Additional spectroscopic studies are clearly warranted, of which NMR spectroscopy and nitrogen 1s X-ray photoelectron spectroscopy seem particularly promising. The latter technique has shed substantial light on the charge asymmetry of low-barrier hydrogen bonds in porphycenes. 20 . Like other free-base corroles, H3Cor exhibits a strong Soret band at ~427 nm and three weaker Q bands at 585, 620, and 655 nm. In contrast, TBA[H2Cor] exhibits a red-shifted Soret band at 455 nm, along with Q bands at 554, 600, and 653 nm. Upon excitation at 430 nm, the neutral free base exhibits strong emission with a maximum at 676 nm, a quantum yield of 6.5% (referenced to coumarin ), and a fluorescence lifetime of 3.79 ns. The H2Cor -anion is also emissive, with a maximum at 675 nm, but with a much lower quantum yield of 3.3% and a somewhat lower fluorescence lifetime of 3.03 ns. a Emission quantum yields were calculated using coumarin (Fem= 0.54) as the reference in degassed CH2Cl2. Emission lifetimes were measured in degassed CH2Cl2 solution.