Novel bifluorene based conjugated systems: synthesis and properties Roberto Grisorio, a Antonio Dell’Aquila, a Giuseppe Romanazzi, b Gian Paolo Suranna, a Piero Mastrorilli, a Pynalisa Cosma, c Domenico Acierno, d Eugenio Amendola, e Giuseppe Ciccarella f and Cosimo Francesco Nobile a, * a Department of Water Engineering and Chemistry (DIAC), Polytechnic of Bari, via Orabona, 4 I-70125 Bari, Italy b Department of Civil and Enviromental Engineering (DICA), Polytechnic of Bari, via Orabona, 4 I-70125 Bari, Italy c Department of Chemistry, University of Bari, via Orabona 4, I-70125 Bari, Italy d Department of Materials and Production Engineering (DIMP), University of Naples Federico II, p.le Tecchio 80, I-80125 Naples, Italy e Institute of Composite and Biomedical Materials (IMCB), Italy’s National Research Council, p.le Tecchio 80, I-80125 Naples, Italy f Dipartimento di Ingegneria dell’Innovazione, University of Lecce, Via Monteroni, I-73100 Lecce, Italy Received 29 July 2005; revised 29 September 2005; accepted 6 October 2005 Available online 2 November 2005 Abstract—A series of novel bifluorene based systems was synthesised by a convergent approach by means of a Suzuki cross-coupling between 7,7 0 -bis-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-9,9,9 0 ,9 0 -tetraoctyl-2,2 0 -bifluorene and suitable aryl-bromides. All the oligomers have been characterized by 1 H, 13 C NMR, FT-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 0 -bis-[5 0 -carbodecaoxy-2,2 0 -bithiophen-5-yl]- 9,9,9 0 ,9 0 -tetraoctyl-2,2 0 -bifluorene (K3.07 eV) is strongly influenced by the presence of the ester functional group. q 2005 Elsevier Ltd. All rights reserved. 1. Introduction During the last two decades, organic semiconducting materials have been the subject of great interest as potentially active layers in opto-electronic devices, in particular in light emitting diodes (LEDs). 1 The easy control of the optical properties and the solubility of the organic materials offers the possibility of lowering the manufactur- ing costs of the devices and improving, in comparison with those based on inorganic substances, some technological aspects. Aiming at a close control both of the physical properties and of the purity of the materials, research efforts have been focused on the synthesis of monodisperse oligomers and well-defined molecules. 2 In particular, oligofluorenes have recently attracted the scientific com- munity, because of their high solubility, good film-forming capability, high luminescence efficiencies 3 and liquid- crystal properties, 4 which make them promising materials for the fabrication of low-cost organic opto-electronic devices. 5 Very recently, circularly polarized light-emission 6 and field effect modulation 7 of oligofluorenes have also been explored. However, the possibility of modulating their features by means of the introduction of specific functional groups has thus far received little attention. In this paper, we propose the synthesis of novel p-conjugated systems based on a bifluorene core substituted in the 7,7 0 positions with different moieties, aiming at investigating how the optical and electrochemical properties are affected by the substituents on the bifluorene core. 2. Results and discussion 2.1. Synthesis and characterization The synthesis of the bis(diphenylamino)-quaterfluorene BF1 is described in Scheme 1. The commercially available 2,7-dibromofluorene (1) was easily converted into the corresponding dioctyl derivative 2, which was used in the synthesis of the boronic ester 3. A Ni(COD) 2 promoted 0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2005.10.010 Tetrahedron 62 (2006) 627–634 Keywords: Functionalised oligofluorenes; Suzuki coupling; Yamamoto coupling; Photoluminescence. * Corresponding author. Tel.: C39 080 5963605; fax: C39 080 5963611; e-mail: nobile@poliba.it