Ana Matos Beja

Novel erbium(III) fluorinated β-diketonate complexes with N,N-donors for optoelectronics: from synthesis to solution-processed devices

Three novel ternary Er3+ complexes emitting in the C band transmission window for fiber optic communications have been synthesised and their structures have been elucidated by single crystal X-ray diffraction. The fluorinated β-diketonate ligand, 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione, combines a good absorption cross-section in the ultraviolet region with reduction of non-radiative quenching of the Er3+ emission, while the rigidity and bulkiness of the three different N,N-donors (2,2′-bipyridine, bathophenanthroline and 5-nitro-1,10-phenanthroline) have a pronounced impact on the emission intensity of luminescence. Furthermore, the choice of the ancillary ligand also determines the efficiency of the antenna effect, leading to complete quenching of the ligand-associated visible emission for the optimized complex with 5-nitro-1,10-phenanthroline. Solution processed 1.54 μm organic light-emitting diodes have been manufactured and characterized for this complex, confirming the aforementioned complete resonant energy transfer from the ligands to the Er3+ ion. The features of the reported device fabrication show a simple way to obtain large area NIR-OLEDs.

Study of the suitability of silica based xerogels synthesized using ethyltrimethoxysilane and/or methyltrimethoxysilane precursors for aerospace applications

Silica based materials were synthesized using ethyltrimethoxysilane (ETMS) and/or methyltrimethoxysilane (MTMS) precursors by sol–gel technology, in order to ascertain if their properties are suitable for aerospace applications. When ETMS was used alone and in equimolar ETMS/MTMS mixtures, no gel formation took place and a resin-like precipitate was observed. After drying, a compact tablet was formed. When mixtures of 25% ETMS/75% MTMS and MTMS alone were used, gel formation occurred and xerogels were produced upon drying. Chemical and structural characterization of the obtained materials was performed using Elemental Analysis, FTIR, XRD and SEM. Bulk density, specific surface area, contact angle and the thermal behavior were also evaluated. For materials from ETMS, the chemical structure grows preferentially in one direction and, in the case of MTMS the growth follows a 3D pattern. The use of ETMS precursor leads to a significant increase in the product density, accompanied by a decrease in the specific surface area. It also leads to a decrease in the thermal stability limit of the synthesized materials. Then, ETMS precursor is less appropriate than MTMS precursor for space applications. However, ETMS co-precursor in mixtures with MTMS contributes to the increase in the hydrophobic character of the synthesized materials.

Diastereoselective hydroformylation of Δ4-steroids with rhodium–phosphite catalysts

Abstract The hydroformylation of two steroidal substrates, namely 17β-acetoxyandrost-4-ene 1 and 3β,17β-diacetoxyandrost-4-ene 2, with a rhodium tris(O-tert-butylphenyl)phosphite catalyst was investigated. In both cases, the major reaction product was 4β-formyl-17β-acetoxy-5β-androstane 3, which was isolated and characterized by X-ray diffraction and NMR techniques. This reaction is the first example of catalytic carbonylation to the β face of a steroid backbone. The effect of reaction temperature, the pressure at which the reaction was completed and the ligand:Rh ratio on the regio- and stereoselectivity of the reaction is also discussed.

Cycloaddition reactions of 3-aryl-5-phenyl-5H, 7H-thiazolo[3,4-c]oxazol-4-ium-1-olates

Intermolecular 1,3-dipolar cycloaddition of (5R)- and (5S)-3,5-diphenyl-5H,7H-thiazolo[3,4-c]oxazol-4-ium-1-olates, (5R)- and (5S)-3-(p-methoxyphenyl)-5-phenyl-5H,7H-thiazolo-[3,4-c]oxazol-4-ium-1-olates with a range of dipolarophiles is described. New chiral 5-aryl-3-phenyl-1H,3H-pyrrolo[1,2-c]thiazoles with R and S configuration were obtained. The structure of methyl (3R)-3-phenyl-5-(p-methoxyphenyl)-1H,3H-pyrrolo[1,2-c]thiazole-6-carboxylate was determined by X-ray crystallography. The synthesis of 7,7a-dihydro-1H,3H-pyrrolo[1,2-c]thiazole-6,7-dicarboxylates was also achieved.

