DYNAMICS OF THE EXCITON BAND AND POLARON DEFECTS OF THE EMERALDINE BASE FORM OF POLYANILINE AS A FILM AND IN SOLUTION
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Date
1992
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Ohio State University
Abstract
Dynamic of the defect states of the emeraldine base form of polyaniline were studied using films and solutions in NMP. Samples were pumped at 2.1 eV and probed at 1.88, 2.0 and 2.9 eV with -5 ps pulses and repetition rates at 500 kHz and 1 MHz. The time-modulation method was incorporated into the study of films to minimize heating effects. We observe transient photoinduced signals on films with a rise time of 8-15 ps, limited by the jitter between pump and probe pulses. More than 50\% of the original photoinduced signals for the thin film samples remain after 5 ns. In contrast to the long time defects of $films^{1}$, decays of the photoinduced signals in fresh solutions contain only fast components ($<$ 50 ps). Solution samples are further oxidized crosslinked slowly under open air, as indicated by blue shifting of the molecular exciton absorption peak. Dynamics of the photoinduced bleaching of the oxidized solution show a slower decay component ($>$5 ns). The influence of electron-torsion angle coupling on electronic properties of polyaniline has been explored $recently.^{2}$. We attribute the differences in decay dynamics of the 2.9 eV polaron band between film and solution to the critical role of free volume to ring rotations and to interchain processes. The fast decay in photoinduced bleaching of the exciton band in solution can be understood by the importance of ring rotation to exciton $stabilization^{3}$. Results of the oxidized solution are compared with results of the dynamics of the pernigraniline base form of polyaniline.
Description
$^{1}$. M. G. Roe, J. M. Ginder, T. L. Gustafson, M. Angelopoulos, A. G. MacDiarmid and A. J. Epstein, Phys. Rev. B {\bf 40} , 4187 (1989). $^{2}$. J. M. Ginder and A. J. Epstein, Phys. Rev. B {\bf 41} , 10674 (1990). $^{3}$. C. B. Duke, E. M. Conwell and A. Paton, Chem. Phys. Lett. {\bf 131} , 82 (1986). $^*$ Work supported in part by DARPA through a grant monitored by USONR and the OSU Center for Materials Reasearch.
Author Institution: Department of Chemistry, The Ohio State University; Department of Chemistry, University of Pennsylvania; Department of Chemistry and Physics, The Ohio State University
Author Institution: Department of Chemistry, The Ohio State University; Department of Chemistry, University of Pennsylvania; Department of Chemistry and Physics, The Ohio State University