Excellent capacity of singlet oxygen generation by gadolinium labelled sinoporphyrin sodium

Abstract The singlet oxygen quantum yield (ΦΔ) represents the ability of a photosensitizer to produce the photodynamic therapy effect. However, the pursuiting of strong phosphorescence properties of metalloporphyrins hindered the fact that they may have high ΦΔ. In this paper, we studied the effect of imidazole, a small organic molecule used as a solvent in the synthesis of multifunctional photosensitizers (PSs), on the ΦΔ of the PS, gadolinium-containing sinoporphyrin sodium (Gd-DVDMS), using a relative method with Rose Bengal as the reference and 1,3-diphenylisobenzofuran as the singlet oxygen trapping reagent. After completely removal of imidazole by dialysis, the ΦΔ value of Gd-DVDMS was obtained to be as high as 0.97. In addition, with an increase in the imidazole concentration, the ΦΔ of Gd-DVDMS gradually decreased, and stabilized at a value of 0.37. To understand the above phenomenon, the ultraviolet–visible absorption and photoluminescence spectra of Gd-DVDMS for different imidazole concentrations were analyzed. The triplet state quantum yield of Gd-DVDMS was constant, while the O2 quenching rate of the triplet state decreased; this indicated that the energy exchange between the PS and O2 was reduced by imidazole. We deduced that decrease in ΦΔ was attributable to the increase in the distance between Gd-DVDMS and O2, owing to imidazole wrapping around Gd-DVDMS. It is speculated that as the wrapping progressed, the effects of the dissolution and attachment of imidazole reached a balance, and hence, the ΦΔ remained constant.