The Isoindazole Nucleus as a Donor in Fullerene‐Based Dyads. Evidence for Electron Transfer.

Abstract

A series of isoindazole-C60 dyads 4a−c based on pyrazolino[60]fullerene have been prepared by 1,3-dipolar cycloadditions of the nitrile imines, generated in situ from hydrazones 3a−c, to C60. Molecular orbital calculations for 4b revealed that the electron distribution of the HOMO is located on the isoindazole moiety, while the electron distribution of the LUMO is located on the C60 moiety. Electrochemical properties of the new dyads 4a−c show a similar electron affinity with respect to C60. Charge-transfer interactions in the ground state between the isoindazole ring and the fullerene cage are predicted by the molecular orbital calculations and confirmed by electrochemical studies in 4a,b. Steady-state fluorescence emission spectra of dyads 4a−c show that fluorescence intensities in polar benzonitrile solvent decrease with increasing electron-donating ability of the substituent attached on the isoindazole group. This was confirmed by the shortening of fluorescence lifetimes, from which intramolecular cha...