NIR-II Emission from Cyclometalated Dinuclear Pt(III) Complexes

Half-lantern Pt (II) dinuclear complexes Pt (C∧Npz) (μ-S∧NR) 2 (HC∧Npz = 1-naphthalen-2-yl-1H-pyrazole; R = H, HS∧N: 2-mercaptopyrimidine 1; R = CF3, HS∧NF: 4- (trifluoromethyl) -2-mercaptopyrimidine 2) were selectively obtained as single isomers with the C∧N groups in an anti-arrangement and rather short metallophilic interactions (dPt–Pt = 2. 8684 (2) Å for 2). They reacted with haloforms in the air and sunlight to obtain the corresponding oxidized diplatinum (III) derivatives Pt (C∧Npz) (μ-S∧NR) X2 (X = Cl (1-Cl), Br (1-Br), I (1-I, 2-I) ). The single-crystal X-ray structures exhibit Pt–Pt distances typical for the existence of a metal–metal bond, which evidence fairly well the influence of the axial ligand (X). The reactions of 1 and 2 with CHI3 in the dark afforded mixtures of IPt (C∧Npz) (μ-S∧N) 2Pt (C∧Npz) CHI2 and 1-I or 2-I, with the former being the major species under an Ar atmosphere, while the reactions of 1 with CHBr3 and CHCl3 need light to occur. These Pt2 (III, III) complexes display low-energy absorptions and emissions that strongly depend on the axial ligand. In the solid state, they show a broad NIR emission ranging from 985 to 1070 nm at RT that suffers a hypsochromic shift when cooling down to 77 K. The photoemissive behavior of the dinuclear Pt (II) and Pt (III) systems is disclosed with the aid of density functional theory calculations.