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.