Revisiting the Laser Dye Styryl-13 As a Reference Near-Infrared Fluorophore: Implications for the Photoluminescence Quantum Yields of Semiconducting Single-Walled Carbon Nanotubes

The near-infrared (NIR) polymethine dye Styryl-13 emitting at ∼925 nm has recently been suggested as a reference fluorophore for determining the quantum yield (QY) of the NIR photoluminescence of dispersed single-walled carbon nanotubes (SWNTs). Ju et al. reported the QY for SWNTs to be as high as 20% on the basis of 11% QY for Styryl-13 in methanol (Science 2009, 323, 1319). We directly compared the fluorescence of Styryl-13 and Styryl-20 (emitting at ∼945 nm) with that of the standard fluorophore Rhodamine 6G using a spectrometer with a broad visible-NIR detection range. QYs of 2.0 (4.5) and 0.52 (0.80)% were determined for Styryl-13 and Styryl-20 in methanol (propylene carbonate), respectively. Correspondingly, the above-mentioned photoluminescence efficiency of SWNTs appears to be strongly overestimated. We also discuss singlet oxygen as an alternative NIR reference. A total QY of 1.4% was measured for the emission of singlet oxygen at 1275 nm, as photosensitized by C70 fullerene in air-saturated carbon tetrachloride

Bistrimethylsilylamide Transition-Metal Complexes as Starting Reagents in the Synthesis of Ternary Cd−Mn−Se Cluster Complexes

The use of bis-trimethylsilylamide transition-metal complexes soluble in organic solvents offers new perspectives for the synthesis of metal chalcogenide cluster molecules, especially for multicomponent clusters. This is illustrated by the synthesis of the mixed cadmium−manganese chalcogenide clusters [Cd4Mn6Se4(SePh)12(PnPr3)4] and [Cd4Mn4S(SePh)14(PnPr3)2] as reported here. These cluster molecules display interesting properties, such as a photoluminescence in the red to near-infrared spectral region, which is particularly bright at temperatures below ∼100 K, and an antiferromagnetic coupling between the manganese(II) ions. Electrospray Fourier transform ion cyclotron resonance mass spectra from the chemically charged clusters in solution show several ionic cluster species which indicate a fast Cd/Mn exchange in solution. Furthermore, single crystal X-ray analysis and magnetic measurements supported by density functional theory calculations suggest a cocrystallization of structural isomers of the ideal cluster composition [Cd4Mn4S(SePh)14(PnPr3)2] as well as of species with the general formula [Cd4+xMn4−xS(SePh)14(PnPr3)2] (x x > 0 Cd enrichment) without a significant decrease in the stability. Thermal cleavage of [Cd4Mn6Se4(SePh)12(PnPr3)4] results, in agreement with the CdSe/MnSe phase diagram, in the formation of a mixture of a hexagonal phase Cd1−xMnxSe (x ≈ 0.5) and a cubic phase Mn1−xCdxSe (x < 0.05)

Bistrimethylsilylamide Transition-Metal Complexes as Starting Reagents in the Synthesis of Ternary Cd−Mn−Se Cluster Complexes

The use of bis-trimethylsilylamide transition-metal complexes soluble in organic solvents offers new perspectives for the synthesis of metal chalcogenide cluster molecules, especially for multicomponent clusters. This is illustrated by the synthesis of the mixed cadmium−manganese chalcogenide clusters [Cd4Mn6Se4(SePh)12(PnPr3)4] and [Cd4Mn4S(SePh)14(PnPr3)2] as reported here. These cluster molecules display interesting properties, such as a photoluminescence in the red to near-infrared spectral region, which is particularly bright at temperatures below ∼100 K, and an antiferromagnetic coupling between the manganese(II) ions. Electrospray Fourier transform ion cyclotron resonance mass spectra from the chemically charged clusters in solution show several ionic cluster species which indicate a fast Cd/Mn exchange in solution. Furthermore, single crystal X-ray analysis and magnetic measurements supported by density functional theory calculations suggest a cocrystallization of structural isomers of the ideal cluster composition [Cd4Mn4S(SePh)14(PnPr3)2] as well as of species with the general formula [Cd4+xMn4−xS(SePh)14(PnPr3)2] (x x > 0 Cd enrichment) without a significant decrease in the stability. Thermal cleavage of [Cd4Mn6Se4(SePh)12(PnPr3)4] results, in agreement with the CdSe/MnSe phase diagram, in the formation of a mixture of a hexagonal phase Cd1−xMnxSe (x ≈ 0.5) and a cubic phase Mn1−xCdxSe (x < 0.05)

