Turkish Journal of Physics

Effects of Conformational Disorder on the Conjugation Length and non Linear Optical Properties of Conjugated Polymers




Conjugated polymers are of special interest due to the technological relevance of their nonlinear optical properties for photonic applications. The large non linear responses are in this case associated with the large one dimensional conjugation lengths of the delocalized \pi-electrons. Recent work has concentrated on the nature of conjugation lengths. We study the effect of conformational disorder on the electronic and optical properties of polymers. By taking both steric and conjugation interactions into account, we find that, even if deviations from planar configurations are small, the large angular breaks, although rare are determinative. This leads to a model for the conjugated chain that can be described as relatively long, almost planar segments separated by abrupt breaks in planarity ("flips"). It is the flips that dominate the optical properties. The obtained probability distribution for the segments agrees with results from numerical simulations. We also compare our predictions to recent experiments on long conjugated molecules, and find that our theory provides better agreement over previous models.

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