Palladium-catalyzed polycondensation between 2,5-diiodo-3-hexylthiophene I-Th(Hex)-I with mixtures of p-diethynylbenzene HC=C-Ph-C=CH and alpha,omega-diethynylalkane HC=C(CH2)(1)C=CH (1 = 3 or 8) gives poly(aryleneethynylene) PAE-type copolymers [C = C(CH2)(1)C = C-Th(Hex)](m)[C = C-Ph-C = C-Th(Hex)](n) containing the methylene unit. The copolymers have a molecular weight (M-n) of about 1.2 x 10(4) as determined by GPC (polystyrene standard) and are considered to possess essentially a random sequences in view of the -C = C(CH2)(1)C=C- and -C=C-Ph-C=C-units as judged from their UV-visible spectra. By the incorporation of the (CH2)(1) unit, the lambda(max) position of the corresponding PAE homopolymer [C=C-Ph-C=C-Th(Hex)](n) is shifted to a shorter wavelength. However, the copolymers give rise to a photoluminescence PL peak essentially agreeing with a PL peak of the homopolymer, suggesting occurrence of energy transfer in the copolymer.