BAND-GAP ENGINEERING OF DONOR-ACCEPTOR-SUBSTITUTED PI-CONJUGATED POLYMERS

Three series of alternating donor-acceptor-substituted co-oligomers (w ith different chain lengths) have been prepared by application of the Pd-catalyzed Stille coupling methodology. They contain pyrrole or thio phene as the electron-rich unit and quinoxaline or 2,1,3-benzothiadiaz ole as the electron-deficient unit. The trimethylstannyl group is alwa ys located on the electron-rich unit, whereas the bromo substituent is always located on the electron-deficient one. The tBoc-protecting gro up is used in the synthesis of the pyrrole-containing oligomers. The i ncremental bathochromic shift of lambda(max) upon chain elongation of the three series of oligomers is less than that of the homooligomers o f thiophene and pyrrole; this decrease is caused by a diminished dispe rsion of the LUMO level upon chain elongation. This conclusion was dra wn after comparing the oxidation and reduction behavior of the thiophe ne/benzothiadiazole co-oligomers with that of thiophene oligomers. The incremental bathochromic shift is similar for all three series of oli gomers and is used as a tool in the band-gap engineering of donor- acc eptor-substituted pi-conjugated polymers.