Photochemistry and Hole-Burning of Free-Base Porphin and Chlorin in n-Alkane Hosts at 4.2 K

Abstract
It is known that the porphyrin free-base (H2P) is incorporated in an n-octane crystal in an oriented fashion in at least two different sites (A, B).1,2 In each of these sites two tautomeric forms occur (1, 2) which have their N[sbnd]H… H[sbnd]N axes at right angles. Due to a difference in interaction with the crystalline host for the two orientations, the optical spectra show a doublet structure for each site.1 The separation between the doublet components depends both on the n-alkane host and on the site occupied.2