COPPER(I)-PHENANTHROLINE AND RUTHENIUM(II)-TERPYRIDYL COMPLEXES: FACTORS INFLUENCING THE EXCITED STATE LUMINESCENCE (EXCIPLEX, QUENCHING)

JON RICHARD KIRCHHOFF, Purdue University

Abstract

The photophysical properties of a series of homochelated complexes of the type Cu(NN)(,2)('+) have been measured. For all the complexes studied, the emission intensity decreases as the solution temperature is lowered. This is interpreted in terms of two emitting states where population of the upper level, which has a more favorable radiative rate constant, requires thermal energy. A detailed temperature analysis has been carried out for Cu(dmp)(,2)('+), Cu(tpp)(,2)('+) and Cu(dpp)(,2)('+). The results indicate the lowest energy emitting state exhibits a radiative rate constant of ca. 10('3) s('-1), typical of a triplet state. The other state, a singlet state, lies some 1500-1800 cm('-1) to higher energy and exhibits a rate constant of ca. 10('7) s('-1). Both states are assumed to derive from the lowest energy charge-transfer configuration of the complex. The Lewis base quenching of the luminescence from Cu(dmp)(,2)('+) and Cu(dpp)(,2)('+) has been investigated. Systematic quenching studies reveal that the degree of quenching depends on the sterics of the quencher and the size of the substituents adjacent to the coordinating nitrogens. The quenching mechanism can be understood in terms of an associative reaction between the donating Lewis base and the electron deficient metal center, which occurs during the lifetime of the excited state. The associated complex is viewed as a nonemissive exciplex. The crystal and molecular structures of Cu(dmp)(PPh(,3))(,2) NO(,3) and Cu(phen)(PPh(,3))(,2) NO(,3)(.)2EtOH have been solved. The results indicate that significant interligand steric repulsions, present in the dmp complex, account for the contrasting solution behavior between these complexes. In addition, the steric effects have been linked to the hindrance of the solvent-induced quenching pathway. The photochemical and photophysical properties of Ru(dpt)(,2)('2+) have been described. The visible absorbing complex shows little or no detectable emission at room temperature or in a rigid glass at 77 K; however, upon irradiation the complex undergoes photoanation. The properties of Ru(dpt)(,2)('2+) are compared with other ruthenium(II) bis-terpyridyl complexes. A kinetic scheme is proposed in which non-radiative decay occurs a d-d excited state which is prone to undergo ligand substitution processes.

Degree

Ph.D.

Subject Area

Chemistry

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