Anionic water-soluble poly(phenylenevinylene) alternating copolymer: High-efficiency photoluminescence and dual electroluminescence

A facile chemical approach to enhance the photoluminescence of poly (2-methoxy-5-propyloxy-sulfonate- 1,4-phenylenevinylene) (MPS-PPV) by alternately incorporating the rigid p-phenylenevinylene comonomer units into the conjugated backbone is reported. In dilute aqueous solution the resulting anionic conjugated copolymer, poly[(2-methoxy-5-propyloxysulfonate-1,4-phenylenevinylene)-alt-(1,4-phenylenevinylene)] (CO-MPS-PPV), has a fluorescence quantum yield of 51.6%, about an order of magnitude higher than that of the homopolymer. Because of their amphiphilic nature, CO-MPS-PPV chains self-organize into micelle-like aggregates in water. The structure changes of the aggregates can be perceived through monitoring photoluminescence spectra at different solvent compositions and pH values. The fluorescence of the conjugated copolymer Solution is highly sensitive to the cationic surfactant, and emission can be drastically quenched to about 5% of original intensity in the presence of extremely low concentration (26 mu mol/L) of dodecyltrimethylammonium bromide. Such behavior is totally different from its homopolymer counterpart, whose emission is increased by the same surfactant. Water-soluble conjugated polymers with tunable hydrophobic/hydrophilic characteristics afford the diversity of these fluorescence sensory materials. CO-MPS-PPV is also an ideal material for electroluminescence application. The ionic conductivity of CO-MPS-PPV leads to a nearly balanced hole and electron injection from ITO and metal electrodes to the active layer. A light-emitting device fabricated from a composite of CO-MPS-PPV and ionic conducting polyurethane distinguishes from conventional LED by fetching performances like lower turn-on voltage (2 V), light emission under both forward and reverse bias (dual electroluminescence), and fast on/off kinetics (less than 80 ms) under ambient conditions.