Enhancement of the room temperature phosphorescence of metalloporphyrins using imidazole as a triplet state protector

Abstract

The enhancement of the room-temperature phosphorescence (RTP) emissions of phosphorescent metalloporphyrins is critical toward extending their applications in many fields. Imidazole is widely used as a molten solvent in the synthesis of metalloporphyrins and can influence their RTP emissions. Here, the effects of imidazole on the RTP emissions of a series of metalloporphyrins (hematoporphyrin monomethyl ether coordinated to gadolinium (Gd-HMME), lutetium (Lu-HMME), and palladium (Pd-HMME) ions) were studied. It was found that imidazole effectively enhanced the RTP emissions of these metalloporphyrins both on a solid matrix and in solution. For metalloporphyrins on a solid matrix (filter paper), the RTP intensities of samples immersed in an imidazole solution were much higher than those immersed in methanol. Imidazole enhanced the phosphorescence quantum yields (ΦP) of Gd-, Lu- and Pd-HMME on filter paper by 23-, 5.0-, and 3.5-fold, respectively. For metalloporphyrins in solution (methanol), the RTP intensities increased gradually with the concentration of imidazole. These results indicate that imidazole has potential as an RTP enhancer by protecting the triplet states of phosphorescent metalloporphyrins.