Luminescence properties of poly[1,4-phenylenevinylene-co-(2,3,5,6-tetramethyl-1,4-phenylenevinylene)] – Improved EL efficiency through partial disruption of main chain π-conjugation by substituents

Two copolymers of poly(p-phenylenevinylene) (PPV) containing low levels (0.8 and 3.6 mole %) of the 2,3,5,6-tetramethyl-1,4-phenylenevinylene (TMPV) units were prepared via the sulfonium salt precursor route. The luminescence properties of the two copolymers were studied in detail mainly for photoluminescence (PL) and electroluminescence (EL) characteristics in comparison with those of PPV itself. Inclusion of low levels of TMPV units improves EL efficiency by more than 10 times when a single layer device was constructed using ITO coated glass anode and aluminum metal cathode. This was explained by the possible partial disruption of main chain π-conjugation by the TMPV units which force its phenylene or vinylene structure to twist out of the coplanar structure in order to avoid of the steric repulsion between the methyl and vinyl protons in the TMPV units. The UV-vis, PL and EL spectra of the copolymers support this supposition.