New Poly(p-phenylene vinylene) Derivatives with Two Oxadiazole Rings per Repeat Unit: Synthesis, Photophysical Properties, Electroluminescence, and Metal Ion Recognition JOHN A. MIKROYANNIDIS, 1 IOAKIM K. SPILIOPOULOS, 1 THEODOROS S. KASIMIS, 1 ABHISHEK P. KULKARNI, 2 SAMSON A. JENEKHE 2 1 Chemical Technology Laboratory, Department of Chemistry, University of Patras, GR-26500 Patras, Greece 2 Department of Chemical Engineering and Department of Chemistry, University of Washington, Seattle, Washington 98195 Received 13 November 2003; accepted 7 January 2004 ABSTRACT: Two new poly(p-phenylene vinylene) derivatives OX1-PPV and OX2-PPV bearing two 1,3,4-oxadiazole rings per repeat unit and a fully conjugated backbone with solubilizing dodecyloxy side groups were synthesized and investigated. The amorphous conjugated polymers had glass-transition temperature values of 60 –75 °C and emitted intense blue or greenish-blue light in solution with photoluminescence (PL) emission maxima at 379 – 492 nm and PL quantum yields of 0.41– 0.52. In the solid state they emitted yellowish-green light with PL emission maxima at 533–555 nm. Cyclic volta- mmetry showed that both conjugated polymers had reversible reduction and irrevers- ible oxidation, making them n-type materials. The electron affinity of OX2-PPV was estimated as 2.85 eV whereas that of OX1-PPV was 2.75 eV. Yellow electrolumines- cence (EL) was achieved from single-layer light-emitting diodes of OX2-PPV with an EL emission maximum at 555 nm and a brightness of 70 cd/m 2 . Polymer OX2-PPV, which was functionalized with 2,6-bis(1,3,4-oxadiazole-2-yl)pyridine, demonstrated sensitiv- ity to various metal ions as a fluorescence-mode chemosensor. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2112–2123, 2004 Keywords: poly(p-phenylene vinylene); oxadiazole; photoluminescence; electrolumi- nescence; light-emitting polymers; light-emitting diodes (LED); fluorescence; photo- physics; synthesis INTRODUCTION Organic light-emitting diodes (OLEDs) based on poly(p-phenylenevinylene) (PPV) and other conju- gated polymers have attracted a great deal of interest in the past decade for potential applica- tions in a new generation of flat-panel displays. 1–7 Many important and fundamental challenges still remain, including maximization of the external quantum efficiency, synthesis of new stable ma- terials for pure saturated colors, and modes of addressing pixels for a full-color red-green-blue display with high resolution. Electrolumines- cence (EL) in OLEDs arises from the recombina- tion of electrons and holes in the emissive poly- mer layer that are injected from the two opposite electrodes to form excitons, which decay radia- tively to give light. To achieve high EL efficiency, it is necessary to balance the rates of injection and transport of electrons and holes in the EL device. Most conjugated polymers, such as PPVs, Correspondence to: J. A. Mikroyannidis (E-mail: mikroyan@chemistry.upatras.gr) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 42, 2112–2123 (2004) © 2004 Wiley Periodicals, Inc. 2112