Tris(pentafluoroethyl)silanol Derivatives and the Lewis Amphoteric Tris(pentafluoroethyl)silanolate Anion, [Si(C2F5)3O]−

While alkyl-substituted siloxanes are widely known, virtually nothing is known about perfluoroalkyl siloxanes and their congener species, the silanols and silanolates. We recently reported on the tris(pentafluoroethyl)silanide ion, [Si(C₂F₅)₃]⁻, which features Lewis amphoteric character deriving from the pentafluoroethyl substituents and their strong electron-withdrawing properties. Transferring this knowledge, we investigated the Lewis amphoteric behavior of the tris(pentafluoroethyl)silanolate, [Si(C₂F₅)₃O]⁻. In order to examine such Lewis amphoteric behavior, we first developed a strategy for the synthesis of the corresponding silanol Si(C₂F₅)₃OH, which readily condenses at room temperature to the hexakis(pentafluoroethyl)disiloxane, (C₂F₅)₃SiOSi(C₂F₅)₃. Deprotonation of Si(C₂F₅)₃OH employing a sterically demanding phosphazene base allows the characterization of the first example of a dimeric triorganosilanolate: the dianionic hexakis(pentafluoroethyl)disilanolate, [{Si(C₂F₅)₃O}₂]²⁻, implies Lewis amphoteric character of the monomeric [Si(C₂F₅)₃O]⁻ anion.     

Synthesis of New Chlorin e6 Trimethyl and Protoporphyrin IX Dimethyl Ester Derivatives and Their Photophysical and Electrochemical Characterizations

In view of increasing demands for efficient photosensitizers for photodynamic therapy (PDT), we herein report the synthesis and photophysical characterizations of new chlorin e₆ trimethyl ester and protoporphyrin IX dimethyl ester dyads as free bases and Zn^II complexes. The synthesis of these molecules linked at the β‐pyrrolic positions to pyrano[3,2‐c]coumarin, pyrano[3,2‐c]quinolinone, and pyrano[3,2‐c]naphthoquinone moieties was performed by using the domino Knoevenagel hetero Diels–Alder reaction. The α‐methylenechromanes, α‐methylenequinoline, and ortho‐quinone methides were generated in situ from a Knoevenagel reaction of 4‐hydroxycoumarin, 4‐hydroxy‐6‐methylcoumarin, 4‐hydroxy‐N‐methylquinolinone, and 2‐hydroxy‐1,4‐naphthoquinone, respectively, with paraformaldehyde in dioxane. All the dyads as free bases and as Zn^II complexes were obtained in high yields. All new compounds were fully characterized by 1D and 2D NMR techniques, UV/Vis spectroscopy, and HRMS. Their photophysical properties were evaluated by measuring the fluorescence quantum yield, the singlet oxygen quantum yield by luminescence detection, and also the triplet lifetimes were correlated by flash photolysis and intersystem crossing (ISC) rates. The fluorescence lifetimes were measured by a time‐correlated single photon count (TCSPC) method, fluorescence decay associated spectra (FDAS), and anisotropy measurements. Magnetic circular dichroism (MCD) and circular dichroism (CD) spectra were recorded for one Zn^II complex in order to obtain information, respectively, on the electronic and conformational states, and interpretation of these spectra was enhanced by molecular orbital (MO) calculations. Electrochemical studies of the Zn^II complexes were also carried out to gain insights into their behavior for such applications.     

Mechanism of Host–Guest Complex Formation and Identification of Intermediates through NMR Titration and Diffusion NMR Spectroscopy

The formation of host–guest (H‐G) complexes between 1,8‐bis[(diethylgallanyl)ethynyl]anthracene (H) and the N‐heterocycles pyridine and pyrimidine (G) was studied in solution using a combination of NMR titration and diffusion NMR experiments. For the latter, diffusion coefficients of potential host–guest structures in solution were compared with those of tailor‐made reference compounds of similar shape (synthesized and characterized by NMR, HRMS, and in part XRD). Highly dynamic behavior was observed in both cases, but with different host–guest species and equilibria. With increasing concentrations of the pyridine guest, the equilibrium H₂?H₂κ¹‐G₁?HG₂ is observed (in the second step a host dimer coordinates one guest molecule); for pyrimidine the equilibrium H₂→H₁κ²‐G₁?HG₂ is observed (the formation of a 1:1 aggregate is the second step).     

Some remarks on compact constant mean curvature hypersurfaces in a halfspace of ℍ n+1

We consider embedded compact hypersurfacesM in a halfspace of hyperbolic space with boundaryM in the boundary geodesic hyperplaneP of the halfspace and with non-zero constant mean curvature. We prove the following. Let {M _n } be a sequence of such hypersurfaces withM _n contained in a disk of radiusr _n centered at a point P such thatr _n 0 and that eachM _n is a large. H-hypersurface,H > 1. Then there exists a subsequence of {M _n } converging to the sphere of mean curvatureH tangent toP at. In the case of smallH-hypersurfaces orH 1, if we add a condition on the curvature of the boundary, there exists a subsequence of {M _n } which are graphs. The convergence is smooth on compact subset of ³ .     

Intra-organizational Networks and Performance: A Review

Intra-organizational network research had its first heyday during the empirical revolution in social sciences before World War II when it discovered the informal group within the formal organization. These studies comment on the classic sociological idea of bureaucracy being the optimal organization. Later relational interest within organizational studies gave way to comparative studies on the quantifiable formal features of organizations. There has been a resurgence in intra-organizational networks studies recently as the conviction grows that they are critical to organizational and individual performance. Along with methodological improvements, the theoretical emphasis has shifted from networks as a constraining force to a conceptualization that sees them as providing opportunities and finally, as social capital. Because of this shift it has become necessary not only to explain the differences between networks but also their outcomes, that is, their performance. It also implies that internal and external networks should no longer be treated separately.Research on differences between intra-organizational networks centers on the influence of the formal organization, organizational demography, technology and environment. Studies on outcomes deal with diffusion and adaptation of innovation; the utilization of human capital; recruitment, absenteeism and turnover; work stress and job satisfaction; equity; power; information efficiency; collective decision making; mobilization for and outcomes of conflicts; social control; profit and survival of firms and individual performance.Of all the difficulties that are associated with intra-organizational network research, problems of access to organizations and incomparability of research findings seem to be the most serious. Nevertheless, future research should concentrate on mechanisms that make networks productive, while taking into account the difficulties of measuring performance within organizations, such as the performance paradox and the halo-effect.