Photoinduced Charge Transfer in Short-Distance Ferrocenylsubphthalocyanine Dyads

Two new ferrocenylsubphthalocyanine dyads with ferrocenylmethoxide
(2) and ferrocenecarboxylate (3) substituents
directly attached to the subphthalocyanine ligand via the axial position
have been prepared and characterized using NMR, UV–vis, and
magnetic circular dichroism (MCD) spectroscopies as well as X-ray
crystallography. The redox properties of the ferrocenyl-containing
dyads 2 and 3 were investigated using the
cyclic voltammetry (CV) approach and compared to those of the 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 nature of the optical bands observed in
the UV–vis and MCD spectra of all target compounds were investigated
by a density functional theory polarized continuum model (DFT-PCM)
and time-dependent (TD)­DFT-PCM approaches. It has been found that
in both dyads the highest occupied molecular orbital (HOMO) to HOMO–2
are ferrocene-centered molecular orbitals, while HOMO–3 as
well as lowest unoccupied molecular orbital (LUMO) and LUMO+1 are
localized on the subphthalocyanine ligand. TDDFT-PCM data
on complexes 1–3 are consistent with
the experimental observations, which indicate the dominance of π–π*
transitions in the UV–vis spectra of 1–3. The excited-state dynamics of the dyads 2 and 3 were investigated using time-correlated single photon counting,
which indicates that fluorescence quenching is more efficient in dyad 3 compared to dyad 2. These fluorescence lifetime
measurements were interpreted on the basis of DFT-PCM calculations.