Monitoring this reaction by UV-vis spectroscopy at -20°C (Figure ) clearly showed a gradual conversion of the starting metallocavitand 8 into the corresponding Mn-oxo species 9, which exhibited a prominent absorption band centered at λmax = 507 nm. This finding was somewhat surprising, as characteristic absorption bands of the reported Mn(IV)-oxo species typically occur at significantly longer wavelengths (700-1000 nm). Therefore, to gain an insight into the origin of this unexpected absorption band, we performed a time-dependent DFT (TDDFT) study on a model Mn(IV)-oxo complex 9*, simplified similarly to 8* (see SI for details). The computational results indeed predicted an electronic transition with the biggest oscillatory strength to occur at 485 nm (Figure ), in a good agreement with the observed spectrum. A detailed examination of the electronic states involved in this transition identified its two major constituents as HOMO(α)→LUMO+2(α) (60%) and HOMO-2(α)→LUMO+2(α) (24%). Inspection of the corresponding molecular orbitals (Figure ) revealed that while the LUMO+2(α) acceptor orbital is an antibonding σ* orbital, with a predominantly metal character (56% Mn 𝑑 𝑥 2 -𝑦 2 ), only the HOMO-2(α) donor orbital has a significant contribution from the metal-oxo moiety (17% Mn 𝑑 𝑥𝑧 and 63% Ooxo 𝑝 𝑧 ). The other donor orbital, HOMO(α) -which is the major contributor to the transition -is predominantly localized on the phenolate rings of the cavitand (exhibiting a π* antibonding character) and has only a minor contribution from the metal-oxo moiety. Thus, the electronic transition which gives rise to the absorption at 507 nm can be best described as a ligand-to-metal charge transfer (LMCT). This assignment is also supported by the high intensity of this absorption band (ε = 2,600 L•mol -1 cm -1 ), in consistency with other metalphenolate complexes. In fact, two lower energy Laporteforbidden d-d transitions (at 735 and 785 nm) similar to the reported Mn(IV)-oxos were also predicted by our TDDFT calculations. However, due to their significantly lower intensity compared to the LMCT transition, the corresponding absorption bands could not be resolved in the spectrum.