Tuning the overall emission quantum yield (ϕLLn), dissymmetry factor (g_lum), as well as CPL brightness by changing the electronic structure and microsymmetry of the Eu^III coordination polyhedron.

Leishmaniasis is a highly prevalent, yet neglected disease caused by protozoan parasites of the genus Leishmania. In the search for newer, safer, and more effective antileishmanial compounds, we herein present a study of the mode of action in addition to a detailed structural and biological characterization of LQOF-G6 [N-benzoyl-N′-benzyl-N″-(4-tertbutylphenyl)guanidine]. X-ray crystallography and extensive NMR experiments revealed that LQOF-G6 nearly exclusively adopts the Z conformation stabilized by an intramolecular hydrogen bond. The investigated guanidine showed selective inhibitory activity on Leishmania major cysteine protease LmCPB2.8ΔCTE (CPB) with ~73% inhibition and an IC_50-CPB of 6.0 µM. This compound did not show any activity against the mammalian homologues cathepsin L and B. LQOF-G6 has been found to be nontoxic toward both organs and several cell lines, and no signs of hepatotoxicity or nephrotoxicity were observed from the analysis of biochemical clinical plasma markers in the treated mice. Docking simulations and experimental NMR measurements showed a clear contribution of the conformational parameters to the strength of the binding in the active site of the enzyme, and thus fit the differences in the inhibition values of LQOF-G6 compared to the other guanidines. Furthermore, the resulting data render LQOF-G6 suitable for further development as an antileishmanial drug.

Temperature measurements are crucial in numerous industries, spurring ongoing innovations in sensing technology. Among the myriad techniques being explored, luminescence thermometry using lanthanide(III) (Lnⁱⁱⁱ) coordination polymers has garnered considerable interest. However, there remains a scarcity of mapping design strategies for optimizing luminescent temperature probes. To address this issue, theoretical models that examine photophysical dynamics can offer valuable insights into the thermal response of luminescence. In this work, we show a detailed study that integrates theoretical modelling with experimental analysis of the thermal dependence of luminescence in two coordination polymers: [Ln(tfa)₃(μ-dppeo)]_n (1) and [Ln(tfa)₃(μ-dppbo)]_n (2) (Ln = Eu and Tb, tfa⁻ = trifluoroacetylacetonate, and the bridge ligands are [(diphenylphosphoryl)R](diphenyl)phosphine oxide, R = ethyl − dppeo − or butyl − dppbo). By combining experimental and theoretical methods, the mechanisms governing intramolecular and intermolecular energy transfer are investigated. The thermal behaviours of ligand-to-Ln^III and Ln^III-to-Ln^III energy transfer processes are dissected upon direct ligand or Tb^III excitation, shedding light on their contributions to luminescence thermometry and enabling control of the thermal response. Additionally, we adapted and experimentally validated a theoretical protocol for mapping temperature sensing based on the population dynamics of emitting states, demonstrating its feasibility for designing molecular thermometers with enhanced sensitivity. Overall, this study sets the stage for unfolding thermal response mechanisms across multiple excitation channels, offering a foundation for the development of luminescent temperature probes.

Understanding the dynamics of photophysical processes in Ln³⁺ complexes remains challenging due to the intricate nature involving the metallic center, where sensitization (antenna effect) plays a pivotal role. Current studies have often overlooked the vibronic coupling within the antenna effect, leading to incomplete insights into excited-state dynamics. To address these shortcomings, we introduce a novel theoretical and computational approach that leverages the impact of the vibrational modes of the S₁ and T₁ states in this effect through the correlation function formalism, offering a comprehensive view of intersystem crossing (ISC). Our approach achieves a desirable alignment between empirical and theoretical rates, outperforming previously employed semiclassical methods. A groundbreaking finding is that vibronic coupling with vibrations in the 700-1600 cm^-1 energy range is crucial for higher ISC, and local vibrational mode analysis identified that this process is driven by delocalized vibrations across the molecule. These results shed light on the key molecular fragments responsible for vibronic coupling, opening an avenue for harnessing faster ISC by tailoring the ligand scaffold. Overall, it also demonstrates how ISC dynamics can serve as a bridge between theory and experiment, furnishing detailed mechanistic insights and a roadmap for the development of brighter compounds.

The elucidation of the mechanisms governing the photophysical properties of trivalent lanthanide (LnIII) complexes embedded in polymeric matrices, such as poly­(methyl) methacrylate (PMMA) and polyvinylidene fluoride (PVDF), is challenging due to their intricate composite nature. Although theoretical modeling offers insights into film luminescence, conventional computational strategies face significant limitations. Given the large-scale nature of these systems, which encompass thousands of atoms, full-scale quantum mechanical (QM) simulations are impractical. Existing methodologies often integrate molecular mechanics (MM) with QM, yet such hybrid frameworks introduce inaccuracies in excited-state calculations. To address these challenges, this study proposes a multilevel computational protocol employing a hybrid QM/QM approach. Density functional theory (DFT) was used for the [Eu­(dbm)4]− complex (dbm = 1,3-diphenyl-1,3-propanedione), while the polymeric environment was treated using the GFNn-xTB method. The protocol demonstrated strong agreement between experimental and theoretical emission quantum yields (QY) for both the isolated complex and [Eu­(dbm)4]−/PMMA or PVDF films. Our findings revealed that angular and length distortions in the Eu–O bonds within PVDF were induced by increased packing around the complex, impacting the ligand-EuIII energy transfer by elevating the triplet state energy. These results underscore the predictive capabilities of the hybrid QM/QM strategy, offering a robust alternative for deciphering opto-structural relationships in LnIII-based polymeric films.

Evaluating opto-structural correlations to tailor the luminescence of polymeric films based on Eu ^III -doped phosphors using a new combined spectroscopic and theoretical protocol.