LAUSR

Abstract Gd(III)-porphyrins are promising phosphorescent materials that are widely available and inexpensive compared to the most widely used phosphorescent materials (e.g., Pt(II)- and Pd(II)-porphyrins). However, Gd(III)-porphyrins are generally unstable in aqueous solutions, which limits their application in the biomedical field. Here, we report a method for stabilizing gadolinium-hematoporphyrin monomethyl ether (Gd-HMME), a Gd(III)-porphyrin, in aqueous solutions using the tripodal (cyclopentadienyl)tris(dimethylphosphito)cobaltate(I) anion, (LOMe–). When not complexed with LOMe–, the luminescence and UV–visible spectra of Gd-HMME in an aqueous solution show the luminescence and absorption characteristics of HMME after several hours of storage. However, after binding with LOMe–, the luminescence and absorption spectra of Gd-HMME-LOMe show no obvious change even after several days of storage in the aqueous solution. Gd-HMME-LOMe can be stored in aqueous solutions for longer than one month, which is sufficient for practical use. The phosphorescence intensity of Gd-HMME-LOMe decreased with increasing oxygen concentration, while its fluorescence intensity remained unchanged, indicating that Gd-HMME-LOMe can be used as a ratiometric oxygen sensor. In the investigated oxygen concentration range, the Stern–Volmer plot exhibits an appropriate linear, with a response factor greater than 10, which is sufficiently high for practical oxygen sensing. Thus, a Gd-porphyrin complex with ratiometric oxygen-sensing ability, which is stable in aqueous solution, was prepared in this study.