Photoinduced Coupling of Acetylenes and Quinone in the Solid State as Preorganized Donor−Acceptor Pairs

Crystalline electron donor−acceptor (EDA) complexes of various diarylacetylenes (DA) and dichlorobenzoquinone (DB) are isolated and structurally characterized by X-ray crystallography. Deliberate excitation of either the DB acceptor at λDB = 355 nm or the 1:2 [DA, 2DB] complex at λCT = 532 nm in the solid state leads to [2 + 2] cycloaddition and identical (isomeric) mixtures of the quinone methide products. Time-resolved (ps) diffuse reflectance spectroscopy identifies the ion-radical pair [DA•+, DB•-] as the reactive intermediate derived by photoinduced electron transfer in both photochemical procedures. The effects of crystal-lattice control on the subsequent ion-radical pair dynamics are discussed in comparison with the same photocouplings of acetylenes and quinone previously carried out in solution

Thermal Control of Spin Excitations in the Coupled Ising-Chain Material RbCoCl₃

We have used neutron spectroscopy to investigate the spin dynamics of the quantum (S = 1/2) antiferromagnetic Ising chains in RbCoCl3. The structure and magnetic interactions in this material conspire to produce two magnetic phase transitions at low temperatures, presenting an ideal opportunity for thermal control of the chain environment. The high-resolution spectra we measure of two-domain-wall excitations therefore characterize precisely both the continuum response of isolated chains and the "Zeeman-ladder" bound states of chains in three different effective staggered fields in one and the same material. We apply an extended Matsubara formalism to obtain a quantitative description of the entire dataset, Monte Carlo simulations to interpret the magnetic order, and finite-temperature density-matrix renormalization-group calculations to fit the spectral features of all three phases

Incidências de manifestações patológicas causadas por construções nas edificações vizinhas no município de Vitória - ES

O crescimento populacional das cidades resulta no uso e ocupação intensiva do espaço urbano, provocando dessa forma grandes adensamentos. No período de construção ou reforma de edificações, principalmente obras de múltiplos andares, acontecem reclamações dos proprietários de edificações, que se sentem atingidos por efeitos de obra vizinha. Essas ocorrências podem se transformar em manifestações patológicas nas edificações circunvizinhas pré-existentes. O presente trabalho tem o objetivo de detectar a incidência de danos e de manifestações patológicas através de uma pesquisa de casos com laudos de vistorias oficiais registradas no município de Vitória ES, bem como a realização de estudo qualitativo e quantitativo das patologias manifestadas nessas edificações, decorrentes de construções circunvizinhas. Caracteriza-se como pesquisa documental tendo o método da incidência como metodologia. Os resultados apresentados foram: quatro bairros, Jardim da Penha, Jardim Camburi, Praia do Canto e Santa Luiza, somam 56,67% do total de casos pesquisados; o ano com maior número de laudos foi 2007; da natureza das edificações afetadas, 49,09% são unifamiliares; da natureza das obras causadoras, 58,55% são edificações multifamiliares; da legalidade das obras causadoras, 66,66% foram licenciadas junto a Prefeitura; quanto ao tipo de manifestação patológica, verificou-se a presença de fissuras em 47,97% dos casos pesquisados; das patologias pesquisadas, 68,46% surgiram no período de fundação; a fase da fundação que gerou maior incidência de patologias foi o período de cravação de estacas, com 31,57% dos casos. Conclui-se que as legislações, devem ser aperfeiçoadas para prevenir ou até mesmo, num primeiro momento, minimizar estas ocorrências

Stereodifferentiation in the formation and decay of the encounter complex in bimolecular electron transfer with photoactivated acceptors

Experimental evidence has been obtained for the involvement of encounter complexes between both enantiomers of a π,π* triplet excited ketone and a chiral phenol or indole. Determination of the pre-equilibrium constants (KEC) and the intrinsic decay rate constants (kd) indicates a significant stereodifferentiation in both steps of the quenching process.Perez Prieto, Julia, [email protected] ; Galian, Raquel Eugenia, [email protected] ; Morant Miñana, Maria Carmen, [email protected]

Versatile Coordination of Cyclopentadienyl-Arene Ligands and Its Role in Titanium-Catalyzed Ethylene Trimerization

Cationic titanium(IV) complexes with ansa-(η5-cyclopentadienyl,η6-arene) ligands were synthesized and characterized by X-ray crystallography. The strength of the metal-arene interaction in these systems was studied by variable-temperature NMR spectroscopy. Complexes with a C1 bridge between the cyclopentadienyl and arene moieties feature hemilabile coordination behavior of the ligand and consequently are active ethylene trimerization catalysts. Reaction of the titanium(IV) dimethyl cations with CO results in conversion to the analogous cationic titanium(II) dicarbonyl species. Metal-to-ligand backdonation in these formally low-valent complexes gives rise to a strongly bonded, partially reduced arene moiety. In contrast to the η6-arene coordination mode observed for titanium, the more electron-rich vanadium(V) cations [cyclopentadienyl-arene]V(NiPr2)(NC6H4-4-Me)+ feature η1-arene binding, as determined by a crystallographic study. The three different metal-arene coordination modes that we experimentally observed model intermediates in the cycle for titanium-catalyzed ethylene trimerization. The nature of the metal-arene interaction in these systems was studied by DFT calculations.

Triplet exciplexes as energy transfer photosensitisers

Experimental evidence is provided for the occurrence of triplet–triplet energy transfer from benzoylthiophene–indole exciplexes to naphthalenes with a remarkable stereodifferentiation; chiral recognition is also observed in the decay of the generated naphthalene triplets.Perez Prieto, Julia, [email protected] ; Galian, Raquel Eugenia, [email protected] ; Morant Miñana, Maria Carmen, [email protected]