Polythiophene hybrids of transition-metal bis(salicylidenimine)s: Correlation between structure and electronic properties

The synthesis, electrochemistry, and spectroscopic behavior of tetradentate bis(salicylidenimine) transition metal complexes 5-9 are reported. Appendi ng these complexes with 3,4-ethylenedioxythiophene (EDOT) moieties allows f or electrochemical polymerization at much lower potentials than the parent salen complexes. The resulting polymers display well-defined organic-based electrochemistry at potentials <0.5 V vs Fc/Fc(+). The EDOT-modified N,N'-e thylene bis(salicylidene), N,N'-o-phenylene bis(salicylidene), and N,N'-tra ns-cyclohexylene bis(salicylidene) complexes 5a-b, 6a-b, and 8a-b display c yclic voltammograms with four organic-based redox waves. Increasing the int erchain separation through the use of nonplanar bis(salicylidene) ligands r esults in only two redox waves. The conductivity of the copper-based polyme rs decreases with increasing interchain spacing, with the maximum conductiv ity being 92 S cm(-1) for poly(5a) and 16 S cm(-1) for poly(7a). The nickel complexes were less sensitive to increased interchain separation and showe d conductivities greater than 48 S cm(-1) regardless of the interchain spac ing and near 100 S cm(-1) in the case of poly(6b). In situ spectroelectroch emistry was consistent with the segmented electronic nature of these polyme rs. Cyclic voltammetry of an analogous uranyl complex. 5c, revealed that tw o electrons per repeat unit were removed during oxidation. Consideration of our collective investigations, which also included in situ EPR spectroscop ic studies, led to a postulation that pi-aggregation processes are occurrin g in those polymers which are allowed to have close interchain spacing.