Platinum Complexes from C–H Activation of Sterically Hindered [C^N] Donor Benzothiophene Imine Ligands: Synthesis and Photophysical Properties

Abstract

Primary amines and benzothiophene-3-carboxaldehyde were reacted to give four large, bulky imine ligands. These imine ligands were reacted with a tetramethyl platinum dimer and by heteroatom-assisted C–H activation, both monometalated compounds and bismetalated compounds were synthesized. In all cases, five-membered platinacycles were formed. The compounds were characterized by NMR spectroscopy, and one bismetalated compound was characterized by single-crystal X-ray diffraction. The UV–vis absorption and emission spectra and the excited-state lifetimes were recorded for these complexes. Density functional theory (DFT) and time-dependent-DFT calculations were performed to aid in the assignment of the absorption and emission spectra of the newly synthesized complexes.

Photophysical Properties of Cyclometalated Platinum(II) Diphosphine Compounds in the Solid State and in PMMA Films

“…[Pt­(dmso) 2 Cl 2 ] was synthesized according to a previously published procedure , according to a modification of known procedures and can be found in the Supporting Information.…”

“…The 1 H NMR characterization relied heavily on the diagnostic methylene and imine peaks 32 of the chelated L1 ligand 10 and on the alkyl chain protons of the various bis(diphenylphosphino) ligands. For example, the 1 H NMR of L1-DPPM clearly displayed the imine resonance as a doublet at 8.90 ppm ( 3 J Pt-H = 44 Hz, 3 J H-P = 9 Hz), the methylene of L1 as a singlet at 5.33 ppm ( 3 J Pt-H = 14 Hz), and the methylene of the bis(diphenylphosphino)methane as a triplet at 5.12 ppm ( 3 J Pt-H = 40 Hz, 3 J Pt-P = 21 Hz).…”

“…Phosphorescent organometallic complexes have application potential in devices due to their tunable and efficient luminescent properties. − Due to these complexes’ emissive properties, they are widely studied for their application in fields such as bioimaging, chemical sensors, organic light-emitting diodes, and light-emitting electrochemical cells. − Specifically, the photoluminescent properties of organometallic Pt­(II) complexes have been reported and widely studied. − The luminescent properties of these complexes are likely due to the presence of strong carbon donors, the inclusion of aromatic rings, and the large spin-orbit coupling of the heavy metal platinum center. ,, Additionally, the photophysical properties of Pt­(II) complexes can be tuned by altering the ligand environment of the coordination compound, including changes to cyclometalated ligands and/or the auxiliary ligands. ,, …”

Synthesis, Structure, and Photophysical Properties of Platinum Compounds with Thiophene-Derived Cyclohexyl Diimine Ligands

“…In this work, we explore a new type of cyclohexyl diimine C^N^N ligand featuring a thiophene ring, as is shown in Scheme . Conjugated thiophene polymers and oligomers are attractive organic optoelectronic materials in their own right, − and metal complexes featuring metalated or pendant thiophenes with interesting photophysical properties have been reported. − In particular, metalated thiophenes as compared to phenyl groups in structurally analogous Pt­(II) complexes have been reported to enhance fluorescence over phosphorescence in recent studies. , Among aromatic rings, thiophenes have been reported to be reactive toward C–H activation and are excellent candidates for preparing cyclometated complexes through C–H activation reactions. , Using this diimine C^N^N ligand framework, we report the synthesis, structural characterization, and photophysical properties of new Pt­(II)/Pt­(IV) complexes and have compared their properties with the structurally related benzene-derived complexes reported earlier by Puddephatt. , We report their luminescence in both solution and solid media for these four complexes, as a major focus of recent research in luminescent inorganic complexes is the impact of physical state and intermolecular order on photophysical properties. − …”