Picosecond Spectroscopy and Kinetics of Metalloporphyrins

Picosecond transient Spectroscopy has been used to measure excited state lifetimes ancfrspectra of Cr, Mn, Fe, Sn and Pb meso-tetraphenylporphyrins. Excited state spectra are typical of π,π^* states, and lifetimes vary from > 20 ns in Cr(III) tetraphenylporphyrin to 8 ps in Mn(II). This contrasting behaviour in the transition metal porphyrins is interpreted as being due to charge transfer states lying above the initially excited states in Cr but below those in Mn and Fe, as recently predicted by theory. Only in Sn(IV) tetraphenylporphyrin was the singlet-singlet absorption spectrum measurable; the excited singlet state lifetimes for the other porphyrins were < 1 ps.