New polydiacetylenes (PDAs) have been prepared in which a ligating 2,2'- bipyridyl substituent is incorporated in the side-chain, 3a-d. The formation of complexes of these polymers, and of a related (diethylamino)alkyl substituted PDA 4, with transition metals has been studied. Coordination polymers containing nickel(II) 5a,b, copper(II) 5c,d, ruthenium(II) 6 and molybdenum(o) 7a-c have been formed and characterised spectroscopically by comparison with appropriate model coordination compounds, including species derived from corresponding monomeric 1,3-diynes 1. The nonlinear optical properties of PDA 4 and the coordination polymers 5-7 in solution have been investigated by the z-scan procedure. Values for the nonlinear absorption coefficient, a2, and the nonlinear refractive index, n2, have been derived and these are discussed in relation to the structures of the PDAs.