4-Vinylpyridine (4VP) and N,N-dimethylacrylamide (DMAA) were polymerized in a controlled manner using a β-phosphonylated nitroxide (N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide, commonly designated as DEPN) as a control agent. Compared to the results that had previously been reported for the nitroxide-mediated radical polymerization (NMRP) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), the polymerization of 4VP was much faster and very well controlled up to higher monomer conversions. Unlike 4VP, the controlled radical polymerization of DMAA using different types of nitroxides had so far remained limited to a very low conversion range (typically inferior to 10%). The use of DEPN gave rise to a very significant improvement of the NMRP of DMAA by providing a good reaction control up to high conversion (approximately 60%). For the first time, the ability of DEPN to control the homopolymerization of DMAA even at high conversion allowed the synthesis of poly(DMAA-b-4VP) block copolymers with a hydrophilic poly(DMAA) block which was longer than the poly(4VP) block. This particular feature should fairly improve the hydrosolubility of the derived amphiphilic cationic polymers, which can be obtained by simple quaternization of the former block copolymers, and extend the scope of their applications.

The free radical polymerization of 4-vinylpyridine (4VP), using 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) radical as a capping agent, proved to proceed in a pseudo-living manner, providing low polydispersity P4VP whose chain growth could be controlled. The original nitroxide concentration was revealed to have no obvious influence on the rate of polymerization, whereas it could be directly related to the molecular weight of the polymer. The polydispersity was shown to increase within the range 1.02−1.50. The influence of temperature on the kinetics of the reaction was demonstrated, but no significant effect could be found on the molecular weights and polydispersities of the macromolecules.

: Non-doped white organic light-emitting diodes using an ultrathin yellow-emitting layer of rubrene (5,6,11,12-tetraphenylnaphtacene) inserted on either side of the interface of a holetransporting α-NPB (4,4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl) layer and a blue-emitting DPVBi (4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl) layer are described. Both the thickness and the position of the rubrene layer allow fine chromaticity tuning from deep blue to pure yellow via a bright white (WOLED) with CIE coordinates (x= 0.33, y= 0.32), a η ext of 1.9%, and a color rendering index (CRI) of 70. Such a structure also provides an accurate sensing tool to measure the exciton diffusion length in both DPVBi and NPB (8.7 and 4.9 nm respectively). Organic light emitting devices (OLEDs) are a promising technology for fabrication of full-color flatpanel displays. The development of OLEDs relies on the capability to obtain emission spanning the full visible spectrum. In particular, White OLEDs (WOLEDs) are of foremost interest for lighting and display applications 1 . To achieve white emission, various methods have been used, such as e.g. excimer/exciplex emission 2 , mixing of three (red, blue, green) or two (complimentary) colors in a single host matrix  or in physically separate layers 3 . Among these various devices, numerous doped-type WOLEDs using two mixed complimentary colors to produce white have been fabricated 4,5 . Although the co-evaporation process allows to a certain extent a control of the emitted radiation color via the different evaporation rates, it remains technologically difficult to accurately control the concentration. Hence, fine tuning of the color and achievement of bright white emission remain problematic. We report in this letter on a way to finely tune the color, including balanced white emission, in a multilayer non-doped OLED 6,7 based on blue matrices, in which an ultrathin yellow emitting layer was inserted. We show that by adjusting both the thickness and position of this layer, a very accurate control of the emitted color can be obtained, from deep blue with CIE coordinates (0.17, 0.15) to pure yellow (0.51, 0.48), via a bright white (0.32, 0.31) close to the equi-energy white point (0.33, 0.33), and a quite good Color Rendering Index (CRI) of 70. The external quantum efficiencies, the chromaticity coordinates and the luminance values are investigated for various thicknesses and positions of the yellow-emitting layer. Finally, the device structure, sometimes referred as "delta doping" 8 , allows a better understanding of the emission process through an experimental determination of the exciton lengths.The 0.3 cm 2 -active-surface OLED-structure consists of the different layers described in fig. 1. The Indium Tin-Oxide (ITO)-covered glass substrate was cleaned by sonication in a detergent solution, then in deionized water and prepared by a UV-ozone treatment. Organic compounds were deposited onto the ITO anode by sublimation under high vacuum (10 -7 Torr) at a rate of 0.1 -0.2 nm/s. An ...