Study on the synthesis, characterization, photophysical performance and oxygen-sensing behavior of a luminescent Cu(I) complex with large conjugation plane

In this paper, a diamine ligand of dipyrido[3,2-a:2′,3′-c]phenazine (DPPZ) and its corresponding Cu(I) complex with triphenylphosphine (PPh3) as the phosphorous ligand are synthesized. Full characterization on [Cu(DPPZ)(PPh3)2]BF4, including NMR, elemental analysis and single crystal analysis, confirms its molecular identity. Upon photon excitation, the emission of [Cu(DPPZ)(PPh3)2]BF4 owns a long excited state lifetime of ∼6 μs and shows a maximum intensity at 616 nm, under pure N2 atmosphere. Theoretical calculation on [Cu(DPPZ)(PPh3)2]BF4 single crystal suggests that the excited state has a triplet metal-to-ligand-charge-transfer character. By embedding [Cu(DPPZ)(PPh3)2]BF4 into a polymer supporting matrix of polystyrene, the emission signal is found to be sensitive towards varying oxygen concentrations, with a maximum sensitivity of 3.78. We attribute this sensitivity to the large conjugation plane in DPPZ ligand which can increase the population of excited state electrons and favor the oxygen attack on [Cu(DPPZ)(PPh3)2]BF4 excited state. Due to the porous structure of nanofibrous polystyrene matrix, a short response time of ∼16 s towards molecular oxygen is also observed with stable quenching signal.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We report a diamine ligand with large conjugation plane and its Cu(I) complex. ► Crystal structure, photophysical property and electronic nature were investigated. ► It owned a long excited state lifetime favoring oxygen-sensing. ► It was doped into a polymer matrix to construct composite nanofibers. ► A maximum sensitivity of 3.78 with short response time of 16 s was realized.