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

Structure and photoluminescent features of di-amide cross-linked alkylene-siloxane hybrids

Novel amide cross-linked alkylene/siloxane hybrid materials (di-amidosils) synthesized by the sol-gel process have been investigated. Two samples identified by the notation d-A(x) with x = 4 and 8 (where x is the number of methylene groups of the alkylene chain) have been produced as transparent, amorphous, rigid monoliths, thermally stable up to about 381 and 400 ºC, respectively. In the d-A(8) hybrid the siliceous framework is composed of [(SiO)3Si(CH2)-] and [(SiO)2(HO)Si(CH2)-] substructures. Structural unit distances of 4.1 and 4.2 Å and average interparticle distances of 12 and 17 Å have been determined for d-A(4) and d-A(8), respectively. In these compounds the alkyl chains are disordered and adopt gauche conformations. While a negligible proportion of the amide linkages remain non-bonded, the great majority of these groups belong to highly disordered strong hydrogen-bonded amide-amide associations. The hybrids introduced are room temperature white light emitters, presenting an emission large, broad band in the blue/purplish-blue spectral region. The origin of such band have been ascribed to the convolution of donor-acceptor pair (D-A) recombinations that occur in the NH groups of the urea linkages and in the siliceous nanodomains. The maximum quantum yield value of the d-A(8) di-amidosil is 5.4 %.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/P/CTM/46780/03; SFRH/BD/13559/03

Structure and Spectroscopy of Selected Lanthanide Compounds with Coordination Number from 9 to 6

The lecture deals with a group of lanthanide compounds in which some structural factors influence, in a special way, spectroscopic properties of the systems under investigation. The following systems were chosen: three with polymeric structure, two of the dimer type, one a pseudo-dimer system with coordination number (C.N.) = 7, and an octahedral compound of LnL$\text{}_{6}$ type. The crystal structures of the systems under consideration will be shown, their absorption and excitation spectra will be presented and confronted with X-ray data. Radiative and nonradiative processes will be considered and the role of cooperative interactions analyzed. Some aspects of dynamics in solids will be done, too

Spectroscopic Properties of Neodymium Perchlorates in 2-Halogeno Derivatives of Ethanol. Part II

The spectroscopic studies of anhydrous neodymium perchlorate in two series of 2-halogeno derivatives of ethyl alcohol are presented. The changes of intensities of $\text{}^{4}$I$\text{}_{9}\text{}_{/}\text{}_{2}$ → $\text{}^{2}$G$\text{}_{7}\text{}_{/}\text{}_{2}$, $\text{}^{4}$G$\text{}_{5}\text{}_{/}\text{}_{2}$ hypersensitive transitions are discussed within the framework of Mason's polarizability mechanism. Anomalous dependence of band intensities was found for the 2-fluoro derivatives. The linear relation of oscillator strength vs. solvent polarizability was broken for the 2-bromine and 2-iodine derivatives of ethyl alcohol. The effort was made for explanation of such strange results