Excitonic Interactions in Covalently Linked Porphyrin Dimers with Rotational Freedom

Abstract

Experimental and calculated absorption spectra are compared for four different porphyrin dimers covalently linked by alkyl- or phenyl bridges. The spectra of the corresponding monomers were used as a reference to determine the experimental exciton,ic shift(s) of the absorption spectrum in the Soret region. The excitonic interaction was calculated using the point dipole approximation and taking into account the restricted conformational freedom of the monomeric units in the dimers due to steric constraints. The constraints were independently verified by magnetic dipole-dipole broadening of the EPR spectra of several ( CuTPP ) 2 - substituted dimers. The observed and calculated absorption spectra agree at least semiquantitatively.