We have synthesized coloured monomer structures characterized by the simultaneous existence of a polarizable double bond and an extended chromophore. The polymerization and copolymerization of these monomers have been tested with styrene and methyl methacrylate. The third-order nonlinear optical (NLO) properties of different samples have been studied from their solutions using chloroform as solvent. The third-order hyperpolarizability gamma(xxxx) of the better materials can reach 10(-29) esu at 532 nm and their response time is faster than 35 ps. The corresponding third-order NLO susceptibility X-xxxx((3)) is estimated to be 6 x 10(-11) esu and the figure of merit X-(3)/alpha = 7.510(-2) esu cm is larger than that of most currently known nonlinear optical polymers. (C) 2000 Elsevier Science Ltd. All rights reserved.