Mono and binuclear Pt(II) complexes incorporated with NHC ligands: syntheses, photophysical properties, and acid vapor responses

Abstract

Three mononuclear complexes (PtL1H, PtL2H, and PtL3H) and one binuclear complex (Pt₂L1) have here been prepared using the bis-carbene ligand of 1,3-propylene-bis(1,3-dihydro-3-butyl-2H-imidazol-2-ylidene) and one of three rigid planar ligands of dibenzo[f,h]quinoxaline (L1H₂), dibenzo[a,c]phenazine (L2H₂), and tribenzo[a,c,i]phenazine (L3H₂). These four complexes were fully characterized by nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HRMS), and elemental analyses. Moreover, the two binuclear complexes Pt₂L2 and Pt₂L3 could not be isolated, but Pt₂L3 was isolated and characterized by single-crystal X-ray diffraction (XRD). Complexes PtL1H, PtL2H, and Pt₂L1 exhibited phosphorescence in N₂-degassed dichloromethane (DCM) solution at 563 nm, 656 nm, and 624 nm, respectively. Also, Pt₂L1 exhibited triplet emission at 553 nm in a 2 wt% PMMA film, with the highest Ф of 63 % and τ of 23.8 μs. Moreover, complexes PtL1H and Pt₂L1 were deposited on quartz plates to monitor formic acid vapor and acetic acid vapor. The plates that were covered with PtL1H exhibited phosphorescent quenching in both formic acid and acetic acid. However, the plates that were covered with Pt₂L1 did only show a prompt response to formic acid, but were not sensitive to acetic acid.