Design and synthesis of an axially chiral platinum(II) complex and its CPL properties in PMMA matrix

A pair of an axially chiral platinum(II) complex was synthesized via Sonogashira coupling and subsequent coordination of a pincer ligand to a precursor. The complex exhibited a broad absorption band ranging from 250 to 550 nm in the UV-vis spectrum, with TD-DFT calculations indicating mixed ligand-to-ligand charge transfer (LL'CT) and metal-to-ligand charge transfer (MLCT) character. Photoluminescence measurements in CH₂Cl₂ solution revealed dual emission peaks at 427 nm and 596 nm, with a quantum yield of 3%. In PMMA matrix, the emission peaks were blue-shifted to 408 nm and 558 nm, and the quantum yield slightly increased to 4%. CD spectra showed distinct Cotton effects in the MLCT region, and CPL signals were observed only in the PMMA matrices, with a dissymmetry factor |<i>g</i> _lum| = 0.4 × 10^-3. These results demonstrate that axial chirality of the binaphthyl moiety governs the three-dimensional chiral arrangement of two platinum(II) chromophore units, leading to the chiroptical properties in the MLCT region through exciton coupling under restricted molecular motion.