Organic light-emitting vesicles – OLEV

Compartmentalization is a fundamental strategy in building complex hierarchical nano-devices, but understanding communication between distinct molecular architectures will be essential for their operation. Structurally well-defined aggregates, especially artificial vesicles possessing adequate size and stability, may play an important role in future electronic devices, where they can serve to compartmentalize function inside hollow spheres. Thanks to a previous Orchid (PHC 2007 ? 08) project between the two coordinating partners (Bassani, ISM and Wong, NTU), the French and Taiwanese teams established a novel one-step methodology for preparing conjugated ?-structures possessing biuret molecular recognition motifs. In addition to its inherent simplicity and versatility, this methodology does not require the introduction of an inert spacer between the aromatic core and the biuret units. We believe that the absence of a flexible spacer is responsible for the unusual self-assembly properties of these materials: Preliminary investigations showed that these highly luminescent compounds posses the inherent ability to spontaneously self-assemble into vesicles when dissolved in organic solvents. Unlike other examples of vesicle-forming conjugated compounds, the presence of long alkyl substituents or ionic head groups ? both deleterious to charge transport ? is not required. Furthermore, the vesicles are formed spontaneously, without external energy (heating or sonication), or special procedures. During the course of the project, we will pursue methods for controlling the deposition of these light-emitting vesicles on insulating and on conductive surfaces (ITO, metallic surfaces, doped Si). The French partner ISM will investigate information transfer within and in-between immobilized vesicles (exciton migration, charge transport) using state-of-the-art time-resolved confocal fluorescence microscopy. A second French partner, CEA, will study the mechanisms driving vesicle formation in organic media thanks to advanced characterization techniques including X-ray and neutron scattering. Synthesis will be carried out by the Taiwanese partner at NTU, whose previous results showed that it is possible to tailor the electronic energy levels of the vesicles by small modifications of the conjugated core. The resulting compounds will not only cover the entire visible spectrum in terms of fluorescence emission, but will also be suitable to investigate energy transfer processes between individual vesicles. Concomitantly, the electronic properties of the materials will be explored, with special attention to the possibility of employing the vesicles as individual pixels in future OLED displays. The latter would boast unprecedented resolution and would be interesting for miniature displays placed close to the eye, or in embedded systems requiring miniaturization. Two Taiwanese teams, Academia Sinica and Electrical Engineering (NTU), will undertake complete characterization of the electronic properties of material down to the single object level. Together, they possess the know-how and advanced instrumentation (ambient SEM, conducting- and Kelvin force AFM, STM, SNOM) required. We expect these ambitious goals to allow us to significantly and durably advance the field of self-assembled molecular nanotechnology. Thanks to OLEV, we will be able to (i) investigate the electronic properties of vesicles devoid of tunnelling barriers caused by the presence of long alkyl chains; (ii) elucidate the mechanisms of spontaneous self-organization of electroactive moieties into functional assemblies; (iii) investigate electronic communication between nanometric supramolecular assemblies mediated by electron transfer and exciton migration; (iv) Probe the electronic characteristics (conductivity, I/V, electroluminescence, etc.) of individual assemblies. By constructing an ensemble of electro-active compounds designed to self-organize into specific supramolecular aggregates, we will be able to rapidly explore a wide range of combinations in terms of electronic and spectral properties, allowing us to quickly identify and focus on systems displaying interesting properties, such as efficient charge transport or fast exciton migration.