Intermediate 3 for TaAA9 also shows the intense feature around 400 nm seen for 3 in the LsAA9 spectrum. However, an additional transition is also seen at higher energy: the two most intense peaks in Fig. (green spectrum, left) are at 342 nm (3.63 eV) and 395 nm (3.14 eV). An analysis of the major orbital contributions of these peaks show a large involvement of the histidyl. The main peak at 395 nm mainly involves transitions from orbitals of hydroxyl lone pair character to an orbital of π-character on the histidyl His1. The less intense peak at higher energies (342 nm) occurs due to ligand-to-metal charge transfer transitions including orbitals on the histidyl. Similar transitions can also be observed for the isomer 3 ′ , albeit with the two most intense peaks red-shifted to 348 nm (3.57 eV) and 406 nm (3.05 eV) for the triplet state and 384 nm (3.23 eV) and 416 nm (2.98 eV) for the open-shell singlet. Overall, the spectra of 3 and 3 ′ are quite similar.