Bistrimethylsilylamide Transition-Metal Complexes as Starting Reagents in the Synthesis of Ternary Cd−Mn−Se Cluster Complexes

The use of bis-trimethylsilylamide transition-metal complexes soluble in organic solvents offers new perspectives for the synthesis of metal chalcogenide cluster molecules, especially for multicomponent clusters. This is illustrated by the synthesis of the mixed cadmium−manganese chalcogenide clusters [Cd4Mn6Se4(SePh)12(PnPr3)4] and [Cd4Mn4S(SePh)14(PnPr3)2] as reported here. These cluster molecules display interesting properties, such as a photoluminescence in the red to near-infrared spectral region, which is particularly bright at temperatures below ∼100 K, and an antiferromagnetic coupling between the manganese(II) ions. Electrospray Fourier transform ion cyclotron resonance mass spectra from the chemically charged clusters in solution show several ionic cluster species which indicate a fast Cd/Mn exchange in solution. Furthermore, single crystal X-ray analysis and magnetic measurements supported by density functional theory calculations suggest a cocrystallization of structural isomers of the ideal cluster composition [Cd4Mn4S(SePh)14(PnPr3)2] as well as of species with the general formula [Cd4+xMn4−xS(SePh)14(PnPr3)2] (x x > 0 Cd enrichment) without a significant decrease in the stability. Thermal cleavage of [Cd4Mn6Se4(SePh)12(PnPr3)4] results, in agreement with the CdSe/MnSe phase diagram, in the formation of a mixture of a hexagonal phase Cd1−xMnxSe (x ≈ 0.5) and a cubic phase Mn1−xCdxSe (x < 0.05)

Efficient Quenching of Singlet Oxygen via Energy Transfer to Semiconducting Single-Walled Carbon Nanotubes

Singlet oxygen, 1O2(a1Δg), is efficiently deactivated by single-walled carbon nanotubes (SWNTs) having diameters in the range d ≈ 1−1.6 nm. This is evidenced by quenching of the near-infrared emission of photosensitized 1O2 in water−surfactant dispersions of SWNTs. The observed quenching rate is close to the diffusion-limited value. The smaller diameter SWNTs are found to be comparatively less active, despite the presence of metallic tube types. We therefore attribute the quenching to energy transfer from 1O2 to primarily semiconducting SWNTs having a sufficiently small band gap (d ≥ 1 nm). Remarkably, photogeneration and quenching of up to ∼109 singlet oxygen molecules per nanotube (ultimately limited by degradation of the rose bengal sensitizer) does not affect the photoluminescence and absorption spectra of SWNTs. This indicates that dispersed SWNTs are highly chemically inert toward 1O2 and provides additional support for the proposed physical (energy transfer) quenching mechanism

Near Monochiral Single-Walled Carbon Nanotube Dispersions in Organic Solvents

We describe simple procedures to obtain near monochiral samples of several single-walled carbon nanotube (SWNT) species starting from SWNT raw material. (7,5), (7,6), (10,5), and (9,7) nanotubes were obtained with respective enrichments of up to ∼90% (as estimated from photoluminescence and absorption spectra) by their selective dispersion in toluene with various fluorene-based polymers and subsequent centrifugation. Further highly enriched samples, for instance of (6,5) nanotubes, were prepared by implementing density gradient centrifugation of dispersions of SWNTs in organic solvents with 2,4,6-tribromotoluene as the density gradient additive

Near-Infrared Photoluminescence of Single-Walled Carbon Nanotubes Prepared by the Laser Vaporization Method

