Parallel synthesis of donor-acceptor π-conjugated polymers by post-element transformation of organotitanium polymer

The donor-acceptor type π-conjugated polymers having heterole units were prepared by the reaction of a regioregular organometallic polymer having both reactive titanacyclopentadiene and electron-donor thiophene-2,5-diyl units in the main chain with electrophiles such as diphenyltin dichloride, dichlorophenylphosphine, and diiodophenylarsine. For example, a polymer having electron-accepting phosphole unit was obtained in 54% yield whose number-average molecular weight (M(n)) and molecular weight distribution (M(w)/M(n)) were estimated as 3,000 and 1.9, respectively. The obtained polymer exhibits a high highest occupied molecular orbital (HOMO) and low lowest unoccupied molecular orbital (LUMO) energy levels (−5.13 eV and −3.25 eV, respectively) due to the electron-donating thiophene and electron-accepting phosphole units. Reflecting upon the alternating structure of thiophene and phosphole, the polymer exhibits a band gap energy level (E(g)) of 1.78 eV which is narrower than that of a derivative of poly(thiophene) (E(g) = 2.25 eV).