Several alternating and semi-alternating copolymers were analysed by quaternary C-13 n.m.r. spectroscopy. The aromatic 'next to polymer chain' carbon (C7) of donor monomer (1) units is sensitive to the unit 1-centred triad sequence distribution. The acceptor monomer is referred to as 0. The chemical shifts of the non-alternating (111), semi-alternating (011 + 110) and alternating (010) triad sub-peaks were assigned in ppm in Table 1.