Investigation of Interporphyrin Charge Resonance of Dihedral Angle Controlled Porphyrin Dimers by Resonance Raman Spectroscopy and MO Approaches

Abstract

Strongly interacting porphyrin dimers as a form of cofacial or side-to-side linkage have been ideally suited for investigation on the structure−electronic property relationship in porphyrin dimers. The relative orientation and interchromophore distance determined by the dihedral angle between the two porphyrin units are key factors in controlling the interchromophoric interaction. In the present work, directly linked porphyrin dimers with a systematic change in the dihedral angle between the two porphyrin planes have been investigated by resonance Raman (RR) and emission spectroscopies. Extremely strong molecular orbital interactions between the porphyrin units by decreasing the dihedral angle give rise to strongly enhanced interporphyrin charge-resonance transitions. With a decrease of the dihedral angle, unique RR spectra of the porphyrin dimers were also observed depending on the excitation wavelengths of 406.7, 457.9, and 488.0 nm. With the aid of supermolecular MO approaches it was found that the cha...