Molecular assembling of pi-conjugated poly(pyrimido[5,4-d]pyrimidine-2,6-diyl)s prepared by organometallic polycondensation

pi-conjugated poly(pyrimido[5,4-d]pyrimidine-2,6-diyl)s prepared by an orga nometallic polycondensation and having long side chains are considered to t ake an end-to-end type packing in the solid as judged from their X-ray diff raction patterns. Their W-visible spectra show a main absorption peak at ab out 450 nm, supporting the presence of an expanded pi-conjugation system.