Excited state vibrational spectroscopy of metal complexes of dipyrido[3,2-a:2′,3′-c]phenazine

The use of vibrational spectroscopic methods to elucidate the states present in metal complexes of dipyrido3,2-a:2,3-c]phenazine (dppz) are reviewed. The presence of the close lying b₁(ψ) and b₁(phz) molecular orbitals leads to a number of close lying intraligand and MLCT excited states. Using resonance Raman spectroscopy the nature of initial photoexcitation may be established as M→b₁(ψ). For Ru(II) complexes the lowest excited state is ³MLCT(phz) in nature. However, for Re(CO)₃Cl] complexes the relaxation from the initial excited state may lead to population of a ³MLCT(phen), ³MLCT(phz) state, an state, or an equilibrium between these states. Time-resolved resonance Raman spectroscopy may be used to identify the presence of dppz^·- or the state and has also been used to identify features associated with intercalation of dppz complexes with DNA. The Raman methods are less effective at detecting the short time dynamics between these states. However, this may be accomplished using time-resolved infrared spectroscopy in which all three states may be unambiguously determined. The clearest picture of the dynamics in dppz complexes has been achieved by using a combination of time-resolved resonance Raman, time-resolved infrared and DFT calculations for rhenium(I) complexes.