Improving oxygen sensing performance via inner-molecular π-π stacking in a series of phosphorescent Cu(I) complexes

Article abstract of DOI:10.1016/j.saa.2020.118537

In this paper, six phosphorescent Cu(I) complexes with three diamine ligands and two phosphorous ligands were prepared. Detailed discussion was performed on these complexes, including single crystals, quantum mechanics theoretical calculation, absorption spectra, emission spectra, emission quantum yields and excited state decay dynamics. Large conjugation planes and π-π stacking were found in these complexes. Their emission was originated from MLCT excited state. Long-lived emissive center was observed due to this MLCT-based decay and the help from π-π stacking. Such long-lived emissive state and the large conjugation planes in these complexes offered enough collision probability with O₂ molecules, making themselves potential oxygen sensing probes. These six complexes were then doped into silica supporting matrix MCM-41 spheres. The resulting composite samples and their emission sensing response towards O₂ were discussed in detail. The optimal sample showed sensitivity as high as 7.80 with response time of 14 s. A careful discussion between Cu(I) complex molecular structure and sensing performance was performed. It was concluded that both a long lifetime and a large conjugation plane lead to improved sensing sensitivity since they increased the collision probability with O₂ molecules. On the other hand, it was found that both sensing response and recovery times were mainly controlled by O₂ diffusion in supporting matrix.