RESUMEN
Sequence-controlled polychalcogenophenes have attracted much interest in terms of synthesis, structure and function in polymer science. For the first time, we developed a new class of alternating block conjugated copolymers denoted as poly(alt-AB)x-b-(alt-AC)y where both blocks are constituted by an alternating copolymer. 3-Hexylthiophene (S), 3-hexylselenophene (Se) and 3-hexyltellurophene (Te) are used as A, B and C units to assemble three sequence-controlled polychalcogenophenes P(SSe)b(STe), P(SSe)b(SeTe) and P(STe)b(SeTe) which are prepared by adding two different Grignard monomers in sequence to carry out Ni(dppp)Cl2-catalyzed Kumada polymerization. The molecular weight, dispersity, and length of each block (x = y) and main-chain sequence can be synthetically controlled via the catalyst transfer polycondensation mechanism. The polymer structures, i.e. alternating block main chain with high side-chain regioregularity, are unambiguously confirmed by 1H-NMR and 13C-NMR. The optical and electrochemical properties of the polymers can be systematically fine-tuned by the composition and ratio of the chalcogenophenes. From GIWAXS measurements, all the polymers exhibited predominantly edge-on orientations, indicating that the packing behaviors of the alternating block polychalcogenophenes with high regioregularity are inherited from the highly crystalline P3HT. P(SSe)b(STe) exhibited a hole OFET mobility of 1.4 × 10-2 cm2 V-1 s-1, which represents one of the highest values among the tellurophene-containing polychalcogenophenes. The tellurophene units in the polymers can undergo Br2 addition to form the oxidized TeBr2 species which results in dramatically red-shifted absorption due to the alternating arrangement to induce strong charge transfer character. The OFET devices using the tellurophene-containing polychalcogenophenes can be applied for Br2 detection, showing high sensitivity, selectivity and reversibility.
RESUMEN
Three unsymmetrical diiodobichalcogenophenes SSeI2, STeI2, and SeTeI2 and a diiodoterchalcogenophene SSeTeI2 were prepared. Grignard metathesis of SSeI2, STeI2, SeTeI2, and SSeTeI2 occurred regioselectively at the lighter chalcogenophene site because of its relatively lower electron density and less steric bulk. Nickel-catalyzed Kumada catalyst-transfer polycondensation of these Mg species provided a new class of side-chain regioregular and main-chain AB-type alternating poly(bichalcogenophene)s-PSSe, PSTe, and PSeTe-through a chain-growth mechanism. The ring-walking of the Ni catalyst from the lighter to the heavier chalcogenophene facilitated subsequent oxidative addition, thereby suppressing the possibility of chain-transfer or chain-termination. More significantly, the Ni catalyst could walk over the distance of three rings (ca. 1 nm)-from a thiophene unit via a selenophene unit to a tellurophene unit-to form PSSeTe, the first ABC-type regioregular and periodic poly(terchalcogenophene) comprising three different types of 3-hexylchalcogenophenes.