The Ni=Si=N link as electron accepting moiety for stable, solution-processable conjugated oligomers

New conjugated oligomers, oligo(9,9-didodecylfluorene-bis-sulphurdiimide), consisting of 9,9-didodecylfluorene separated by -Ni=Si=N- moieties, are reported. These oligomers are stable purple solids under ambient conditions with absorption covering a broad spectral window in the UV-vis range and a main broad peak centered at 555 nm with onset extending to 700 nm. These oligomers show an obviously longer conjugation length than its dimeric analogue, bis-9,9-didodecyl-fluorene-2-sulfurdiimide that shows a band-edge absorption centered at 484 nm with onset at 590 nm. The dimer and oligomers are soluble in a variety of organic solvents. Moreover, we found that the oligomer with an average repeating-unit number of six could significantly quench the photoluminescence (PL) of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4- phenylene vinylene] (MEH-PPV) or poly(3-hexylthiophene) (P3HT) in the solid state. More importantly, the composites of this oligomer with P3HT showed a nearly 10-fold enhancement of the photocurrent, compared with that of P3HT itself. In addition, the PL of this oligomer could be quenched by the presence of phenyl-C₆₁-butyric acid methyl ester (PCBM) in toluene. These results suggest the presence of photoinduced charge transfer in composites of these oligomers blended with an electronic partner that either donates or accepts electrons.