RESUMO
Endohedral metallofullerenes are capable of holding peculiar metal clusters inside the carbon cage. Additionally, these display many chemical and physical properties originating from the complexation between the metal clusters and carbon cages, which could be acquired for wide applications. In this study, two metallofullerenes (Ce2O@C88 and Ce3N@C88) with an identical large C88-D2(35) cage, and their molecular structures and single-molecule conductance properties were investigated comparatively. Characterizations of UV-vis-NIR absorption spectroscopy, Raman spectroscopy, and DFT calculations were employed to determine the geometries and electronic structures of Ce2O@C88 and Ce3N@C88. These molecules revealed varied energy gaps, structural parameters, vibrational modes, and molecular frontier orbitals. Although the two metallofullerenes have an identical cage isomer of C88-D2(35), their different endohedral clusters can influence their structures and physicochemical properties. Furthermore, the single-molecule conductance properties were measured using the scanning tunneling microscopy break junction technique (STM-BJ). The experimental results revealed that Ce2O@C88 has a higher conductance than Ce3N@C88 and C60. This revealed the cluster-dependent electron transportation as well as the significant research value of metallofullerenes with large carbon cages. These results provide guidance for fabricating single-molecule electronic devices.
RESUMO
Quantum interference (QI) has been identified as a promising strategy for designing molecular-scale electronic devices. Heteroatom doping can effectively tailor the local structures and electronic states of intrinsic molecules, and endow them with modified electron transport properties. Herein, the impacts of multiple heteroatom substitution on destructive quantum interference (DQI) have been investigated based on tripodal meta-linked phenyl derivatives. Orbital views based on the Hückel method qualitatively predict the meta-anchored molecules with DQI features, while the introduction of nitrogen atoms can alleviate the suppression of DQI at the Fermi level (EF). This is generally consistent with the movement or even removal of the antiresonance dips in transmission spectra. The substituent on position 2 can raise the antiresonance energy, while the substituent on position 4 or 6 can lower the antiresonance energy. When more than one nitrogen atom is incorporated, the impact of the substitution on positions 4 and 6 can be superimposed and the substitution on positions 2 and 4 can be partly cancelled. The experimental single-molecule conductance for tripodal molecules follows the trend of 0N-3SMe < 1N-3SMe < 3N-3SMe < 2N-3SMe, in agreement with the theoretical prediction. Additionally, the regulation is the intrinsic property depending on the position and number of the nitrogen atoms in the backbone and is irrelevant to the number and type of the anchoring groups. Our findings provide qualitative guidance for tuning the electron transport based on DQI in heterocycle molecular devices.
RESUMO
Tubular fullerenes can be considered as end-capped carbon nanotubes with accurate structure, which are promising nanocarbon materials for advanced single-molecule electronic devices. Herein, we report the synthesis and characterization of a metallofullertube Ce2 @D5 (450)-C100 , which has a tubular C100 cage with a carbon nanotube segment and two fullerene end-caps. As there are structure correlations between tubular Ce2 @D5 (450)-C100 and spherical Ce2 @Ih -C80 , their structure-property relationship has been compared by means of experimental and theoretical methods. Notably, single-molecule conductance measurement determined that the conductivity of Ce2 @D5 (450)-C100 was up to eight times larger than that of Ce2 @Ih -C80 . Furthermore, supramolecular assembly of Ce2 @D5 (450)-C100 and a [12]CPP nanohoop was investigated, and theoretical calculations revealed that metallofullertube Ce2 @D5 (450)-C100 adopted a "standing" configuration in the cavity of [12]CPP. These results demonstrate the special nature of this kind of metallofullertube.
