Synthesis, Structure, and Optical Properties of the Platinum(II) Complexes of Indaphyrin and Thiaindaphyrin

The novel free base meso-di(5′-methylthien-2′-yl)thiaindaphyrin, 10, was prepared from the corresponding meso-tetra(thien-2-yl)porphyrin using a methodology analogous to that for the preparation of known meso-diphenylindaphyrin, 5: β,β′-Dihydroxylation of the porphyrin is followed by oxidative diol cleavage. The resulting aldehyde moieties undergo an acid-catalyzed intramolecular Friedel−Crafts alkylation of the adjacent meso-thienyl groups with concomitant oxidation. Insertion of Pt(II) into either of the chromophores is facile, producing 5Pt and 10Pt. The crystal structure of 5Pt, the first for any indaphyrin, shows that the conformation of the indaphyrinato ligand is strongly ruffled, while the N4 donor set that coordinates the central Pt(II) maintains a near-perfect square-planar coordination geometry around the central metal ion (crystal data for C44H24N4O2Pt: triclinic space group P1̅ with a = 8.8735(4) Å, b = 12.9285(6) Å, c = 14.3297(6) Å, α = 88.785(1)°, β = 82.248(1)°, γ = 72.422(1)°; Z = 2). The UV−vis and emission spectra, triplet yields, and lifetimes of the Pt(II) complexes 5Pt and 10Pt were determined. Both complexes luminesce (in EtOH at 77 K) in the NIR (5Pt: λmax-emission = 864, 974 nm, lifetime 2 μs; 10Pt: λmax-emission = 990, 1112, 1276 nm) with modest to low quantum yields (Φp ∼ 1% and ∼ 6 × 10−3 %, respectively).