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The oxidative polymerization of aniline hydrochloride derivatives in water at low temperature is studied without lithium chloride. The resulting polymers have high molecular weight but the conductivity of the acid‐doped films is strongly dependent on the alkyl‐substituted chain at the 2‐positions. The root cause of the alkyl‐substitution effects is thoroughly investigated using density functional theory (DFT) methods (B3LYP using 6–1G(d,p) and 6‐311++G(2d,2p) basis sets). Internal structural changes observed on substitution appear to be more significant than a variety of electronic parameters measured using the natural bond orbital (NBO) method. Interplanar angles steadily increase on substitution, whereas ring orbital properties and the amount of ring delocalization remain fairly constant. An investigation into the extent to which lone pair–σ‐orbital overlap is affected by substitution indicates that increasing the steric bulk of the substituent reduces the ability of the lone pair to delocalize into the ring orbitals. However, the amount of overlap between the two is not adversely affected until the dihedral between them is > 30°, a situation that only occurs in i‐propyl and s‐butyl substitution. This finding is completely reflected in the experimental conductivity measurements.

Publisher's copyright statement:Reprinted with permission from the American Physical Society: Physical Review B 66, 085202 c 2002 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modied, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Temperature-dependent dc conductivity measurements and infrared reflectivity measurements ͑20-9000 cm Ϫ1͒ were performed on a series of polyaniline samples with two different dopant acids at various doping levels. The typical fingerprints of a disordered metal such as a positive temperature coefficient of resistivity at high temperatures, a very high reflectivity in the far infrared, and a plasma resonance have been observed. The results were analyzed in the framework of the Anderson-Mott localization model and considerable consistency between transport studies and optical measurements was obtained. Various parameters enabling a comparative classification of the materials are also reported.

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The device physics of bilayer polymer light emitting diodes containing either poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] or ladder‐type methyl‐poly(p‐phenylene) active layers have been determined. The active layer was consistent in thickness and general preparation whilst hole transporting layers spin cast from emeraldine base polyaniline protonated with camphorsulfonic acid, emeraldine base polyaniline protonated with 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid, and emeraldine base polyaniline protonated with polystyrene sulfonated acid, in various ratios of polyaniline to counter ion, were used in order to determine how various spin‐processible polyaniline layers performed relative to a commercially available polystyrene sulfonated acid doped poly(3,4‐ethylenedioxythiophene layer. For poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] light‐emitting diodes we observe an improvement in performance when using emeraldine base polyaniline protonated with polystyrene sulfonated acid relative to poly(3,4‐ethylenedioxythiophene protonated with polystyrene sulfonated acid, with a maximum device external quantum efficiency of 0.6362 % at a current density of 20.18 mA/cm2.