Photomechanical actuation and manipulation of the electronic properties of linear pi-conjugated systems

A photodynamic molecular architecture has been synthesized by covalent fixation of a photoisomerizable azobenzene group at two fixed points of a conformationally flexible pi-conjugated quaterthiophene chain. The crystallographic structure shows that the two systems lie in parallel planes with a short interplane distance. Theoretical modelization and experimental analysis by 1H NMR and cyclic voltammetry unequivocally show that trans to cis photoisomerization of the azobenzene group induces dimensional and conformational changes in the underlying pi-conjugated system. These geometrical changes produce, in turn, an increase of the HOMO level and a narrowing of the HOMO-LUMO gap, thus providing a first example of photomechanical control of the electronic properties of the pi-conjugated system.     

Rheology of nanosized hairy grain suspensions

Suspensions of nanosized hairy grains have been prepared by grafting long polydimethylsiloxane chains (molecular weight ) onto silica particles (radius ), dispersed into a good solvent of PDMS. Depending on the particle volume fraction, different rheological behaviors are observed. In the very dilute regime, the suspensions are perfectly stable and the particles behave almost as hard spheres: flow penetration inside the corona is then very weak. When the particle volume fraction goes to the close packing volume fraction, the suspension viscosity does not diverge as for hard spheres due to the increase of flow penetration inside the corona and to corona entanglements. The particles have then the same behavior as polymer stars having an intermediate number of arms (). Finally, in the concentrated regime (), the suspensions form irreversible gels. We shown that this unexpected gelation phenomenon is related to the presence of the silica cores: grafted PDMS chains can adsorb onto different particles and form irreversible bonds between the cores. The viscosity and elastic modulus evolutions during gelation are well described by the scalar percolation model of sol-gel transition. Received 23 March 1998     

Desymmetrization of Perylenediimide Bay Regions Using Selective Suzuki–Miyaura Reactions from Dinitro Substituted Derivatives

Bay decoration of perylenediimide (PDI) is an attractive approach for tuning the optoelectronic properties of the dye as well as breaking backbone planarity, which provides the possibility of preventing the undesired formation of aggregates. This is usually performed through successive bis-bromination of PDI and pallado-catalyzed cross-coupling, which leads to symmetric triads. We now describe an efficient synthetic strategy for desymmetrization of the accepting PDI core by starting from its bis-nitration. To this end, Suzuki–Miyaura Couplings (SMC) were carried out on a mixture of 1,6- and 1,7-dinitroPDI regioisomers to add triphenylamine donating moieties and obtain donor–acceptor–donor triads. Investigation of the reactivity of dinitro PDI derivatives toward SMC has allowed us to access unprecedented asymmetric π-conjugated PDI-centered triads. These 1,6- and 1,7-PDI based triads, prepared as regioisomeric mixtures, were successfully separated and their spectroscopic, crystallographic and optoelectronic differences are reported.     

Determination of suspected allergens in non-volatile matrices using PTV injection with automated liner exchange and GC-MS

A method is described for the analysis of suspected volatile allergens in products containing high molecular weight or non-volatile compounds such as plant extracts, solid and liquid detergents, shampoos, etc. The method is based on dissolution/extraction of the sample followed by direct injection in a programmed temperature vaporizing inlet, the liner of which contains PDMS foam to retain the high molecular weight non-volatile material. The liner is automatically replaced after each injection, by an automated liner exchange device. Analysis is done by GC-MS operated in the retention-time locked mode. The figures of merit are illustrated with the analysis of some real samples.     

Benzyl Derivatives of 3-Phenoxytoluene

3-phenoxybenzyl derivatives are of great interest in the chemistry of the pyrethroid insecticids since its chrysanthemate and isovalerate esters are the most active compounds against insects and the less toxic towards mammals.¹ However classical benzylic catalytic methods give poor yields in the case of the 3-phenoxytoluene, because of the deactivating effect of the 3-phenoxy substituent upon the benzylic hydrogen^2,3.     

Extraction, thermal cleanup, and GC/MS quantification with disposable solid extractants: application to hydrophobic analytes in aqueous surfactant solutions

Fragranced consumer products are generally formulated together with surfactants. In application, these products are often highly diluted with water. Analyzing trace amounts of fragrance ingredients in such mixtures is challenging and usually requires either time‐consuming sample cleanup or extensive cleaning of the trapping device to avoid memory effect and cross‐contamination between samples. To overcome these limitations, a new disposable extraction device has been developed to be used in combination with a thermodesorption–GC–MS unit. Made of PDMS foam cylinders, it efficiently extracts trace amounts of hydrophobic compounds from complex aqueous solutions and provides an online sample cleanup, thanks to the controlled desorption temperature, which allows retaining the low volatile constituents of the matrix within the absorptive foam. Combined with a stable isotope dilution assay, accurate quantifications of Cetalox^®, Muscenone?, Helvetolide^®, Polysantol^®, Dartanol, and Myrrhone^® from aqueous solution containing surfactant and from water from the aeration tank of a sewage plant were successfully conducted. LOQ varied between 1 and 25 ppb (20% confidence interval, α=0.1).     

Interactions between cisplatin derivatives and mobile phase during chromatographic separation

Summary Althoughcis-dichlorodiammineplatinum(II) (cisplatin or CDDP) is widely used for the treatment of several kinds of tumour, its stability and metabolism in biological fluids have not been completely elucidated. Conditions in which mobile phases of formic or phosphoric acids interact with platinum derivatives during chromatographic separation performed by high performance liquid chromatography on-line with inductively coupled plasma-mass spectrometry (ICPMS) are investigated. During chromatographic separation of CDDP the formic acid mobile phase does not interact with CDDP itself nor with its hydrolysis products. In contrast, the phosphoric acid mobile phase interacts, not with the CDDP itself, but with its hydrolysis products which are present only in an aged aqueous solution, to generate two platinum phosphato-derivatives. This study suggests that the phosphoric acid has greater affinity for the CDDP hydrated complexes than formic acid and the latter is more appropriate for the study of cisplatin behavior in aqueous and biological media.     

Mechanical Modulation of the Solid-State Luminescence of Tricarbonyl Rhenium(I) Complexes through the Interplay between Two Triplet Excited States

Mechanoresponsive luminescence (MRL) materials promise smart devices for sensing, optoelectronics and security. We present here the first report on the MRL activity of two Re^I complexes, opening up new opportunities for applications in these fields. Both complexes exhibit marked solid-state luminescence enhancement (SLE). Furthermore, the pristine microcrystalline powders emit in the yellow-green region, and grinding led to an amorphous phase with concomitant emission redshift and shrinking of the photoluminescence (PL) quantum yields and lifetimes. Quantum chemical calculations revealed the existence of two low-lying triplet excited states with very similar energy levels, that is, ³IL and ³MLCT, having, respectively, almost pure intraligand (IL) and metal-to-ligand charge-transfer (MLCT) character. Transition between these states could be promoted by rotation around the pyridyltriazole−phenylbenzoxazole bond. In the microcrystals, in which rotations are hindered, the ³IL state induces the prominent PL emission at short wavelengths. Upon grinding, rotation is facilitated and the transition to the ³MLCT state results in a larger proportion of long-wavelength PL. FTIR and variable-temperature PL spectroscopy showed that the opening of the vibrational modes favours non-radiative deactivation of the triplet states in the amorphous phase. In solution, PL only arises from the ³MLCT state. The same mechanism accounts for the spectroscopic differences observed when passing from crystals to amorphous powders, and then to solutions, thereby clarifying the link between SLE and MRL for these complexes.