Excited-state dynamics of [Mn(im)(CO)3(phen)]+: PhotoCORM, catalyst, luminescent probe?

Mn(I) alpha -diimine carbonyl complexes have shown promise in the development of luminescent CO release materials (photoCORMs) for diagnostic and medical applications due to their ability to balance the energy of the low-lying metal-to-ligand charge transfer (MLCT) and metal-centered (MC) states. In this work, the excited state dynamics of [Mn(im)(CO)(3)(phen)](+) (im = imidazole; phen = 1,10-phenanthroline) is investigated by means of wavepacket propagation on the potential energy surfaces associated with the 11 low-lying S-n singlet excited states within a vibronic coupling model in a (quasi)-diabatic representation including 16 nuclear degrees of freedom. The results show that the early time photophysics (<400 fs) is controlled by the interaction between two MC dissociative states, namely, S-5 and S-11, with the lowest S-1-S-3 MLCT bound states. In particular, the presence of S-1/S-5 and S-2/S-11 crossings within the diabatic picture along the Mn-COaxial dissociative coordinate (q(Mn-COaxial)) favors a two-stepwise population of the dissociative states, at about 60-70 fs (S-11) and 160-180 fs (S-5), which reaches about 10% within 200 fs. The one-dimensional reduced densities associated with the dissociative states along q(Mn-COaxial) as a function of time clearly point to concurrent primary processes, namely, CO release vs entrapping into the S-1 and S-2 potential wells of the lowest luminescent MLCT states within 400 fs, characteristics of luminescent photoCORM.

Automated summary

Mn(I) alpha-diimine carbonyl complexes show promise in the development of luminescent CO release materials for diagnostic and medical applications due to their ability to balance the energy of low-lying metal-to-ligand charge transfer and metal-centered states. The excited state dynamics of [Mn(im)(CO)(3)(phen)](+) reveal that early time photophysics is controlled by the interaction between two MC dissociative states, S-5 and S-11, with the lowest MLCT bound states, leading to a two-stepwise population of dissociative states favoring CO release vs entrapping within the lowest luminescent MLCT states.