New phosphinoyl-containing tetradentate heterocycles preorganised for metal ion binding were designed and prepared in high yields. The X-ray structures of two allied phosphinoyl-bearing 2,2′-bipyridyl and phenanthroline ligands, as well as closely related structures of 2,6-bis(diphenylphosphinoyl)pyridine and 9-(diphenylphosphinoyl)-1,10-phenanthroline-2-one, are reported. Complexes of nitrates of several lanthanides and trifluoroacetate of Eu(III) with two phosphinoyl-bearing 2,2′-bipyridyl and phenanthroline ligands were isolated and characterised. The first structures of lanthanide complexes with phosphinoyl-bearing 2,2′-bipyridyl and phenanthroline ligands are reported. The nature of the counter-ion is crucial for the coordination environment of the metal ion. The photophysical properties of the complexes differring in both the nature of the ligand and counter-ion were investigated. The photophysical properties of the complexes are strongly ligand- and counter-ion-dependent. Absorbance and luminescence excitation spectra of complexes showed main peaks in the UV range which correspond to the absorption of light by the ligand and these are ligand-dependent. Luminescence spectra of complexes show typical europium emission in the red region with a high quantum yield, which corresponds to the transitions ⁵D₀ → ⁷F_J (J = 0–6). The value of deviation of the components of ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₁ transitions from the inversion centre shows a larger dependence on the counter-ion than on the nature of the ligand. The value of the luminescence quantum yield is larger for europium complexes with 2,2′-bipyridyl-based ligands and NO₃ counter-ions than for complexes with phenanthroline-based ligands and NO₃ counter-ions. A low dependence of the luminescence lifetime of Eu complexes on the nature of the ligand has been demonstrated: values in the solid state were in the range 1.1–2.0 ms.

Due to postglacial isostatic uplift many stratified lakes, at different stages of isolation, are located along the shores of the White Sea. In five lakes, located near the White Sea Biological Station of Moscow State University, salinity, temperature, pH, concentration of dissolved oxygen, redox potential, and illuminance were measured. Distribution of microorganisms and spectral properties of water layers were also studied. All the lakes had a narrow bright coloured layer in the redox zone caused by mass development of phototropic microorganisms. Light absorption and fluorescence spectra indicated algae containing chlorophyll a predominate in the red water layers while the colouration of green and brown layers is caused by green sulphur bacteria with bacteriochlorophylls d and e. Sunlight is completely absorbed in the redox zone because of the high density of algae and/or bacteria, resulting in aphotic conditions below. Coloured layers act as a specific biotope for special communities of microorganisms. Eukaryotes identified by the 18S rRNA gene included different species of mixotrophic algae and ciliates resistant to anoxia. The water layer colour and spectral characteristics (i.e. light absorption and fluorescence) of water in the redox zone can be considered indicators of the stage of lake isolation from the sea, with the red colour caused by cryptophyte alga Rhodomonas sp. bloom found in earlier stages and brown and green colours caused by green sulphur bacteria in later stages.