Main page | Journal list | Log-in

R.F. Bianchi, D.T. Balogh, M. Tinani, R.M. Faria, E.A. Irene

Ellipsometry study of the photo-oxidation of poly[(2-methoxy–5-hexyloxy)-p-phenylenevinylene]

Journal of Polymer Science B 42 (2004) 1033–1041

Poly(p-phenylenevinylene) (PPV) and its derivatives exhibit strong luminescence, being serious candidates to be used as active layers in organic light-emitting diodes. However, the structural degradation caused by photo-oxidation is an obstacle for commercial applications of such materials. Here, we show that spectroscopy ellipsometry is a useful technique to investigate the photo-oxidation of poly [(2-methoxy–5-hexyloxy)-p-phenylenevinylene] (MH-PPV), a PPV derivative, which emits a red color light. Spectroscopy ellipsometry enables determination of the complex dielectric function-ε*(E)-of MH-PPV thin-layer films exposed to air, in the 2.1–4.2 eV energy range, as a function of the light exposure time (te). By using the Lorentz model to fit the experimental ε*(E) curves, it was inferred that the interactions among polymeric chains increase with te. From epsilon*(E), it is also possible to obtain the complex refractive index, N*(E) = n + ik. At higher energies (where k much less than n), n increases from 1.32 to 1.40 with the photo-oxidation progress. The behavior of n was investigated by using the Lorenz–Lorentz equation, taking into account the contribution for it by the chromophores of MH-PPV. The effect of photo-oxidation, mainly due to the replacement of vinyl C=C by the ketone C=O bonds, is confirmed by Fourier transform infrared measurements, an effect that reduces the average effective polymer conjugation length.

Download PDF (163 kB)

Cited Articles

  1. Franta D., Ohlídal I., Munzar D.,
    Parameterisation of the model of dispersion dependences of solid state optical constants,
    Acta Physica Slovaca 48 (1998) 451–458