A new strategy for the easy polymerization of anionic [Ln(Q^cy)₄]⁻ (HQ^cy-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) into two-dimensional layers of [AgLn(Q^cy)₄]_n (Ln = Sm, Eu, Gd, Tb and Dy) is proposed by binding the single molecular anions [Ln(Q^cy)₄]⁻ to silver cations through the coordination of the pyridinic nitrogen atoms of the pyrazolonate rings. The luminescent properties of [AgLn(Q^cy)₄]_n have been studied in detail, and it was shown that the previously described low photoluminescence quantum yield (PLQY) of [Eu(Q^cy)₄]⁻ is due to Ligand-To-Metal Charge Transfer (LMCT) quenching, which is effectively suppressed in the heterometallic [AgEu(Q^cy)₄]_n polymer. Sensibilization coefficients for H₃O[Eu(Q^cy)₄], [AgEu(Q^cy)₄]_n, and H₃O[Sm(Q^cy)₄] complexes (n ≈ 1) were estimated via theoretical analysis (also by using Judd-Ofelt theory for Sm³⁺) and PLQY measurements.

The impact of substituents at the 4- and 7-positions of 1,10-phenanthroline-2,9-dicarboxamides on the photophysical properties of the ligands and their coordination compounds with the lanthanide triad—europium, gadolinium, and terbium—was analyzed. This study demonstrates how modification of the electronic nature of ligands through the incorporation of diverse functional groups affects the luminescence properties of their complexes. The introduction of various substituents leads to the appearance of intra-ligand or ligand-to-ligand charge transfer (CT) states. The highest luminescence efficiency was observed for LH·Eu(NO₃)₃ (Q_in = 54.1% and Q_L = 9.6%), suggesting strong luminescence quenching of the CT state. It was found that a relatively low ΔE (∼3000 cm⁻¹) supports direct energy transfer from S₁ to T₁ bypassing the CT state, even though it is outside Reinhoudt's optimal range. The introduction of fluorines leads to the strongest luminescence quenching among all the substituents.

The influence of the degree of π-conjugation in biaroylmethane ligands upon Eu³⁺ luminescence efficiency in corresponding neutral tris-complexes was investigated in depth. The data obtained by both steady-state and time-resolved luminescence measurements gave an inside into electronic energy transfer mechanisms in the abovementioned complexes. It was shown that extension of the π-system in the naphthalene moiety in comparison to the phenyl one lead to a substantial decrease of both the S₁ and T₁ energy of the corresponding symmetrical β-diketones, which, in turn, led to a decrease of the total quantum yield of respective Eu³⁺ complexes. The obtained results are of interest for the rational design of highly luminescent complexes with NIR-emitting lanthanides, as the resonant levels energies are low and can hardly be sensitized by common ligands.

The first Yb complexes comprising a quinoline-2-carboxylate (quinaldinate, Q⁻) ligand, namely 1D-polymeric [Yb(acac)₂(Q)]_n (1, acac⁻ is the acetylacetonate (pentane-2,4-dionate) anion) and mononuclear [Yb(acac)₂(Q)(Phen)] (2, Phen is 1,10-phenanthroline), are reported. The bifunctionality of both complexes as field-induced single-molecule magnets (SMMs) and near IR luminophores has been revealed. The SMM properties of 1 and 2 have been discussed in terms of the geometry and composition of the coordination environment. Also, 1 is the first example of 1D-polymeric SMMs with the capped octahedral surrounding of Yb³⁺. The photoluminescence quantum yields (PLQYs) of 1 and 2 are 2 and 4%, respectively. The origins of this difference are discussed. Surprisingly, the PLQY value of 2 is high for compounds comprising a lot of C–H vibrational quenchers, being the highest one for reliably characterized Yb β-diketonate complexes, and surpassing those for complexes with a broad range of anionic ligands. In this respect, the role of the Phen ligand is to tune the coordination mode of Q⁻ thereby decreasing the energy of coordinating C–O oscillators rather than to act as a typical antenna ligand. These results can give rise to an alternative route to elaborate efficient Yb-based luminophores via the substitution of the β-diketonate ligands controlled by the introduction of appropriate neutral ligands.

Heteroleptic Zn₂Gd₂ and Zn₂Eu₂ complexes have been synthesized and their photophisical properties have been investigated. The complexes demonstrate antibacterial activity and cytotoxic effect on the cancer cells higher than on healthy fibroblasts.

Six new complexes of the ligand HQ^cy (-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) and Ln³⁺ ions with emission in the near-infrared (Nd³⁺) or visible and near-infrared (Sm³⁺, Pr³⁺) spectral regions were synthesized and characterized using various methods, including single crystal X-ray diffraction. The study demonstrated that both tris complexes [LnQ^cy₃(H₂O)(EtOH)] and tetrakis-acids [H₃O][LnQ^cy₄] can be synthesized by varying the synthetic conditions. The photochemical properties of the complexes were investigated experimentally and theoretically using various molecular spectroscopy techniques and Judd–Ofelt theory. The objective was to quantitatively and qualitatively disclose the influence of complex stoichiometry on its luminescence properties. The study showed that the addition of an extra ligand molecule (in the tetrakis species) increased molar extinction by up to 2 times, affected the shape of photoluminescence spectra, especially of the Pr³⁺ complex, and increased the quantum yield of the Sm³⁺ complex by up to 2 times. The results obtained from this study provide insights into the luminescent properties of lanthanide coordination compounds, which are crucial for the design and development of novel photonic materials with tailored photophysical properties.