The rate constants of the quenching processes of the lowest singlet excited state of naphthalene, pyrene, anthracene, 9,10-diphenylanthracene, tetracene, coronene, rubrene, and protoporphyrin IX dimethyl ester, and of the lowest triplet excited state of anthracene, tetracene, and coronene by Eu3+ in acetonitrile solution have been measured. Singlet excited states are quenched with practically diffusion-controlled rates, the main quenching products being radical ions and triplets. Triplet excited states are quenched with very low rate constants (≤106 M-1 s-1) in spite of the strong exoergonicity of the electron-transfer quenching process. Comparison with the results obtained with Rh(bpy)33+ as a quencher and examination of the log kq vs. ΔG (for outer-sphere electron transfer) plot indicate that the reactions between triplets and Eu3+ are strongly nonadiabatic. It is suggested that the observed differences between the rate constants of singlet and triplet quenching may be related to the higher polarizability of singlets which favors a stronger electronic interaction with the highly charged Eu3+ ions. © 1982 American Chemical Society.
Quenching of Singlet and Triplet Excited States of Aromatic Molecules by Europium Ions
INDELLI, Maria Teresa;
1982
Abstract
The rate constants of the quenching processes of the lowest singlet excited state of naphthalene, pyrene, anthracene, 9,10-diphenylanthracene, tetracene, coronene, rubrene, and protoporphyrin IX dimethyl ester, and of the lowest triplet excited state of anthracene, tetracene, and coronene by Eu3+ in acetonitrile solution have been measured. Singlet excited states are quenched with practically diffusion-controlled rates, the main quenching products being radical ions and triplets. Triplet excited states are quenched with very low rate constants (≤106 M-1 s-1) in spite of the strong exoergonicity of the electron-transfer quenching process. Comparison with the results obtained with Rh(bpy)33+ as a quencher and examination of the log kq vs. ΔG (for outer-sphere electron transfer) plot indicate that the reactions between triplets and Eu3+ are strongly nonadiabatic. It is suggested that the observed differences between the rate constants of singlet and triplet quenching may be related to the higher polarizability of singlets which favors a stronger electronic interaction with the highly charged Eu3+ ions. © 1982 American Chemical Society.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
