Hindered Internal Conversion in Rigid Media: Thermally Nonequilibrated3IL and3CT Emissions from [Cu(5-X-phen)(PPh3)2]+ and [Cu(4,7-X2-phen)(PPh3)2]+Systems in a Glass at 77 K

Dominick J. Casadonte, David R. McMillin

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Abstract

The photophysical properties of two series of mixed-ligand copper(I) complexes involving substituted 1,10-phenanthroline (phen) derivatives have been investigated in low-temperature glasses. In particular, the absorption and emission spectra of complexes of the type [Cu(5-X-phen)(PPh3)2]+or [Cu(4,7-X2-phen)(PPh3)2]+have been characterized. The emission spectra are noteworthy because separate, nonequilibrated emissions are observed from two triplet excited states with distinct orbital parentages. The vibronically structured component of the emission has a lifetime of the order of 10 ms and has been assigned to a3IL (intraligand) excited state, while the broad, unstructured component, which has a lifetime of the order of 100 ys, has been attributed to a3CT (charge-transfer) excited state. Although microenvironmental heterogeneity exists within the sample, it is argued that separate emissions occur because there is a structurally imposed barrier against interconversion between the3IL and3CT states in a rigid matrix. The relative energies of the3CT and3IL excited states vary, but the maximum energy difference between the zero-zero energies of the two states is about 1000 cm-1. In all cases the emission from the lower energy component is more intense, and the relative intensity of the higher energy component decreases as the separation between states increases. Internal conversion beteen the two triplet states is viewed as an intramolecular electron-transfer process whose rate depends upon the driving force.

Original languageEnglish
Pages (from-to)331-337
Number of pages7
JournalJournal of the American Chemical Society
Volume109
Issue number2
DOIs
StatePublished - Jan 1 1987

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