Porphyrins. XXXII. Absorptions and luminescence of Cr(III) complexes

Chloro−(tetraphenylporphinato)chromium(III) shows relatively normal visible (Q) bands in the region 610−500 nm and a relatively normal Soret (B) band at 447 nm; in addition, there are prominent bands in the near uv region 400−300 nm (2×104 < ε < 3×104 M−1⋅cm−1) and clear near ir bands in the region 820−610 nm (300 < ε < 2100 M−1⋅cm−1). At 160°K there is one main emission band at ∼815nm (τ < 6 μsec); at 77°K there are emission bands of comparable intensity at both 811 and 847 nm (τ = 44 μsec); at 4°K both emission bands appear with intensity ratio I811/I847 = 0.12. The near ir absorption and emission band at 811 nm is attributed to a ’’trip−quartet’’ excited state formed from the (π,π*), S = 1 porphyrin state coupling to the d3, S = 3/2 electrons of the Cr(III); the 847 nm emission is attributed to the sextet state that arises from the same electron configuration. The prominent near uv bands are attributed to a2u(π), a1u(π) → eg(dπ) charge transfer transitions. Phenol−phenoxo− (octaethylporphinato)chromium(III) shows similar absorption and emission spectra, but the bands are generally blue shifted.