Synthesis and investigation of cobalt chalcogenide clusters with thienyl phosphine ligands as new acceptor materials for P3HT.

Cobalt selenide clusters with 2-bromo-5-diethylphosphinothiophene (1) and 2-bromo-5-diphenylphosphinothiophene (2) ligands are described. The phosphine ligands are obtained via lithium halogen exchange of 2,5-dibromothiophene followed by addition of chlorodiethylphosphine and chlorodiphenylphosphine, respectively. The prepared phosphine ligands are then sequentially reacted with elemental selenium followed by dicobalt octacarbonyl to yield Co6Se8(P(Et)2(C4H2SBr))6 (3) or Co6Se8(P(Ph)2(C4H2SBr))6 (4), respectively. The two new cobalt selenide clusters were characterized by UV-visible spectroscopy, Fourier-transform infrared spectroscopy, cyclic voltammetry, powder X-ray diffraction, and elemental analysis. Emission spectra were recorded for the addition of, Co6Se8(PEt3)6 (5), 3, and 4 to a 0.004 wt% solution of poly-3-hexyl thiophene (P3HT) in toluene to investigate the charge transport of the system. The quenching of the polymers' emission follows first-order like decay for each cluster. Clusters 3 and 4 are approximately twice as efficient at quenching the emission than cluster 5 with 4 being slightly more efficient than 3. Simple mixtures of 3, 4 or 5 and P3HT were spun cast from toluene into thin films and atomic force microscopy displayed relatively uniform dispersion of 3 and network-like formation of 4 in contrast to the phase separation of 5 in the polymer films.