Chemical reactivity in nucleophilic cycloaddition to C70: vibronic coupling density and vibronic coupling constants as reactivity indices

A theoretical investigation into the role of catalyst support and regioselectivity of molecular adsorption on a metal oxide surface: NO reduction on Cu/γ-alumina

The role of catalyst support and regioselectivity of molecular adsorption on a metal oxide surface is investigated for NO reduction on a Cu/γ-alumina heterogeneous catalyst. For the solid surface, computational models of the γ-alumina surface are constructed based on the Step-by-Step Hydrogen Termination (SSHT) approach. Dangling bonds, which appear upon cutting the crystal structure of a model, are terminated stepwise with H atoms until the model has an appropriate energy gap. The obtained SSHT models reflect the realistic infrared (IR) and ultraviolet-visible (UV/Vis) spectra. Vibronic coupling density (VCD), as a reactivity index, is employed to elucidate the regioselectivity of Cu adsorption on γ-alumina and that of NO adsorption on Cu/γ-alumina in place of the frontier orbital theory that could not provide clear results. We discovered that the highly dispersed Cu atoms are loaded on Lewis-basic O atoms, which is known as the anchoring effect, located in the tetrahedral sites of the γ-alumina surface. The role of the γ-alumina support is to raise the frontier orbital of the Cu catalyst, which in turn gives rise to the electron back-donation from Cu/γ-alumina to NO. In addition, the penetration of the VCD distribution of Cu/γ-alumina into the γ-alumina support indicates that the excessive reaction energy dissipates into the support after NO adsorption and reduction. In other words, the support plays the role of a heat bath. The NO reduction on Cu/γ-alumina proceeds even in an oxidative atmosphere because the Cu-NO bond is strong compared to the Cu-O2 bond.

cis-1 Isomers of tethered bismethano[70]fullerene as electron acceptors in organic photovoltaics

Isomer-controlled [70]fullerene bis-adducts can achieve high performance as electron-acceptors in organic photovoltaics (OPVs) because of their stronger absorption intensities than [60]fullerene derivatives, higher LUMO energy levels than mono-adducts, and less structural and energetic disorder than random isomer mixtures. Especially, attractive are cis-1 isomers that have the closest proximity of addends owing to their plausible more regular close packed structure. In this study, propylene-tethered cis-1 bismethano[70]fullerene with two methyl, ethyl, phenyl, or thienyl groups were rationally designed and prepared for the first time to investigate the OPV performances with an amorphous conjugated polymer donor (PCDTBT). The cis-1 products were found to be a mixture of two regioisomers, α-1-α and α-1-β as major and minor components, respectively. Among them, the cis-1 product with two ethyl groups (Et2-cis-1-[70]PBC) showed the highest OPV performance, encouraging us to isolate its α-1-α isomer (Et2-α-1-α-[70]PBC) by high-performance liquid chromatography. OPV devices based on Et2-cis-1-[70]PBC and Et2-α-1-α-[70]PBC with PCDTBT showed open-circuit voltages of 0.844 V and 0.864 V, respectively, which were higher than that of a device with typical [70]fullerene mono-adduct, [70]PCBM (0.831 V) with a lower LUMO level. However, the short-circuit current densities and resultant power conversion efficiencies of the devices with Et2-cis-1-[70]PBC (9.24 mA cm-2, 4.60%) and Et2-α-1-α-[70]PBC (6.35 mA cm-2, 3.25%) were lower than those of the device with [70]PCBM (10.8 mA cm-2, 5.8%) due to their inferior charge collection efficiencies. The results obtained here reveal that cis-1 [70]fullerene bis-adducts do not guarantee better OPV performance and that further optimization of the substituent structures is necessary.

Unique cohesive nature of the β1-isomer of [70]PCBM fullerene on structures and photovoltaic performances of bulk heterojunction films with PffBT4T-2OD polymers

Decreasing the amount of a diastereomer of β-[70]PCBM with high aggregation tendency improved the performances of OPV devices with PffBT4T-2OD:[70]PCBM films.

Reactivity of endohedral metallofullerene la2@c80 in nucleophilic and electrophilic attacks: vibronic coupling density approach

The regioselectivities of La2@C80 in thermal nucleophilic and electrophilic attacks were theoretically investigated using vibronic coupling density (VCD) analysis. Nucleophilic and electrophilic cycloadditions to La2@C80 were experimentally reported to yield [6,6] and [6,5] adducts, respectively, as major products. VCD analysis provided a clear explanation for these experimental results. For nucleophilic reactions, it was found that the reactive [6,6] bonds did not have a large lowest unoccupied molecular orbital (LUMO) density and Fukui function but a large potential derivative with respect to a reaction mode. The VCD illustrates the origin of the interaction between the electronic and vibrational states. On the other hand, conventional reactivity indices such as frontier orbital density take only the electronic state into account. The result suggested that the stabilization due to vibronic couplings plays an important role in the regioselectivity of nucleophilic cycloadditions. The VCD with respect to the effective mode could provide a picture of the functional groups, which are the double bonds of ethylene moieties. VCD analysis with respect to hypothetical localized modes enabled the quantitative prediction of regioselectivities.