An investigation into the electrical conduction properties of poly(oligo(1-methylpyrrol-2-yl)squaraine)s

The polysquaraines of six oligo(1-methylpyrrole)s have been synthesised and studied for electrical conduction properties. The oligomers used include 1 -methylpyrrole itself, the dimer, the trimer, the tetramer, the hexamer and a mixture of 6-12 1-methylpyrrole units long. The X-ray crystal structures of the trimer and tetramer are reported and provide a valuable insight int o the potential packing of their polysquaraine analogues. Of the series, on ly the tetramer polysquaraine (Sq.Py-4) conducts (2 x 10(-7) S cm(-1)) wher eas the first three members are essentially insulators with dielectric brea kdown values of 1-0.05 MV cm(-1). The X-ray powder diffraction analysis of Sq.Py-4 indicates that this polymer has one-dimensional order with a close interlayer spacing of 3.4 Angstrom, which compares to 3.6-3.8 Angstrom in s everal of the other polymers. This close packing is also evident by the red -purple colouration of Sq.Py-4 while the other polymers are dark blue. The results indicate that a consideration of the solid-state packing of polysqu araines is required before these materials will exhibit some of their predi cted electrical conduction properties. (C) 2001 Elsevier Science B.V. All r ights reserved.