Characterization of the Electronic Excited-State Energetics and Solution Structure of Lanthanide(III) Complexes with the Polypyridine Ligand 6,6\u27-Bis[bis(2-pyridylmethyl)aminomethyl]-2,2\u27-bipyridine

Absorption, emission, and excitation spectra for solid-state and solution of Tb(III), Dy(III), and Gd(III) complexes with the polypyridine ligand 6,6‘-bis[bis(2-pyridylmethyl)-aminomethyl]-2,2‘-bipyridine (C36H34N8) are presented. Measurements of excited-state lifetimes and quantum yields in various solvents at room temperature and 77 K are also reported and used to characterize the excited-state energetics of this system. Special attention is given to the characterization of metal-to-ligand energy transfer efficiency and mechanisms. The measurement of circularly polarized luminescence (CPL) from the solution of the Dy(III) complex following circularly polarized excitation confirms the chiral structure of the complexes under study. No CPL is present in the luminescence from the Eu(III) or Tb(III) complex because of efficient racemization. The variation of the magnitude of the CPL as a function of temperature from an aqueous solution of DyL is used for the first time to characterize the solution equilibria between different chiral species

Investigations of the spectral properties of lanthanide(III) complexes with 3,3′-bi-isoquinoline-2,2′-dioxide (biqO \u3c inf\u3e 2 ) and a biqO \u3c inf\u3e 2 -cryptate in solution, solids, and gels

Increasing interest has been observed in the spectroscopic properties of lanthanide ions in cryptates and heteroaromatic ligands where the lanthanide ions are encapsulated into the ligand structure [B. Alphov, J.M. Lehn, G. Matkis, Angen. Chem. 99 (1987) 259; J.M. Lehn, in: V. Balzani (Ed.), Supramolecular Photochemistry, Reidel, Dordrecht, 1987, pp. 29-42; N. Sabbatini, S. Perathoner, V. Balzani, B. Alpha, J.M. Lehn, in: V. Balzani (Ed.), Supramolecular Photochemistry, Reidel, Dordrecht, 1987, pp. 187-206]. Of special interest are those cryptates and chelating ligands in which efficient energy transfer between the ligands and the rare-earth ion takes place. The goal of the present studies is the description of the best conditions for this intra-system energy transfer in two types of compounds with 3,3′-biisoquinoline-2,2′-dioxide (biqO2), and for a cryptate incorporating biqO2. Results are reported for these complexes prepared in water and non-aqueous solutions, and in gels obtained by different methods. Spectroscopic methods, including absorption, emission and excitation spectra, at 293 and 77 K were used to characterize the type and symmetry of the complexes formed in solutions and gels under different conditions (pH and concentration). It is demonstrated that the type of solvent used in the sol-gel process affects the emission intensity through perturbation of the ligand:metal electronic energy levels, and the symmetry and stability of the complexes. Correlation of the solid state spectroscopic results with those in solution and gel for Eu(III) ions, illustrates the role of the energy back transfer process in emission quenching. This is found to be temperature dependent

Preparation and Spectroscopy of Lanthanide Single Crystals with Isoleucine

Single crystals of lanthanide complexes (Ln = Pr, Nd, Eu) were obtained from aqueous solutions. Optical properties of the title compound are investigated by absorption, excitation, and emission spectra. Probabilities of electronic transitions were analysed and participation of vibronic components in the spectra were found. Temperature effect on the spectra was studied and analysed in terms of cooperative interaction

Optical Properties of Europium Compounds with L- and DL-α-Alanine-Hydroxamic Acids

Two of europium complexes with L- and DL-α-alanine-hydroxamic acids were synthesized. To our knowledge they are the first examples of X-ray and spectral data of lanthanide single crystals with hydroxamic acid derivatives. Both compounds consist of dimers in their structures, formed by two OH bridging groups of amino-hydroxamic acid molecules. Besides, two metal ions are chelated by CO and OH groups, forming five-membered rings. In the complex with L-ligand, different than in the DL-one, two additional perchloric acid molecules are included in crystal cavities and form hydrogen bondings with nitrogen and oxygen atoms of the ligand. Absorption, emission and excitation spectra were measured and analyzed at room and low temperatures. Structural effect of ligand chirality was found and its spectroscopic consequences are reported. The effect of the dimeric structure on spectroscopic properties is discussed

Thinking deep. Acting on top. underground built heritage and its fringe as a community catalyst for local sustainable development: Exploratory cases from poland and greece

Underground Built Heritage (UBH) is a distinct class of cultural heritage providing a focal point for community pride and engagement to become a springboard for local sustainable development (LSD). This research aims to articulate how local UBH and its fringe serve as a facilitator of communal identity to mobilize community care towards social and economic development with less involvement from the state and the market actors. For this purpose, local (and less-conspicuous) cases of UBH are employed in Warsaw, Poland, and Volos, Greece, indicating the power of UBH to connect and engage local communities with places, triggering a momentum for a truly bottom-up action that pays less attention to market considerations and state support. The studied UBH sites have been discussed according to an established common framework, dealing with five main issues: (a) general context and status, (b) history, (c) users and management, (d) ecosystem services, and (e) introduction of the paradigm of living labs. The analysis was based on a thorough literature review and complemented by field observations and interviews. The results provide evidence for UBH as a potential facilitator of social and economic development. The case studies in Poland and Greece showed that local actors were involved in activities and social networks of tacit knowledge, generating community building to reinforce bottom-up activities in contact with UBH. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

The measurement of circularly polarized luminescence from racemic lanthanide complexes prepared in sol-gels

Circularly polarized luminescence (CPL) has been measured from rigid sol-gels containing racemic D3 complexes of Eu(III) with 2,6-pyridine-dicarboxylate (DPA) and oxydiacetate (ODA). These complexes occur in solution and sol-gels as racemic mixtures. CPL was generated from the racemic mixture by preparing a non-racemic excited state through circularly polarized excitation. The CPL measured from the sol-gel containing Eu(DPA)33- is significantly less from that measured in solution. This result is interpreted in terms of the effects of concentration depolarization. © 2000 Elsevier Science S.A. All rights reserved