Synthesis and characterization of different poly(1‐vinylindole)s for photorefractive materials

The main goal of this research was to verify if some advantages could be obtained by the replacement of poly(1‐vinylcarbazole), a component commonly employed for organic photorefractive materials, with various polymers containing side‐chain heteroaromatic moieties. For this purpose, poly(1‐vinylpyrrole), poly(1‐vinylindole), and some methyl‐substituted compounds of poly(1‐vinylindole) were considered. The best conditions for both monomer synthesis and polymerization were found. A first possible advantage of the new polymeric substrates resided in the values of the glass‐transition temperature, which, as expected, was constantly lower than that of poly(1‐vinylcarbazole). This could lead to a material that requires the introduction of a lower quantity of plasticizer in the final photorefractive blend to display photorefractive behavior at room temperature. In addition, the verified higher electric dipole moments of the pyrrole and indole derivatives could improve the compatibility of the optically nonlinear component required in the system, typically an azo‐molecule, by increasing its solubility inside the blend. All the synthesized vinyl monomers and polymers gave clear spectroscopic evidence of the formation of charge‐transfer complexes with 2,4,7‐trinitrofluorenylidenmalonitrile, an efficient sensitizer for photoconductivity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 253–262, 2001     

Synthesis of poly(p-phenyleneterephthalamide) in presence of polymer matrices

The direct syntheses of poly(p-phenyleneterephthalamide) in presence of poly(vinylpyrrolidone) and poly(4-vinylpyridine) as matrices have been carried out following the so-called Yamazaki's and Higashi's methods. The intrinsic viscosity data of the resulting polyamide were found to be strongly dependent on the matrix used as well as on its molecular weight.     

Easy Separation of Δ and Λ Isomers of Highly Luminescent [IrIII]‐Cyclometalated Complexes Based on Chiral Phenol‐Oxazoline Ancillary Ligands

A new class of neutral cyclometalated iridium(III) complexes with enantiomerically pure C₁‐symmetric phenol‐oxazolines ( 3 a,b ) have been synthetized in high yields and fully characterized. Resolution of the corresponding Δ_R and Λ_R or Δ_S and Λ_S isomers was easily achieved by conventional flash chromatography. The corresponding Δ and Λ helicities have been confirmed by CD spectroscopy and X‐ray crystallography. Regarding the absorption and luminescence properties with unpolarized light, no significant difference between Δ and Λ isomers has been observed. A strong blue luminescence is observed for deaerated solutions of complexes 5 a and 5 b in CH₃CN.     

Pyrene‐Excimers‐Based Antenna Systems

A series of dendrimeric compounds bearing pyrene units were synthesized to afford light‐harvesting antennae based on the formation of intramolecular excimers. The synthetic plan profited from the efficiency of the Huisgen reaction, the 1,3‐dipolar cycloaddition of azides and terminal alkynes, which allowed ready assembly of the different building blocks. The three molecular antennae obtained, of increasing generation, revealed efficient energy transfer both in solution and in the solid state.     

Symmetry generators for null geodesic motion

The concept of conformai dynamical symmetry (CDS) is introduced as a basic tool for the analysis of null geodesic motion. CDSs are characterized as generators of Jacobi fields along null geodesies. Methods for the construction of CDS's based on the connections between CDSs and conformai Killing tensors or on the behavior of CDSs under conformai transformations are then discussed. Finally, a comprehensive analysis of conserved quantities canonically related to CDSs is given.     

Survival analysis in Johnson–Mehl Tessellation

The crystallization process is represented here by a generalized Boolean model, whose parameters are usually unknown. A better understanding of the model may be obtained if we estimate the corresponding parameters. In this paper, we provide non-parametric estimators for the parameters of the model. Among them, the degree of crystallinity at time t is the probability that an arbitrary point in the space has been captured by a crystal before time t. We estimate it following the Kaplan–Meier approach extended to the context of a Johnson–Mehl incomplete tessellation. Three estimators are defined, according to the kind of data we dispose. The results are also illustrated by simulations. We also provide estimators for the parameters describing geometrical aspects of the phenomenon.      

Radial drawings of graphs: Geometric constraints and trade-offs

This paper studies how to compute radially layered drawings of graphs by taking into account additional geometric constraints which correspond to typical aesthetic and semantic requirements for the visualization. The following requirements are considered: vertex centrality, edge crossings, curve complexity, and radial distribution of the vertices. Trade-offs among these requirements are discussed and different linear-time drawing algorithms are presented.     

Efficient universal programmable quantum measurements

A universal programmable detector is a device that can be tuned to perform any desired measurement on a given quantum system, by changing the state of an ancilla. With a finite dimension d for the ancilla only approximate universal programmability is possible, with size d=f(epsilon(-1)) increasing the function of the "accuracy" epsilon(-1). In this Letter we show that, much better than the exponential size known in the literature, one can achieve polynomial size. An explicit example with linear size is also presented. Finally, we show that for covariant measurements exact programmability is feasible.