Electronic energy and electron transfer processes in photoexcited donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units.

We investigate the photophysical properties of organic donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units linked by a non-conjugated flexible bridge in solution using complementary optical spectroscopy techniques. When these molecules are diluted in dichloromethane solution, energy transfer from the triphenylene to the perylene diimide excited moieties is evidenced by time-resolved fluorescence measurements resulting in a quenching of the emission from the triphenylene moieties. Simultaneously, another quenching process that affects the emission from both donor and acceptor units is observed. Solution ultrafast transient absorption measurements provide evidence of photo-induced charge transfer from either the donor or the acceptor depending upon the excitation. Overall, the analysis of the detailed time-resolved spectroscopic measurements carried out in the dyad and triad systems as well as in the triphenylene and perylene diimide units alone provides useful information both to better understand the relations between energy and charge transfer processes with molecular structures, and for the design of future functional dyad and triad architectures based on donor and acceptor moieties for organic optoelectronic applications.

Boron difluoride hemicurcuminoid as an efficient far red to near-infrared emitter: toward OLEDs and laser dyes.

A hemicurcuminoid boron difluoride complex is used as an emitter in organic light-emitting diodes, showing far red/near-infrared electroluminescence with an external quantum efficiency as high as 2.1%. This dye blended in CBP thin films shows amplified spontaneous emission with a threshold of 22 µJ cm-2 at 750 nm, making this compound attractive for organic semiconductor lasers operating in the near-infrared region.

[Inlay corneo-conjunctival lamellar graft, preliminary step in surgical treatment of the sequelae of corneal burns]. / Greffe lamellaire cornéo-conjonctivale "inlay", premier temps préparatoire du traitement chirurgical des séquelles de brûlures de cornée.

Surgical rehabilitation of the eye following severe burns is difficult and frequently leads to failure. Penetrating keratoplasty gives functional improvement which is often of short duration because of recurrence of the epithelial defect or because of the gravity of the initial injury. A method which includes a first step before corneal transplantation is described: a lamellar corneo-conjunctival autotransplantation, from the uninjured fellow eye is performed in order to improve the epithelial condition of the injured eye prior to later penetrating keratoplasty. This lamellar graft was performed on 25 patients between 1984 and 1988. Analysis of the results demonstrates the efficacy of the method: no complications were noticed on the grafted or the uninjured eye; visual acuity was improved in 76% of cases; the following penetrating keratoplasty led to a good result (clear graft at one year) in 88% of cases; and in 16% of cases, functional improvement gained with this first surgical step was sufficient to avoid having to carry out the penetrating keratoplasty.

Thixotropic organogels based on a simple N-hydroxyalkyl amide: rheological and aging properties.

The thixotropic properties ofthermoreversible organogels composed ofN-3-hydroxypropyl dodecanamide and various apolar fluids have been investigated by X-ray scattering, light microscopy, and rheo-optics experiments. This revealed that gel formation occurs via a precipitation process. Depending upon the cooling rate, large interconnected aggregates are formed and induce an elastic behavior. When submitted to a shear flow, these aggregates disentangled and became aligned in the direction of the velocity. Nevertheless, shear does not alter the structure of the individual aggregate and connections between the aggregates are quickly rebuilt due to gravity and thermal fluctuations when the applied flow is stopped. The alignment under flow and the reformation of the connections after the cessation of the shear induces the thixotropic behavior.