Novel bifluorene based conjugated systems: synthesis and properties

A series of novel bifluorene based systems was synthesised by a convergent approach by means of a Suzu'ki cross-coupling between 7,7'-bis-(4,4,5,5-tetramethyl-[1,3,2]dioxaboi-olan-2-yl)-9,9,9,9'-tetraoctyl-2,2'-bifluorene and suitable aryl-bromides. All the oligomers have been characterized by H-1, C-13 NMR, Fr-IR, UV-vis, PL spectroscopy and mass analyses. In particular, it has been demonstrated that the presence of strong electron donor (amines) or withdrawing (carboxylic esters) groups causes a bathochromic shift of the optical properties with respect to those of unsubstituted molecules. The effects of these functional groups on the HOMO-LUMO energy levels were investigated by cyclic voltammetry. Remarkably, the LUMO energy level of 7,7'-bis-[5-carbodecaoxy-2,2'-bithiophen-5-yl]-9,9,9',9'-tetraoctyl-2,2'-bifluorene (-3.07 eV) is strongly influenced by the presence of the ester functional group. (c) 2005 Elsevier Ltd. All rights reserved.