Synthesis, characterization, and electrooptical properties of a new alternating N-dodecylpyrrole-benzothiadiazole copolymer

The synthesis of a new processable alternating conjugated copolymer consisting of N-dodecylpyrrole and 2,1,3-benzothiadiazole repeat units (PDPB) is accomplished via condensation copolymerization of 2,5-bis(trimethylstannyl)-N-dodecylpyrrole and 4,7-dibromo-2,1,3-benzothiadiazole under the Stille coupling conditions using Pd(PPh3)2Cl2 as a catalyst in dry THF. MALDI-TOF mass spectrometry revealed a perfect alternation of monomer units in PDPB and enabled the identification of hydrogen, bromine, and methyl end groups. As a consequence of its semiamphiphilic nature, PDPB can form stable and transferable monomolecular Langmuir films at the air-water interface. The interaction between the electron-releasing N-dodecylpyrrole and electron-withdrawing 2,1,3-benzothiadiazole units in PDPB results in an optical band gap of 2.03 eV and a red emission. Photoinduced absorption (PIA) and photoluminescence (PL) spectroscopy revealed that in a composite film of PDPB with a methanofullerene (PCBM) as acceptor the fluorescence and the intersystem crossing of the pristine polymer are strongly quenched. Bulk heterojunction photovoltaic cells of PDPB and PCBM (1:3 by weight) have been prepared and demonstrate that in such devices this quenching involves generation of charge carriers.