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Single-walled carbon nanotubes (SWNTs) prepared by pulsed laser vaporization, dispersed, and surfactant-stabilized in near-infrared transparent D2O show weak photoluminescence (PL) from ~1300 up to >1750 nm corresponding to the lowest electronic interband transitions of semiconducting tubes. The characteristic features of this PL, such as a multiple peak emission and a strong excitation wavelength dependence (investigated for λexc from 457 up to 1064 nm), are similar to those reported recently for SWNTs with smaller diameters of around 1 nm (O'Connell et al. Science 2002, 297, 593). The luminescence is significantly polarized with an anisotropy value r of up to 0.32, depending on the excitation and emission wavelengths. The PL data can be used for the structural assignment of emitting tubes; however, in agreement with the results of O'Connell et al., these data are only qualitatively consistent with the tight-binding model widely applied for SWNTs. The luminescence is sensitive to chemical treatment/interactions of SWNTs; much weaker and broader PL was observed above 1300 nm for dispersions of acid-treated tubes in D2O, whereas raw SWNTs in N,N-dimethylformamide show practically no PL. The Raman spectra of dispersed SWNTs differ from those of the solid samples.

Electron autodetachment from isolated metal phthalocyanine−tetrasulfonate tetraanions (MPc(SO3)4^4-) (M=Ni, Cu) was studied at room temperature in an FT-ICR mass spectrometer under UHV conditions. For M = Cu, the electron loss rate was measured for the as-prepared isomer mixture. In the case of M = Ni, two chromatographically purified fractions containing different compositions of constitutional isomers were studied. The observed rate constants for these fractions differed by a factor of 37 ± 5. Photoelectron spectroscopy indicates that both Cu and Ni compounds comprise isomer ensembles which are electronically metastable. Model calculations suggest that the differing electron loss rates observed for the Ni isomer fractions reflect tunneling through repulsive Coulomb barrier surfaces, which are themselves strongly isomer dependent in shape and height.

The photoluminescence (PL) properties of several recently synthesized ligand-stabilized polynuclear gold(I) selenide complexes were investigated. [Au18Se8(dppe)6]Br2 {dppe = bis(diphenylphosphanyl) ethane} (I) is distinguished by the bright-red long-lived PL (phosphorescence) in the solid state, photosensitization of singlet oxygen, ¹O2, in solution, and high photostability. The quantum yield of PL, ϕPL, is (7.5 ± 0.5) × 10^-2 for the polycrystalline I at 293 K (determined using an integrating sphere) and increases up to ~0.8 at 77 K. The quantum yield of ¹O2 is 0.17 ± 0.02 in O2-saturated dichloromethane solutions. [Au10Se4(dpppe)4]Br2 {dpppe = bis(diphenylphosphanyl)pentane} (II) shows a broad near-infrared PL at 880 nm in dichloromethane [ϕPL = (4 ± 1) × 10^-3], which is shifted up to ~1020 nm in the solid II at 77 K (ϕPL ~ 3 × 10^-3). Although the quantum efficiency of II as a luminophor is quite moderate, it is comparable to that of organic infrared laser dyes such as Styryl-20 and IR26. A particular configuration of the Au10Se4 core appears to be crucial for the near-infrared PL:  the “isomeric” complexes [Au10Se4(dppm)4]Br2 {dppm = bis(diphenylphosphanyl) methane} (III) and [Au10Se4(depe)4]Cl2 {depe = bis(diethylphosphanyl) ethane} (IV) show no significant PL.

A [2+2] cycloaddition cap-to-cap C70 dimer with C2h molecular symmetry was synthesized in high yield by pressure treatment of polycrystalline C70 at 1 GPa and 200 °C. It was separated from unreacted monomers by chromatography and characterized by ¹³C NMR, Raman, and infrared spectroscopy, and other methods. Remarkably, only one isomer was produced out of the five possible [2+2] cycloaddition products which have equally low formation energies according to semiempirical modeling calculations. The dimer obtained is the one favored when C70 molecules adopt an ordered packing with parallel D5 axes. The intercage bonding in C140, its thermal stability, and intercage vibrational modes are similar to those found for the C60 dimer, C120. Both dimers photodissociate to the monomers in solution, probably via excited triplet states. The UV absorption and fluorescence properties of C140 are not very different from those of C70, suggesting only weak electronic interactions between the two cages of C140. In comparison, the pressure-induced dimerization of C60, under the conditions used for C70, results mainly in C60 oligomers and polymeric chains, but the dimer C120 could be isolated at low yield when short reaction times (≤5 min) were used.