Electrochemistry, Chemical Reactivity, and Time-Resolved Infrared Spectroscopy of Donor–Acceptor Systems [(Q(x))Pt(pap(y))] (Q = Substituted o-Quinone or o-Iminoquinone; pap = Phenylazopyridine)

[Image: see text] The donor–acceptor complex [((O,N)Q(2–))Pt(pap(0))] (1; pap = phenylazopyridine, (O,N)Q(0) = 4,6-di-tert-butyl-N-phenyl-o-iminobenzoquinone), which displays strong π-bonding interactions and shows strong absorption in the near-IR region, has been investigated with respect to its redox-induced reactivity and electrochemical and excited-state properties. The one-electron-oxidized product [((O,N)Q(•–))Pt(pap(0))](BF(4)) ([1]BF(4)) was chemically isolated. Single-crystal X-ray diffraction studies establish the iminosemiquinone form of (O,N)Q in [1](+). Simulation of the cyclic voltammograms of 1 recorded in the presence of PPh(3) elucidates the mechanism and delivers relevant thermodynamic and kinetic parameters for the redox-induced reaction with PPh(3). The thermodynamically stable product of this reaction, complex [((O,N)Q(•–)) Pt(PPh(3))(2)](PF(6)) ([2]PF(6)), was isolated and characterized by X-ray crystallography, electrochemistry, and electron paramagnetic resonance spectroscopy. Picosecond time-resolved infrared spectroscopic studies on complex 1b (one of the positional isomers of 1) and its analogue [((O,O)Q(2–))Pt(pap(0))] (3; (O,O)Q = 3,5-di-tert-butyl-o-benzoquinone) provided insight into the excited-state dynamics and revealed that the nature of the lowest excited state in the amidophenolate complex 1b is primarily diimine-ligand-based, while it is predominantly an interligand charge-transfer state in the case of 3. Density functional theory calculations on [1](n+) provided further insight into the nature of the frontier orbitals of various redox forms and vibrational mode assignments. We discuss the mechanistic details of the newly established redox-induced reactivity of 1 with electron donors and propose a mechanism for this process.