Synthesis and Characterization of Electron Donor–Acceptor Platinum(II) Complexes Composed of N,N‑Diphenylpyridineamine and Triphenylamine Ligands

The synthesis and electronic properties of a series of platinum­(II) complexes composed of electron-donor and electron-acceptor components as potential photovoltaic materials is reported. The complexes are composed of triphenylamines (TPA) and pyridine-derivatized TPAs as the electron-donating components, and alkynyl derivatives of 2,1,3-benzothiadiazole and cyclopentadithiophenone as the electron acceptors. The complexes containing the pyridine-derivatized ligands were prepared to examine the effect that direct coordination of a heteroatom-modified TPA may have on the electronic properties of donor–acceptor (D–A) complexes. Four complexes composed of meta- and para- pyridine-derivatized TPAs were prepared, and their electronic properties were compared with three structurally similar complexes composed of TPA, as well as with purely organic D–A compounds. Data collected from UV–vis and cyclic voltammetry show minor differences on the properties of the complexes containing the pyridine-derivatized ligands when compared to the TPA analogs, exhibiting similar highest occupied molecular orbital–lowest unoccupied molecular orbital bandgaps ranging from 2.156 to 2.705 eV for the pyridine-derivatized complexes (6a,b and 7a,b), 2.038–2.320 eV for the TPA complexes (8a,b and 9a), 2.301 eV for organic molecule 10a, and 1.997 eV for 10b. All compounds are stable, exhibiting no decomposition in the solid indefinitely, and only minor decomposition in solution. All compounds were characterized by ¹H and ¹³C nuclear magnetic resonance, infrared spectroscopy, and electrospray mass spectrometry. All complexes were also characterized by ³¹P nuclear magnetic resonance and elemental analysis of CHN; determination of Ag content for 6a,b and 7a,b (carried through the synthetic steps) was determined by inductively coupled plasma optical emission spectrometry. The para-pyridine-derivatized complex of 2,1,3-benzothiadiazole (6a) was further characterized by X-ray crystallography as a AgNO₃ clathrate. X-ray quality crystals were grown from a solution of hexanes/CH₂Cl₂ and from diffusion of hexanes into a CH₂Cl₂ solution of the complex, providing a solvent-free crystal and a solvate of CH₂Cl₂, respectively.