d-xylose-based bolaamphiphiles: Synthesis and influence of the spacer nature on their interfacial and membrane properties

A two-step synthesis, with good yields, of d-xylose-based bolaamphiphiles is described. The monolayer properties, the adsorption behavior and membrane destabilization properties of two bolaamphiphiles differing by their spacers (presence or absence of one double bond) were studied. The presence of one unsaturation has no influence on the interfacial organization at low compression but impairs the stability of the monolayer at high compression. Saturated and unsaturated molecules are suggested to adopt a loop structure at the interface at low compression. The higher degree of freedom of the saturated hydrophobic spacer does not affect the initial diffusion step of the bolaform from the subphase to the interface but greatly slows the arrangement step at the interface. However, once at the interface, their surface-active properties are similar. The higher flexibility of the saturated analogue spacer also greatly increases its lipid vesicle destabilizing property. Its rearrangement within the lipid bilayer is in favour of the formation of inverted phases, facilitating membrane fusion.     

New one- and two-dimensional 4H-pyranylidene NLO-phores

Dipolar, V-shaped compounds derived from 4H-pyranylidene-linked acceptors have been synthesized, and their linear and nonlinear optical properties (displaying μβ values up to 3000 × 10⁻⁴⁸ esu) have been compared to those of analogous one-dimensional derivatives. The pyranylidene ring behaves strictly as a spacer, and not as a donor group.     

Hybrid lamellar silica: combined template extraction and hydrophilic silanation

The surface modification of lamellar silica prepared by liquid crystal templating has been investigated. Two hydrophilic surface modifier agents, 2-glycidoxypropyltrimethoxysilane and 2-[methoxy(polyethyleneoxy)propyl)]trimethoxysilane, have been tested. Characterizations of the modified silica include thermal analysis, (13)C and (29)Si solid state NMR, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The different characterizations confirmed the preservation of the lamellar morphology and the successful surface modification with both silanes along with the template elimination. The results also indicate that the structure and length of the silanes influence the final lamellar organization as well as the grafting yields and mechanisms.     

Synthesis,crystal structure and characterization of 3-thiophene aldehyde thiosemicarbazone and its complexes with cobalt(II), nickel(II) and copper(II)

The reaction of cobalt(II), nickel(II), copper(II) chlorides and bromides with 3-thiophene aldehyde thiosemicarbazone (3TTSCH) leads to the formation of a series of new complexes: [Co(3TTSC)₂], [Ni(3TTSC)₂], [CuCl(3TTSC)]₂, [CuBr(3TTSC)]₂ and [CuBr₂(3TTSCH)]. The crystal structures of the free ligand and of the compound [Ni(3TTSC)₂] have been determined by X-ray diffraction methods. For all these complexes, the central ion is coordinated through the sulfur and the azomethine nitrogen atom of the thiosemicarbazone. [Co(3TTSC)₂], [Ni(3TTSC)₂] and [CuBr₂(3TTSCH)] are mononuclear species, while [CuCl(3TTSC)]₂ and [CuBr(3TTSC)]₂ are binuclear complexes.     

Simple and Versatile Molecular Donors for Organic Photovoltaics Prepared by Metal‐Free Synthesis

Donor–acceptor molecules (D‐π‐A) built by connecting a diphenylhydrazone block to a dicyanovinyl acceptor group via various thiophene‐based π‐conjugating spacers ( 1 – 5 ) were synthesized from mono‐ or dialdehydes by a simple metal‐free procedure. Cyclic voltammetry and UV/Vis absorption spectroscopy show that the extension and/or increase of the donor strength of the spacer produces a decrease of the HOMO and LUMO energy level, a red shift of the absorption spectrum and an increase of the molecular absorption coefficient. Compared to solutions, the optical spectra of spin‐cast thin films of compounds 1–3 show a broadening and red shift of the absorption bands, consistent with the formation of J‐aggregates. In contrast the blue shift observed for the EDOT‐containing compounds 4 and 5 suggests the presence of H‐aggregates. Solution‐cast and vacuum‐deposited films of donors 1–5 were evaluated in solar cells with fullerene C₆₀ as acceptor. A power‐conversion efficiency among the highest reported for bilayer devices of basic configuration was obtained with compound 2 . On the other hand, the results obtained with 4 and 5 suggest that the presence of EDOT in the structure can have deleterious effects on the organization and performances of the donor material.     

Tuning first molecular hyperpolarizabilities through the use of proaromatic spacers

In this paper, we describe the second-order nonlinear optical properties of a series of 1,3-dithiole-based electron donor-acceptor systems incorporating proaromatic donor and spacer groups. Modification of the proaromaticity of the quinoid spacer gives rise to NLO-phores with mubeta values ranging from -2000 x 10(-)(48) esu to +3000 x 10(-)(48) esu. Quite surprisingly, compounds with a p-benzoquinoid spacer and a strong acceptor group show negative mubeta values, usually associated to zwitterionic ground states, and yet they are largely quinoid, as evidenced by crystallographic data and theoretical calculations. Progressive benzoannulation of the spacer and introduction of alkylsulfanyl substituents on the dithiole donor unit result in a shift to more positive mubeta values. DFT and ab initio calculations verify these empirical trends.     

A novel photoreversible photochromic system involving a hydrogen transfer/cyclization sequence

A novel photoreversible photochromic system, 3-(2-benzylbenzoyl)-1,2-R,R(1)-4(1H)-quinolinones/12-hydroxy-5-R-5a-R(1)-6-phenyl-5a,6-dihydrobenzo[b]acridin-11(5H)-ones, is described.