Excitonic interactions in covalently linked porphyrin dimers with rotational freedom

Experimental and calculated absorption spectra are compared for four differ ent porphyrin dimers covalently linked by alkyl- or phenyl bridges. The spe ctra of the corresponding monomers were used as a reference to determine th e experimental excitonic shift(s) of the absorption spectrum in the Soret r egion. The excitonic interaction was calculated using the point dipole appr oximation and taking into account the restricted conformational freedom of the monomeric units in the dimers due to steric constraints. The constraint s were independently verified by magnetic dipole-dipole broadening of the E PR spectra of several (CuTPP)(2)-substituted dimers. The observed and calcu lated absorption spectra agree at least semiquantitatively. Copyright (C) 1 999 John Wiley & Sons, Ltd.