The spectroscopic properties and photochemistry of the complexes Mn(R) (CO) 3 (R'-DAB) (R = Me, Bz; R' = iPr, pTol) are reported. The UV-photoelectron spectrum of Mn(Me) (CO) 3 (iPr-DAB) shows that the σ(Mn-Me) orbital has a higher ionization potential than the d π (Mn) orbitals, which is of importance for the photochemical behavior of this complex. The R group bound to the metal determines the photochemistry of these complexes. The Me complexes lose CO upon irradiation into their MLCT bands. The CO-loss products react with Lewis bases, the final product being cis(CO,CO),trans(Me,L)-Mn(Me) (L) (CO) 2 (R'-DAB). The structure of one of these products, viz.cis,trans -Mn(Me) (P(OMe) 3 ) (CO) 2 (iPr-DAB) (C 1 4 H 2 8 N 2 O 5 PMn) has been determined by a single-crystal X-ray diffraction study (T = 200 K). The crystal is monoclinic, space group P2 1 n with unit cell dimensions a = 15.435(3),b = 15.200(3), c = 18.192(4) a, V = 3915(2) a 3 , Z = 8. The structure refinement converged to R = 0.077 for 2829 observed reflections (total number of parameters: 319). Transient absorption spectroscopy shows that an equatorial CO ligand is lost upon excitation and that the final product is formed via differentcis,cis -isomers. For R = Bz, visible excitation leads to efficient homolysis (Φ = 0.4 for R' = iPr) of the Mn-Bz bond, resulting in the formation of radicals which are characterized by ESR spectroscopy. The different behavior of the Bz and Me complexes is attributed to a difference in relative energies of two reactive excited states. For R = Me, the complexes lose CO from the lowest MLCT state; for R = Bz they undergo homolysis of the Mn-Bz bond from the lowest σπ * state.