Synthesis and characterization of the axially ferrocenyl substituted subphthalocyanines

Abstract

Two new ferrocenyl-subphthalocyanine dyads with ferrocenenylmethoxide (2) and ferrocenyl carboxylate (3) substituents directly attached to the subphthalocyanine ligand via the axial position have been prepared and characterized using NMR, UV-vis, and MCD spectroscopies as well as X-ray crystallography. Redox properties of the ferrocenyl-containing dyads 2 and 3 were investigated using the cyclic voltammetry (CV) approach and compared to those in parent subphthalocyanine 1. CV data reveal that the first reversible oxidation is ferrocene-centered, while the second oxidation and the first reduction are localized on the subphthalocyanine ligand. The electronic structures and the nature of the optical bands observed in UV-vis and MCD spectra of all target compounds were investigated by DFT-PCM and TDDFT-PCM approaches. It has been found that in both dyads 2 and 3 HOMO to HOMO-2 are ferrocene-centered MOs, while HOMO-3 as well as LUMO and LUMO+1 are localized on the subphthalocyanine ligand. Fluorescence properties of the dyads 2 and 3 were investigated using steady-state and time-resolved fluorescence methods. It has been found that the fluorescence quenching is more efficient in dyad 3 as compared to dyad 2, which was rationalized on the basis of DFT-PCM calculations. Similar tert-butyl SubPc compounds 4 and 5 were synthesized and characterized by UV-Vis, MCD, NMR, Fluorescence and electrochemical methods to determine the effects the tert-butyl groups has on the solubility of SubPc. UV-Vis and MCD show a slight shift in the Q-band to about 570 nm from about 564 nm of that of compounds 1-3. Fluorescent intensities of compounds 4 and 5 were measured under similar conditions and it was found that the addition of ferrocene carboxylate again quenches the emission. CV data for compound 5 suggests that there is a first reversible oxidation process centered on ferrocene. There are also two irreversible processes belonging to SubPc. Finally, the more electron dense, thiol substituted SubPc compound 10 was synthesized and characterized using UV-Vis, MCD, NMR, Fluorescence and electrochemical methods. Because of the additional electron density there was a shift of 80 nm to lower energy from 564 nm in compound 1 for the Q-band in the UV-Vis spectrum. Similarly, the fluorescent spectrum has a shift of 80 nm and is a mirror image of the Q-band. Finally, CV methods show agreement with compounds 1-5, that there is an irreversible oxidation and reduction peak belonging to that of the subphthalocyanine core at 0.6987V and -1.893V respectively. The first oxidation process at 0.3943 V however is a reversible process that has not been seen in compounds 1 & 4. It is possible that it belongs to another process of the compound that is only introduced with the thiol substituents. This can be responsible for the first irreversible reduction process at -1.5063 V as well.