molecular orbital energy levels. These compounds represent a new class of fluorescent heterocyclic building blocks for organic and supramolecular applications.