Decreasing the aggregation and ligand redox potential of metallophthalocyanines through branched ether functionalization

Abstract

The addition of ether functional groups to a metallophthalocyanine ring is known to significantly decrease the oxidation potentials of the ring. In this light, the impact of the branching of alkyl-ether groups on the electronic properties was investigated via the synthesis of non-peripheral ([Formula: see text]-substituted n-butyl (1), iso-butyl (2) and sec-butyl (3) 1,4,8,11,15,18,22,25-octabutoxyphthalocyanines, in conjunction with Co and Cu metal centers. From 1 to 3 the first and second ring-based oxidation potentials were decreased by 70 mV and 110 mV respectively both for Cu and Co-containing complexes; the UV-visible Q-band maxima only changed by 4-8 nm, consistent with the destabilization of both the HOMO and LUMO, as confirmed by TD-DFT calculations. The reversibility of both redox couples was improved via branching (3) for the Co complexes. All six complexes were structurally characterized, with varying levels and types of ring distortions. All molecules show 1-D supramolecular stacking, but for n-butoxy 1Co an intermolecular Co-O interaction aligns the molecular stacks, while for sec-butoxy 3Co only [Formula: see text]-[Formula: see text] stacking of the Pc-ring was present. Both 3Co and 3Cu were ring-oxidized at lower potentials than 1Co and 1Cu, and the increased steric bulk from the branched ether chains prevented the overlap of their N8C8 inner rings.