Porphyrin free base phosphorescence

Abstract

The wavelength for heavy atom enhanced phosphorescence is unambiguously established by time resolved excitation spectra in 50% EPA and 50% ethyl iodide at 77 K for protoporphyrin (795 nm), mesoporphyrin (773 nm), octaethylporphin (768 nm), and porphin (785 nm). Excitation spectra also establish the phosphorescence wavelength of brominated protoporphyrin in EPA at 77 K to be 783 nm, with a quantum yield φ p ∼ 9 × 10 −4. Using laser excitation the phosphorescence quantum yields in EPA were found for protoporphyrin ( φ p ∼ 5 × 10 −5), mesoporphyrin ( φ p < 6 × 10 −5), and tetraphenylprophin ( φ p ∼ 2 × 10 −5). Tetraphenylporphin phosphorescence shows no heavy atom enhancement. Natural radiative lifetimes for phosphorescence of the various free bases are found to be 70 sec and higher.