The electronic absorption spectrum of fac-[Mn(CO)3(phen)imH]+, fac-1 in CH2Cl2 is characterized by a strong absorption band at 378 nm (εmax = 3200 mol−1 L cm−1). On the basis of quantum mechanical calculations, the visible absorption band has been assigned to ligand-to-ligand charge-transfer (LLCT, im→phen) and metal-to-ligand charge-transfer (MLCT, Mn→phen) charge transfer transition. When fac-1 in CH2Cl2 is irradiated with 350 nm continuous light, the absorption features are gradually shifted to represent those of the meridional complex mer-[Mn(CO)3(phen)imH]+, mer-1 (λmax = 556 nm).
The net photoreaction under these conditions is a photoisomerization, although, the presence of the long-lived radical species was also detected by 1H NMR and FTIR spectroscopy. 355 nm continuous photolysis of fac-1 in CH3CN solution also gives the long-lived intermediate which is readly trapped by metylviologen (MV2+) giving rise to the formation of the one-electron reduced methyl viologen (MV•+). The UV−vis spectra monitored during the slow (45 min) thermal back reaction exhibited isosbestic conversion at 426 nm. On the basis of spectroscopic techniques and quantum mechanical calculations, the role of the radicals produced is analyzed.
de Aguiar, I., Inglez, S.D., Lima, F.C., Daniel, J.F., McGarvey, B.R., Tedesco, A.C. and Carlos, R.M., 2008. Photochemical reactions of fac-[Mn (CO) 3 (phen) imidazole]+: evidence for long-lived radical species intermediates. Inorganic chemistry, 47(24), pp.11519-11526.
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