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

Abstract

A series of isoindazole-C(60) 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 C(60). 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 C(60) moiety. Electrochemical properties of the new dyads 4a-c show a similar electron affinity with respect to C(60). 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 charge-separation rates and efficiencies via the excited singlet states of the fullerene moiety were evaluated. The yields of the triplet states in polar solvent decrease with the electron-donating ability, supporting the competitive formation of the charge-separated state with the intersystem crossing from the excited states. Thus, isoindazole[60]fullerene 4b can be considered a molecular switch with an AND logic gate.

Pyrazolino[60]fullerene–Oligophenylenevinylene Dumbbell‐Shaped Arrays: Synthesis, Electrochemistry, Photophysics, and Self‐Assembly on Surfaces

“…Four of them (E [60]fullerene derivatives, the first reduction potentials (E 1 red ) are analogous to that of pristine C 60 and shifted to more positive values relative to other fullerene derivatives due to the ÀI effect of the pyrazoline ring. [53,54] On the oxidation side, an irreversible one-electron wave was observed at around + 0.44 V (F-3 PV-F) and + 0.35 V (F-5 PV-F), while these waves appear at + 0.34 V and + 0.31 V in F-3 PV and F-5 PV, respectively. Similarly, bishydrazones 6 and 12 show the same oxidation around + 0.37 V. These values can be assigned to the oxidation of the OPV moiety, in agreement with previous reports.…”

“…[ 19] The second oxidation wave in the two bis-hydrazones must be attributed to the hydrazone moiety; [53] an additional wave is observed in F-3 PV and F-5 PV at around + 0.6 V, assigned to the oxidation of the aldehyde group.…”

“…Compounds F 1 and F 2 were prepared as previously reported. [19,53] The OPV derivatives 3 PV and 5 PV were obtained by LiAlH 4 reduction of the corresponding bis-aldehydes 5 and 11, respectively.…”

Mass Spectrometry Studies of the Retro-Cycloaddition Reaction of Pyrrolidino and 2-Pyrazolinofullerene Derivatives Under Negative ESI Conditions

“…3-Alkyl-2-substituted pyrazolinofullerenes (1-3) (Chart 1) were prepared according to the previously reported synthetic methods [34,35]. Purity and identity were assessed and confirmed by spectroscopic methods.…”

Microwave‐Assisted Cycloaddition Reactions

“…Oxidation of the aldehydes 68 with I 2 in aqueous ammonia gave the intermediate nitriles, which underwent 1,3-dipolar cycloadditions with sodium azide to afford 5-aryltetrazoles (69) in 70-83% overall yields. In a similar way, benzyl alcohol (70a), N-Cbz-prolinol (70b), and a tyrosine-derived primary alcohol (70c) were converted into 1,2,3,4-tetrazoles (71) (76) and azides in ILs derived from alkylimidazoles (Scheme 17.9) [33]. The temperature was first optimized to achieve complete conversion.…”