Insight into the Heavy Atom Effect Induced by Environmental Heavy Atoms for Gadolinium-Labeled Hematoporphyrin Monomethyl Ether.

Environmental heavy atoms can further enhance the room temperature phosphorescence (RTP) emissions of gadolinium-labeled hematoporphyrin monomethyl ether (Gd-HMME) by way of the external heavy atom effect (HAE). However, the macroscopic phosphorescence intensity covered the intrinsic effect of the environmental heavy atoms. In this study, a method of separating the external HAE from the total is performed, and a quantity to describe the intrinsic nature of external HAE is defined. The environmental Gd 3+ concentration evolution of the phosphorescent transition rate ( k P ) is obtained by correlated absorption, emission, and time-resolved spectroscopy. The k P increases linearly with environmental Gd 3+ concentration, while the intercept k P0 coincides with that of the internal HAE. The slope κ could be calculated, and it is a quantity free of the Gd 3+ concentration and only relies on the type of environmental heavy atoms. In addition, the environmental Lu 3+ exhibits similar functionality to Gd 3+ in external HAE. Environmental Pd 2+ quenches the phosphorescence intensity macroscopically, while it enhances the HAE intrinsically. Our method provides an alternative insight into the intrinsic nature of environmental heavy atoms.