Pulsed ENDOR spectroscopy of the interior protons of free-base porphin in its lowest photoexcited triplet state, in ann-octane single crystal

Through the use of the pulsed ENDOR technique, we have obtained the magnetic resonance spectra of the interior protons of free-base porphin in its lowest photoexcited triplet state in a single crystal of n-octane. The values of the components, in the fine structure principal axis system, of the proton-electron hyperfine interaction have been ascertained, and clearly illustrate a departure from D 2h molecular symmetry. The measured tensors have been used to obtain the spin densities at the porphin nitrogen atoms, and the locations of the protons within the ring.