Synthesis and Characterization of Photoluminescent 3,4-Ethylenedioxythiophene Derivatives

We report the synthesis of novel 3,4-ethylenedioxythiophene (EDOT) derivatives and the investigation of their photoluminescent properties. Lithiation of EDOT followed by the conversion to the 2-substituted zinc chloride or Grignard derivatives (useful for subsequent coupling reactions using organopalladium and organonickel chemistry) led to the formation of 2,5-bis[(3,4-ethylenedioxy)thien-2-yl]-thiazole ( 1), 2,5-bis[(3,4-ethylenedioxy)thien-2-yl]-3-alkylthiophene ( 2, 3 ), and 2,5-bis[(3,4-ethylenedioxy)thien-2-yl]-toluene ( 4) . The lithiated EDOT provided a route for the formylated species followed by a Knoevenagel condensation which led to the cyanovinylene derivatives 1,4-bis[1-cyano-2-{(3,4-(ethylenedioxy)thien-2-yl}vinyl]benzene ( 5), 1,4-bis[1-cyano-2-{(3,4-(ethylenedioxy)thien-2-yl}vinyl]-2,5-dimethoxybenzene ( 6 ). The lithated EDOT also provided a convenient method for preparation of 2,5-bis[(3,4-ethylenedioxy)thien-2-yl]-1,3,4-oxadiazole ( 12 ) by the hydrazide method. These materials exhibit blue to red emission characteristics with quantum yields ranging from 3.2 to 9.0%. Cyclic voltammetry shows oxidation potentials ranging from 422 to 617 mV. The prepared monomers may be used as optical building blocks in other unique polymer systems.