Mechanism of Intramolecular Energy Transfer in Rare Earth Chelates as Revealed by Infrared Absorption Measurements

Abstract

Abstract The purpose of this paper is to clarify the mechanism of intramolecular energy transfer from the triplet state of the ligand to the excited levels of the central ion in rare earth chelates. As to seven kinds of samarium β-diketonates, the frequency of infrared absorption due to the stretching vibration of the chelate bond, \ ildeνMO, and the manner of energy transfer are investigated. The probability of energy transfer is estimated from the ratio of the intensity of the samarium emission to that of the ligand phosphorescence, ISm⁄IPh. The overlap integral, S, between the ligand phosphorescence spectrum and the samarium absorption spectrum is obtained. It was found that a linear relation roughly holds between log{(ISm⁄IPh)⁄S} and \ ildeνMO. On the basis of this fact, one is led, by making some arguments, to the conclusion that intramolecular energy transfer is dominated by the resonance mechanism due to the exchange interaction of the π electron system of the ligand triplet state with the f electron system of the central rare earth ion.