Synthesis and crystal structure and optical properties of fluorenic-core oligomers

Fluorenic core oligomers, displaying interesting PL properties, have been synthesized by organometallic route. The crystal and molecular structure of a fluorene derivative and three omologous oligomers has been studied. Spiro-derivative of fluorene dibromine shows a very strong interaction among H and Br atoms. The thienyl ending oligomer with spiro-substituent adopt a particular herring-bone arrangement with overlap of only end-thienyl residues, conformationally disordered. The crystal of all-phenyl derivative consists of the packing of discrete molecules cofacially arranged. The molecule with linear alkyl chains onto the 9 position of fluorenic core and thienyl ring as end-group exhibits polymorphism and its crystal structure, tetragonal, is very peculiar because of the unclose packing allowing a good separation among adjacent thienyl rings.The absorption and emission properties of this series were investigated and the electroluminescence of single- layer devices was characterized. The PL properties of the molecules are strongly dependent on their structural organization, displaying a red-shift of the emission from the amorphous phase, to the crystalline structure, to the aggregated form. A comparison of the packing of these oligomers and oligothienylenes fully accounts for the optical properties of the reported molecules.