Abstract

Fluorenic core oligomers, displaying interesting photoluminescence properties, have been synthesized by an organometallic route. The crystal and molecular structure of a fluorene derivative and three homologous oligomers have been studied. The spiro-derivative of dibromofluorene shows a very strong interaction between the H and Br atoms. The thienyl-terminated oligomer with a spiro-substituent adopts a particular herringbone arrangement with overlap of only the end-thienyl residues, conformationally disordered. The crystal of the all-phenyl derivative consists of the packing of discrete molecules cofacially arranged. The molecule with linear alkyl chains on the 9-position of the fluorene core and thienyl rings as end-groups exhibits polymorphism and its crystal structure, tetragonal, is very peculiar because of the loose 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 photoluminescence 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.