Spectroscopic and DFT studies of photoactivatable Mn(I) tricarbonyl complexes

A combined experimental study and density functional theory calculations of fac-[MnBr (CO)₃L] complexes (L = 2-(2′-pyridyl)benzimidazole ligand, furnished with either morpholine (L^morph) or phthalimido (L^phth) side-chain) were performed using different spectral and analytical tools. The synthesized complexes released carbon monoxide upon the exposure to LED source light at 468 nm. Illumination of fac-[MnBr (CO)₃L] (10 μM) in the myoglobin solution (Mb) produced about 25 μM MbCO. The plateau of the CO release process is attained within 25 min. With the aid of time-dependent density functional theory calculations, the observed lowest energy absorption transition at ~ 400 nm has a ground-state composed of d (Mn)/π (pyridyl) and excited-state of ligand π*-orbitals forming MLCT/π-π^*. Natural population analyses of fac-[MnBr (CO)₃L] were carried out to get information about the strength of Mn–CO bonds, electronic arrangment and natural charge of manganese ion.