The excited-state dynamics, luminescence, and redox properties of a series of hexanuclear molybdenum cluster complexes, (nBu₄N)₂[Mo₆X₁₄] and (nBu₄N)₂[Mo₆X₈(CF₃COO)₆] (X = Cl, Br, or I), were investigated. Substitution of the apical halogen ligands for the trifluoroacetate ligands increased the oxidation potentials and induced a blue shift in the absorption and luminescence bands as well as a considerable increase in the luminescence quantum yields for heavy inner ligands. Time-resolved transient absorption measurements showed that the intersystem crossing from the excited singlet states is ultrafast with time constants ranging between <120 fs and 1.68 ps and leads to hot triplet states. The following cooling occurred at a ps time scale and was assigned to electronic redistribution within the emissive triplet state sublevels. The formation of singlet oxygen, O₂(¹Δ_g), suggested earlier on the basis of photooxidation experiments for some complexes, was revised by direct measurements of O₂(¹Δ_g) phosphorescence. We showed the effects of the attached ligands on key physico-chemical and photophysical parameters of the title complexes. The synthesis and structural characterisation of a new cluster complex, (nBu₄N)₂[Mo₆Br₈(CF₃COO)₆], completed the series. Our results demonstrated that the complexes with heavy inner ligands (Br, I) and apical trifluoroacetate ligands were photochemically and electrochemically stable, highly luminescent, and good sensitisers of O₂(¹Δ_g).

Newly synthesized zinc phthalocyanine bearing sixteen quaternized imidazolyl moieties on the periphery displays high water-solubility, lack of aggregation and high singlet oxygen quantum yield in water (Φ_Δ > 0.33). The in vitro tests indicated excellent anticancer photodynamic activity (EC₅₀ = 36.7 nM) and low dark toxicity to non-cancerous cells (TC₅₀ = 395 μM).