Synthesis and Characterization of Luminescent Cyclic Germanium Compounds
The vision in the field of organic electronics is the realization of flexible, easily manufactured, low cost optoelectronics for use in organic light emitting diodes (OLEDs) for large area displays and lighting applications, organic photovoltaic cells, and organic field-effect transistors. The active layers within such devices are composed of semiconducting small molecules or polymers. The rich chemistry of new π-conjugated materials holds the key to continued progress by allowing the material properties of organic semiconductors to be readily tuned towards application specific demands. At the core of this subject matter is how to modify the electronic structures of π-conjugated molecules such that they produce desirable photophysical and optical properties necessary for solid state applications. Significant research has been reported on the syntheses and properties of π-conjugated Group 14 containing molecules over the last two decades for their unique aggregation-induced emission (AIE) whereby a non-emissive chromophore is induced to emit light in condensed phases as well as optoelectronic properties resulting in long wavelength absorption and photoluminescence. The research presented herein focused on the synthetic development and characterization of three classes of germanium-containing semiconductors: germacyclopentadienes, germafluorenes, and a germanium fluorescein analog. Derivatives possessing halogens or alkynyl substituents were synthesized which could be further substituted using conventional halogen-metal exchange or Sonagashira cross-coupling reactions. Based on the current understanding of the AIE photoluminescence processes, structural features prevalent in systems which exhibit this phenomenon were incorporated into the π-conjugated frameworks of several germanium heterocycles in hopes of enhancing their ability to emit with high efficiency in the solid state. Several functionalized heterocycles served as platforms for further investigations of the properties of the electronic structures of these isolated molecules.