Reactive Regioregular Oligothiophenes and Polythiophenes with Zincke Salt Structure: Synthesis, Reactions, and Chemical Properties

Polythiophenes with reactive Zincke salt structure, P4ThPy(+)DNP(Cl-)-a and P5ThPy(+)DNP(Cl-)-a, were synthesized by the oxidation polymerization of oligothiophenes, such as 3'-(4-N-(2,4-dinitrophenyl)pyridinium chloride)-2,2':5',2'';5'',2'''-quarterthiophene (4ThPy(+)DNP(Cl-)) and 4''-(4-N-(2,4-dinitrophenyl)pyridinium chloride)-2,2';5',2'';5'',2''';5''',2''''-quinquethiophene (5ThPy(+)DNP(Cl-)), with iron(III) chloride. The reaction of P5ThPy(+)DNP(Cl-)-a with R-NH2 [R=n-hexyl (Hex) and phenyl (Ph)] substituted the 2,4-dinitrophenyl group into the R group with the elimination of 2,4-dinitroaniline to yield P5ThPy(+)R(Cl-). Similarly, model compounds, 4ThPy(+)R(Cl-) and 5ThPy(+)R(Cl-) (R=Hex and Ph), were also synthesized. In contrast to the photoluminescent 4ThPy and 5ThPy, the compounds P4ThPy(+)DNP(Cl-)-a, P5ThPy(+)DNP(Cl-)-a, and P5ThPy(+)R(Cl-) showed no photoluminescence because their internal pyridinium rings acted as quenchers. Cyclic voltammetry measurements suggested that P4ThPy(+)DNP(Cl-)-a, P5ThPy(+)DNP(Cl-)-a, and P5ThPy(+)R(Cl-) received an electrochemical reduction of the pyridinium and 2,4-dinitrophenyl groups and oxidation of the polymer backbone. P4ThPy(+)DNP(Cl-)-a and P5ThPy(+)DNP(Cl-)-a were electrically conductive (=3.0 x 10(-6) S cm(-1) and 2.1 x 10(-6) S cm(-1), respectively) in the nondoped state. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 481-492