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

The synthesis of a new processable alternating conjugated copolymer consist ing of N-dodecylpyrrole and 2,1,3-benzothiadiazole repeat units (PDPB) is a ccomplished via condensation copolymerization of 2,5-bis(trimethylstannyl)- N-dodecylpyrrole and 4,7-dibromo-2,1,3-benzothiadiazole under the Stille co upling conditions using Pd(PPh3)(2)Cl-2 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 t ransferable monomolecular Langmuir films at the air-water interface. The in teraction between the electron-releasing N-dodecylpyrrole and electron-with drawing 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 photolumi nescence (PL) spectroscopy revealed that in a composite film of PDPB with a methanofullerene (PCBM) as acceptor the fluorescence and the intersystem c rossing 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 char ge carriers.