Fluorescence dynamics and morphology of electroluminescent polymer in small domains by time-resolved SNOM

The thin film of poly[2-methoxy, 5-(2 ' -ethyl-hexyloxy-p-phenylene vinylene)] (MEH-PPV) was prepared on a glass plate by the spin coating of a chloroform solution. The mesoscopic structures and fluorescence dynamics of the MEH-PPV thin film in small domains were analyzed by AFM and picosecond time-resolved fluorescence SNOM. A wheel structure of MEH-PPV with a sub-mum to a few mum in diameter was found, the size of which was dependent on the position of the film. The formation mechanism of the MEH-PPV wheel and the position dependence of the wheel size were interpreted in terms of the two-dimensional (2D) gas bubble model. A good correlation between the shear-force topography and the fluorescence SNOM image was obtained. The fluorescence decay of the single-chain exciton was found to be much faster in the circumference of the wheel than in the surroundings or the inside of the wheel, which was probably due to the exciton migration among the polymers and trapping by the aggregate of MEH-PPV. (C) 2001 Elsevier Science B.V. All rights reserved.