Photochemical Behavior of Single‐Walled Carbon Nanotubes in the Presence of Propylamine

This report describes the photochemical behavior of single‐walled carbon nanotubes (SWNTs) in the presence of propylamine. The SWNTs are characterized by absorption and Raman spectroscopy. The spectral changes due to photoirradiation indicate that reactions occur predominantly with the metallic SWNTs and small‐diameter SWNTs. The detection of amine radicalcation species by ESR spectroscopy reveals photoinduced electron transfer from the amine to the excited SWNTs. After exposure of the photoirradiated SWNTs to air, the characteristic spectra were recovered, except for that of the small‐diameter SWNTs. The results suggest that, after photoreduction of the SWNTs, subsequent selective sidewall functionalization of the small‐diameter SWNTs occurs.     

Efficient Light-Harvesting Antennae Resulting from the Dense Organization of Dyes into DNA Junctions through d-Threoninol

Herein we report the construction of efficient light-harvesting antennae by hybridization of DNA oligonucleotides containing high densities of fluorophores into DNA junctions through d -threoninol. Six pyrene donors could be incorporated into each arm without self-quenching. A perylene acceptor was located at the center of the junction. Antenna effects of a duplex and three- to eight-way junctions were systematically compared. Six- and eight-way junctions had the highest antenna effects, and their effective absorption coefficients were 8.5 times higher than that of perylene. Interestingly, even-numbered junctions had higher efficiencies than odd-numbered junctions. Nondenaturing gel analyses and fluorescence lifetime measurements demonstrated that the strong odd–even effects were derived from differences in the stability of junctions. The results presented will guide the design of efficient artificial photosynthetic systems.     

Computed Relative Populations of D2(22)‐C84 Endohedrals with Encapsulated Monomeric and Dimeric Water

Water monomer and dimer encapsulations into D₂(22)‐C₈₄ fullerene are evaluated. The encapsulation energy is computed at the M06‐2X/6‐31++G** level, and it is found that the monomer and dimer storage in C₈₄ yields an energy gain of 10.7 and 17.4 kcal mol^?1, respectively. Encapsulation equilibrium constants are computed by using partition functions based on the M06‐2X/6‐31G** and M06‐2X/6‐31++G** molecular data. Under high‐temperature/high‐pressure conditions, similar to that for the encapsulation of rare gases in fullerenes, the computed (H₂O)₂@C₈₄‐to‐H₂O@C₈₄ ratio is close to 1:2.     

Encapsulations of La@C82 and La2@C80 inside single-walled boron nitride nanotubes

Possibility of encapsulations of metallofullerenes inside single-walled boron nitride nanotubes (BNNTs) is studied by using first-principles calculations. We find that both La@C₈₂ and La₂@C₈₀ can be exothermically encapsulated inside the (17, 0) and (14, 7) BNNTs. The minimum diameters of exothermically encapsulating both La@C₈₂ and La₂@C₈₀ inside BNNTs are predicated to be about 13.4 Å.     

Diisobutylaluminum hydride-promoted cyclization of silylated 1,3-dien-5-ynes: Application to total synthesis of a 20-norabietane derivative

The diisobutylaluminum hydride (DIBAL-H)-promoted benzocyclization, recently developed by this group, was adopted for the synthesis of a natural product containing a 9,10-dihydrophenanthrene skeleton to demonstrate its synthetic utility. One of the extracts from the roots of Salvia hydrangea DC. ex Bentham (Lamiaceae), a 20-norabietane derivative, was selected as the target molecule. The key step forming the 9,10-dihydrophenanthrene skeleton was achieved by the DIBAL-H-promoted cyclization of a silylated 1,3-dien-5-yne easily accessible from a substituted α-tetralone.     

The first halogen-substituted cyclotrigermenes: a unique halogen walk over the three-membered ring skeleton and facial stereoselectivity in the Diels-Alder reaction

Dark red crystals of the halogen-substituted cyclotrigermenes [(tBu3Si)3Ge3X; X = Cl, Br, I] were obtained in good yields by the reaction of [(tBu3Si)3Ge3]+.TTFPB- (TTFPB- = tetrakis(2,3,5,6-tetrafluorophenyl)borate) with potassium halides (KCl, KBr, or KI) in diethyl ether. The crystal structures of the halogen-substituted cyclotrigermenes reveal a cis-bent Ge=Ge double bond, caused by the introduction of the electronegative halogen atom on the sp3 germanium atom of cyclotrigermene. In solution, an intramolecular halogen migration over the three-membered ring skeleton was observed. Facial stereoselectivity in the Diels-Alder reaction of new cyclotrigermenes with 2,3-dimethyl-1,3-butadiene is also reported.     

ESR study on the reactivity of two isomers of LaC82 with disilirane

We observed photochemical and thermal addition of disilirane to the LaC₈₂-A isomer, which give new ESR active species. Both ESR spectra of the adducts in photo- and thermal reactions are well simulated by at least six octet components, and the isotropic La coupling constants and g-factors of the six octet components are determined. On the other hand, the reaction of the LaC₈₂-B isomer with disilirane gives no ESR active species. This fact is also verified by mass spectroscopic measurements. The different reactivities with disilirane of the two isomers are not interpreted by a popular view that the two isomers have a different C₈₂ cage structure, but we rather suggest that the origin of the isomers of metallofullerenes should be re-examined.