Strong hydrogen-bonded amino acid dimers in l-alanine alaninium nitrate

The title compound, C3H7NO2*C3H8NO2+*NO3-, contains L-alanine-alaninium dimers bonded via the carboxyl groups by a strong asymmetric hydrogen bond with an O...O distance of 2.4547 (19) A. The neutral alanine molecule exists as a zwitterion, where the carboxyl group is dissociated and the amino group is protonated. The alaninium cation has both groups in their acidic form. The alanine molecule and the alaninium cation differ only slightly in their conformation, having an N-C(alpha)-C=O torsion angle close to -25 degrees. The dimers and the nitrate anion are joined through a three-dimensional hydrogen-bond network, in which the full hydrogen-bonding capabilities of the amino groups of the two alanine moieties are realised.

Intermolecular Dipolar Cycloaddition Reactions of 5H,7H-Thiazolo[3,4-c]oxazol-4-ium-1-olates

Abstract (5R)-3-Methyl-5-phenyl-5H,7H-thiazolo[3,4-c]oxazol-4-ium-1-olate was generated in the presence of a range of dipolarophiles. The intermolecular 1,3-dipolar cycloaddition of this mesoionic species led to the synthesis of chiral 1H-pyrrolo[1,2-c]thiazole derivatives 7a, 7b, 8, 14, 18, 19 and 20. In the reaction with methyl and ethyl vinyl ketone, spiro compounds 9 and 15 were also obtained. The structure of compound 15 was determined by X-ray crystallography.

Crystal structure of hydrated diphenylguanidinium hexafluoroferrate (III)

Abstract The crystal structure of 3C13H14N3+FeF63−·3.5H2O was determined. Both phenyl rings of the diphenylguanidine cation are oriented syn to the central CNH2 group. The anions and cations are held together by a three-dimensional network of hydrogen bonds. In the synthesis of this compound, a second phase (iron trifluoride trihydrate) was formed and identified by powder diffraction data. Mossbauer results show two different iron environments compatible with the two phases reported.

The reaction of azoles with 17-chloro-16-formylandrosta-5,16-dien-3β-yl-acetate: Synthesis and structural elucidation of novel 16-azolylmethylene-17-oxoandrostanes

The synthesis and structural elucidation, by 1D and 2D NMR and X-ray diffraction techniques, of novel E/Z 16-azolylmethylene-17-oxoandrostanes 2-9 prepared from the Vilsmeier-Hack reaction product 17-chloro-16-formylandrosta-5,16-dien-3β-yl acetate 1 is reported. The reaction proceeds with pyrrole and pyrrole-alike nitrogen heterocycles such as 7-azaindole, indole, and 3-methylindole, in DMF, at 80°C, in the presence of K(2)CO(3), and allowed the attachment of privileged heterocyclic moieties, through the nitrogen atom to the steroid core at C16 via a methine carbon bridge, which is unprecedented in the literature and of potential synthetic and biological interest. Considerations on the possible reaction mechanism are included. All the synthesized compounds are new and are currently being tested for biological activities.

Ethyl 4-do­decyl-3,5-di­methyl-1H-pyrrole-2-carboxyl­ate: intermolecular interactions in an amphiphilic pyrrole

The title compound, C(21)H(37)NO(2), is a new amphiphilic pyrrole with a long hydrocarbon chain, which will be used as a precursor for the synthesis of Langmuir-Blodgett films of porphyrins. Molecules related by an inversion centre are joined head-to-head into dimers by strong N-H.O hydrogen bonds. The dimers pack in the structure with their carbon chains parallel to one another, thereby forming alternating layers of carbon chains and pyrrole heads. The structure is further stabilized by two weak C-H.pi intermolecular interactions, thereby saturating the hydrogen-bonding capability of the aromatic pi-electron clouds.

Contribution to the synthesis of chiral allenic esters

A phosphorus ylide bearing a 10-phenylsulfonylisoborneol unit reacted with ketenes, generated in situ from acid chlorides and triethylamine, to give allenic compounds. The reaction with methylketene led to asymmetric induction with the selective synthesis of an allene with axial chirality corresponding to an S configuration. The structure of the chiral allene 10-phenylsulfonylisobornyl penta-2,3-dienoate was determined by X-ray crystallography. Chirooptical studies of the chiral allene derivatives were done.