SPECTROSCOPIC CHARACTERIZATION OF TRIPLE-DECKER LANTHANIDE PORPHYRIN SANDWICH COMPLEXES - EFFECTS OF STRONG PI-PI-INTERACTIONS IN EXTENDED ASSEMBLIES

Electrochemical, optical absorption, near-infrared, infrared, resonance Raman, and electron paramagnetic resonance data are reported for several neutral and singly oxidized triple-decker lanthanide porphyrin sandwich complexes Ln2(OEP)3 (Ln = La(III), Ce(III), Eu(III); OEP = octaethylporphyrin). The data indicate that there are strong ππ interactions between the porphyrin macrocycles in all of the complexes. As a consequence, the hole in the porphyrin π system of the Ln2(OEP)3+ systems is delocalized over all three rings on the vibrational and electronic time scales. The singly oxidized complexes exhibit a characteristic electronic absorption band at very low energies (ca. 2200 nm). This absorption arises as a direct consequence of the strong ππ interactions between the rings. A molecular orbital scheme is proposed that accounts for this low-energy feature as well as a number of other properties of the triple-decker sandwich complexes. © 1990, American Chemical Society. All rights reserved.