The single site fluorescence and excitation spectra of free base porphin in an n-octane crystal at 5 K are reported. The vibrational frequencies of the ground and excited states (Q x , Q y and B bands) have been determined from the spectra. The Q x region is very similar to the previously reported results from supersonic jet expansion. However, the Q y region is quite different in the jet and mixed crystal; the crystal spectrum exhibits extensive vibronic coupling. The Soret band shows little vibronic structure.