Improved O2 sensing performance by modifying P–P ligand in [Cu(N–N)(P–P)] complex

Abstract

In this paper, a diamine ligand of 2-(5-phenyl-[1,3,4]oxadiazol-2-yl)-pyridine (OP) and its corresponding Cu(I) complex of [Cu(OP)(POP)]BF4 with bis(2-(diphenylphosphanyl)phenyl) ether (POP) as the phosphorous ligand are synthesized. Full characterization on [Cu(OP)(POP)]BF4, including NMR, elemental analysis and single crystal analysis, confirms its molecular identity. Upon photon excitation, the emission of [Cu(OP)(POP)]BF4 owns a long excited state lifetime of 42.92μs and shows a maximum at 570nm, under pure N2 atmosphere. Theoretical calculation on [Cu(OP)(POP)]BF4 single crystal suggests that the excited state has a triplet metal-to-ligand-charge-transfer character. By embedding [Cu(OP)(POP)]BF4 into a optical silica supporting matrix of MCM-41, the emission signal is found to be sensitive towards various oxygen concentrations, with a maximum sensitivity of 7.31 (sensitivity=luminescence intensity in O2 medium/luminescence intensity in N2 medium). This improved sensitivity value compared with literature values is attributed to the introduction of POP ligand, which can suppress the intermolecular aggravation between [Cu(OP)(POP)]BF4 molecules and favor the oxygen attack on [Cu(OP)(POP)]BF4 excited state. Due to the same reason, a short response time is also observed with stable quenching signal.