Time-resolved electron paramagnetic resonance study of rhodium(III) corroie excited states

Photoexcited states of three Rh(III) 5,10,15-tris(pentafluorophenyl) corroles coordinated by different axial ligands; namely, triphenylphosphine P(C₆H₅)₃ group (1), pyridine C ₆H₅N group (2), and two pyridine groups (3) were studied by X- and Q-band time-resolved electron paramagnetic resonance (TREPR) in frozen toluene and liquid crystal E-7. Transient mutations were utilized to identify multiplicity of the detected paramagnetic species. The spectra of 1 and 2 were assigned to triplet (³ππ*) states, while contributions of triplet (³dd and charge transfer ³CT) and quintet ( ⁵dd) states were revealed in the spectrum of 3. The results are interpreted in terms of a peculiar nature of transition metal complexes with the unfilled d-shell, where close lying electronic states of different multiplicities may be mixed through configurational, spin - orbit, and vibronic coupling. From the EPR spectra, the spin - orbit coupling constant was estimated to be about 25 cm^-1. It is shown that different axial ligation of complexes shifts the relative energy of the excited states and, consequently, leads to population of different states. Plausible explanations of the effects governing unusual spectral and dynamic parameters of the photoexcited Rh corrole complexes are presented.