Hindered Internal Conversion in Rigid Media. Thermally Nonequilibrated 3IL and 3CT Emissions from + and 2-phen)(PPh3)2>+ Systems in a Glass at 77 K

Article abstract of DOI:10.1021/ja00236a006

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 ⁺ or 2-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 a ³IL (intraligand) excited state, while the broad, unstructured component, which has a lifetime of the order of 100 μs, has been attributed to a ³CT (charge-transfer) excited state.Although microenviromental heterogeneity exists within the sample, it is argued that separate emissions occur because there is a structurally imposed barrier against interconversion between the ³IL and ³CT states in a rigid matrix.The relative energies of the ³CT and ³IL 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 between the two triplet states is viewed as an intramolecular electron-transfer process whose rate depends upon the driving force.