Visible Light–Excited Pt(II) Acetylide Complexes Bearing red Emission: Synthesis, Characterization, X‐Ray Structure Analysis, Photoluminescence, and TD‐DFT Investigations

The advancement of visible-light harvesting Pt(II) complexes with extended excited state lifetimes is crucial, as these properties are essential for their applications in photocatalysis, nonlinear optics, photodynamic therapy, among other areas. In this study, we synthesized platinum complexes with main ligands bearing sulfur (S) donor atoms, which not only shifted the absorption into the visible range but also increased the excited state lifetimes in solution as well as in solid state. In this context, two series of platinum complexes (C1a–C6a and C1b–C6b) were synthesized in excellent isolated yields in a single step reaction catalyzed by CuI in the presence of base from precursor complexes (PC1a–PC6a and PC1b–PC6b) bearing chloride ancillary ligand. These complexes were characterized by multiple analytical techniques, among them five complexes (C1a, C5a, C6a, C2b, and C6b) were analyzed in solid state by single crystal X-ray analysis that showed the exact orientation of the ligands around Pt and intramolecular/intermolecular bonding in these complexes. The solid-state structure demonstrated dimeric structures interacting through noncovalent π⋯π stacking that could be responsible for extended lifetime, longer wavelength emission, and phosphorescence. These complexes absorbed mainly around 240 to 260 and 420 to 500-nm visible region assigned to ligand–ligand charge transfer (LLCT) and metal-to-ligand charge transfer (MLCT), respectively. The photoluminescence was observed in 630-nm region when excited at 450-nm visible wavelength in both solution and solid state. The absorption and emission properties of all these complexes were further investigated by time-dependent density functional theory (TD-DFT) calculations that rationalized the effect of different constituents on the main SNO donor ligand. The strong absorption in the visible region and emission in the near-infrared (NIR) region in both solid and solution state suggested that these complexes could have potential applications in various fields of optoelectronics, materials science, and photodynamic therapy.