Star-like Aromatic Conjugated Polymers and Dendrimers for OLEDs
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D10.6.1
Star-like Aromatic Conjugated Polymers and Dendrimers for OLEDs Irina A. Khotina1, Diana Yu. Baranova1, Natalia S. Burenkova1, Anastasia A. Gurskaja1, Peter M. Valetsky1, Lyudmila M. Bronstein2 1
A.N.Nesmeyanov Institute of Organoelement Compounds Russian Academy of Sciences, Vavilova str. 28, 117813, Moscow, Russia 2 Department of Chemistry, Indiana University, Bloomington, IN 47405, U.S.A. ABSTRACT Highly branched photoluminescent polyphenylenes (PP) containing 1,3,5triphenylbenzene (TPB) fragments were prepared via combination of cyclocondensation of acetylaromatic compounds and Ni0-catalyzed dehalogenation. Defect free PP with star-like fragments were synthesized using Ni0-catalyzed polymerization of aromatic bromides obtained by modification of 1,3,5-tri(p-bromophenyl)benzene. The molecular weights of the polymers were 6700, 8600, and 15300 Da. The maximum photoluminescence in solution (quantum yield of 96%) was obtained for the highly branched polymer with star-like TPB fragments, bearing no Br or acetyl groups. The PP of this kind show also very bright fluorescence in a solid state under UV irradiation at 360 nm so they can be considered as promising materials for OLED applications. INTRODUCTION The discovery of electroluminescence in a polymer semiconductor has led to intensive research in the field of organic light emitting diodes (OLEDs). Polyphenylenes (PP) are π–conjugated polymers drawing a considerable interest from the mid sixties as thermally stable materials [1]. Nowadays polyphenylenes are again in the focus of attention because of their luminescence [2], and therefore the possibility of using in OLEDs [3]. Wide bandgaps allowing emission of blue light (400-450 nm) are typical for polyphenylenes. The development of effective long-lived blue emitters remains a significant challenge in the field of OLEDs [4]. PP can be synthesized using different avenues [5 - 8]. The majority of recent works were focused on linear PP [4, 8]. One of the successful methods to synthesize linear PP is Ni0-catalized homopolymerization of aromatic dibromides or dichlorides [7 - 11]. This method leads to defect-free structures and seems to be promising for synthesis of polyphenylenes designed for optoelectronic devices. Normally linear poly-p-phenylenes (PPP) are insoluble in organic solvents that strongly limits their potential application for OLED. A reasonable way to increase solubility is to insert side groups in linear macromolecules and also to synthesize very branched polymers containing no other substituents in main chain than benzene rings. Preparation of branched polyphenylenes containing 1,3,5-triphenylsubstituted benzene rings was described in early 90-s [12, 13]. The synthesis was based on a AB2-type monomer which, in turn, was synthesized from 1,3,5-tribromobenzene by substitution of one bromine group with MgX group by Grignard reaction [13] or with B(OH)2 group by Suzuki reaction [12, 13]. The polymers prepared by these methods had low molecular weight and majority of them were soluble in common sol
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