International audienceSelf-assembled monolayers (SAMs) are rapidly becoming an essential part of organic electronics such as light emitting diodes (LEDs), organic field-effect transistors (OFETs), and complementary circuits, where they are employed to control the morphology and energetics of the interfaces. This review will focus on interface engineering and its influence on such devices. We will describe the growth of SAMs of organic molecules on various surfaces of interest for this purpose (mainly metals and oxides). For the growth of SAMs on metal electrodes, the most common approach makes use of thiols to modify the metal surface, but the preparation of SAMs on dielectrics requires other reactive groups such as carboxylic or phosphonic acids. We review also the control of the interfacial properties by appropriate molecular design of the SAMs and their effect on device performance. SAMs can modify the morphology of the organic semiconductor, the dielectric properties of the insulator, the electronic states at the dielectric interface and the level alignment at the electrode interfaces. All these factors can influence current transport mainly by modifying the charge mobility, the contact resistance and the trap density at the interfaces

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Blue amplified spontaneous emission at room temperature is demonstrated from the exposed face of the strongly emitting organic semiconductor 1,1,4,4-tetraphenyl-1,3-butadiene in single crystal form. The symmetry of the crystal and calculation of lattice sums indicate the J-type organization of the molecular transition moments. The minimum in the lowest exciton dispersion branch, from which emission takes place, is found at the edge of the Brillouin zone leading to a dominant vibronic emission since the zero-phonon line is forbidden. The observed gain narrowed line is attributed to the vibronic replica which becomes amplified with increased pumping. The reported emission is along the normal to the exposed crystal face, important for the development of vertical cavity geometry lasers based on organic single crystals. The threshold excitation fluence of 400 microJ cm(-2) is comparable to other organic crystalline systems, even if the amplification path is much reduced as a consequence of the vertical geometry. Considering these relevant aspects, the optical characterization of this material is provided. The polarized absorption spectra are reported and the properties of the lowest-energy excitonic state investigated. Calculation of the electronic transitions for the isolated molecule, lattice sums for the transition at lowest energy, and the symmetry of the crystal allow attributing the largest face of the samples and the observed optical bands in the spectra. Polarized time-resolved spectra are also reported allowing to identify the intrinsic excitonic emission.

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Stable rubrene derivatives displaying the same crystal packing features as orthorhombic rubrene are synthesized and their solid state properties studied.

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International audienceHerein we describe the synthesis of new substituted tetraaryltetracenes, obtained by the dimerization of triarylchloroallenes, prepared from propargyl alcohols. The propargyl alcohols were prepared by two different synthetic strategies and then the alcohols were treated to obtain the corresponding acenes. In addition to the expected tetracene derivatives, we observed the formation of bis(alkylidene)cyclobutenes. When strong electron-donating substituents were present, the main product was the cyclobutene. We discuss a reaction mechanism that accounts for the formation of the cyclobutenes