Synthesis of phenylbutadiynylpyridinium derivatives for nonlinear optics

1- Methyl- 4-{[ 4-( dimethylamino) phenyl] butadiynyl} pyridinium ( PBP) derivatives with iodide or benzenesulfonate anion were synthesized as potential compounds for both second- and third- order NLO applications. PBP shows peculiar absorption spectrum in methanol, in which molar extinction coefficient at absorption maximum ( lambda(max)) decrease irrespective of bathochromic shift of lambda(max) compared with the corresponding compound with one triple bond between two aromatic rings. From semiempirical MO calculations, it was explained by aromatic- ring rotation of PBP in methanol. Activity on second- harmonic generation ( SHG) was found in four out of thirteen compounds synthesized. Although most of PBP derivatives were found to show exothermic reaction before melting, pure solid- state polymerization was not confirmed in these compounds.