ALTERNATING, ALL-TRANS POLYENYNES - MODEL COMPOUNDS FOR POLY(DIACETYLENE)S WITH DEFINED CONJUGATION LENGTH

The syntheses of polyenynes as model compounds for poly(diacetylene)s (PDAs) are described. Variation of properties (UV-VIS, Raman, NMR and bond geometries) as a function of the chain length was investigated. After extrapolation to infinite chain length these data were compared to those for PDAs. From UV-VIS spectra a value of lambda = 551 nm (2.25 eV) was calculated corresponding to the electronic transition of a single polyenyne chain. This energy is located at the low energy end of a yellow PDA solution spectrum. From Raman scattering nu((C=C)) = 2108-2128 cm(-1) and nu(C=C)) = 1505-1532 cm(-1) were calculated after extrapolation. Similarly sp-C C-13 NMR data yielded a shift of delta = 100 ppm. These data are almost identical to data known for yellow PDA solutions. Bond geometries are almost identical to those of poly(diacetylene)s and theoretical data.