The compound 4,4-difluoro-4-borata-3a-azonia-4a-aza-sindacene, more commonly known as BODIPY, has enjoyed a high and rapidly escalating level of interest over the past decade.1 This dye-type material, which can be likened to a porphyrin subunit, has been studied mainly in applications related to its strong absorption and fluorescence properties. 2,3 Recent examples of the applications of BODIPY include biological tags with visible/near IR emission, 4,5 mechanical rotors, 6 lasing, 7-9 dye sensitized solar cells, 10 electroluminescence (EL), 11 and electrogenerated chemiluminescence (ECL).
12The incorporation of the BODIPY unit into conjugated polymers (CPs) is a fascinating prospect. In particular, the strong absorption/emission and tunable color characteristics 13 of BODIPY derivatives mark them as ideal components in copolymers for electrochromic, optoelectronic, and organic solar cell devices. To the best of our knowledge, BODIPY has not been studied as a main chain component in conjugated macromolecular structures, although an organoboronpolymer 14 andaBODIPY-quaterthiophene-BODIPY triad have been reported 15 and a series of BODIPY dyes have been used in blends with CPs for organic solar cell devices.
16In addition to their electronic properties, BODIPY derivatives also exhibit variable redox chemistry, and they have been used as electron donors 17 and acceptors. 18 In the latter case, BODIPY comonomers have the potential of lowering the band gap of CPs (and stabilizing their reduced states), since donor and acceptor units within conjugated structures are able to bring the HOMO/LUMO energy levels closer together. For organic solar cell applications low band gap CPs are highly desirable, but the stability of doped states is often poor in such materials. A recent and appropriate example is given by poly(acenaphtho [1,2-b]19 which has a remarkably low band gap of approximately 0.5 eV but demonstrates very poor reversibility upon p-doping.In this work, we report the synthesis of a conjugated polymer containing the BODIPY structure as a main chain component. The material has a low band gap of approximately 0.8 eV, and the reversibility of both n-and p-doping processes in this polymer is outstanding. The synthesis of the monomer unit (3) is summarized in Scheme 1. Functionalization of the BODIPY unit with 3,4-ethylenedioxythiophene (EDOT) was chosen because of the wellknown facile electropolymerizability of the EDOT unit and its derivatives.20 A mixture of 3,5-dichloro-8-(4-nitrophenyl)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene 1, 21 2-(trimethyltin)-3,4-ethylenedioxythiophene 2, 22 and tetrakis(triphenylphosphine)palladium(0) was reacted in anhydrous DMF over 2 h at 160°C via microwave assisted heating. The product was purified by column chromatography and recrys-