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

4-Thiolatobenzoate-Bridged Gold/Zirconium Complex and Its Mononuclear Precursors

The selective synthesis of a AuI complex of 4-mercaptobenzoic acid, namely, [Au(SC6H4-4-COOH)(PMe2Ph)] (1), is reported. It shows interesting photoluminescence (PL) properties, for example, high PL quantum yield, multicomponent emission, and an unusually large PL lifetime. This complex was further applied as a metalloligand for the synthesis of [Cp*2Zr{κ1O-OOCC6H4-4-SAu(PMe2Ph)}{κ2O,O′-OOCC6H4-4-SAu(PMe2Ph)}] (3), one of the rare AuI/ZrIV complexes. For the first time the exchange between the two ligands, which are bound in mono- and bidentate fashion, respectively, could be observed with the help of variable-temperature NMR spectroscopy. For the corresponding monometallic zirconocene complex [Cp*2Zr(κ1O-O2CC6H4-4-SH)(κ2O,O′-O2CC6H4-4-SH)] (2) the activation parameters of this exchange could be determined by line shape analysis

Luminescence in Phosphine-Stabilized Copper Chalcogenide Cluster MoleculesA Comparative Study

The electronic properties of a series of eight copper chalcogenide clusters including [Cu₁₂S₆(dpppt)₄] (dpppt = Ph₂P­(CH₂)₅PPh₂), [Cu₁₂Se₆(dppo)₄] (dppo = Ph₂P­(CH₂)₈PPh₂), [Cu₁₂S₆(dppf)₄] (dppf = Ph₂PCpFeCpPPh₂), [Cu₁₂S₆(PPh₂Et)₈], [Cu₁₂S₆(PEt₃)₈], [Cu₂₄S₁₂(PEt₂Ph)₁₂], [Cu₂₀S₁₀(PPh₃)₈], and [Cu₂₀S₁₀(P^<i>t</i>Bu₃)₈] were investigated by absorption and photoluminescence (PL) spectroscopy as well as time-dependent density functional theory calculations. Major features of the experimental electronic absorption spectra are generally well-reproduced by the spectra simulated from the calculated singlet transitions. Visualization of the nonrelaxed difference densities indicates that for all compounds transitions at higher energies (above ∼2.5 eV, i.e., below ∼495 nm) predominantly involve excitations of electrons from orbitals of the cluster core to ligand orbitals. Conversely, the natures of the lower-energy transitions are found to be highly sensitive to the specifics of the ligand surface. Bright red PL (centered at ∼650–700 nm) in the solid state at ambient temperature is found for complexes with all ‘Cu₁₂S₆’ (E = S, Se) cores as well as the dimeric ‘Cu₂₄S₁₂’, although in [Cu₁₂S₆(dppf)₄], the PL appears to be efficiently quenched by the ferrocenyl groups. Of the two isomeric ‘Cu₂₀S₁₀’ complexes the prolate cluster [Cu₂₀S₁₀(PPh₃)₈] shows a broad emission that is centered at ∼820 nm, whereas the oblate cluster [Cu₂₀S₁₀(P^<i>t</i>Bu₃)₈] displays a relatively weak orange emission at ∼575 nm. The emission of all complexes decays on the time scale of a few microseconds at ambient temperature. A very high photostability is quantitatively estimated for the representative complex [Cu₁₂S₆(dpppt)₄] under anaerobic conditions

Luminescence in Phosphine-Stabilized Copper Chalcogenide Cluster MoleculesA Comparative Study

The electronic properties of a series of eight copper chalcogenide clusters including [Cu₁₂S₆(dpppt)₄] (dpppt = Ph₂P­(CH₂)₅PPh₂), [Cu₁₂Se₆(dppo)₄] (dppo = Ph₂P­(CH₂)₈PPh₂), [Cu₁₂S₆(dppf)₄] (dppf = Ph₂PCpFeCpPPh₂), [Cu₁₂S₆(PPh₂Et)₈], [Cu₁₂S₆(PEt₃)₈], [Cu₂₄S₁₂(PEt₂Ph)₁₂], [Cu₂₀S₁₀(PPh₃)₈], and [Cu₂₀S₁₀(P^<i>t</i>Bu₃)₈] were investigated by absorption and photoluminescence (PL) spectroscopy as well as time-dependent density functional theory calculations. Major features of the experimental electronic absorption spectra are generally well-reproduced by the spectra simulated from the calculated singlet transitions. Visualization of the nonrelaxed difference densities indicates that for all compounds transitions at higher energies (above ∼2.5 eV, i.e., below ∼495 nm) predominantly involve excitations of electrons from orbitals of the cluster core to ligand orbitals. Conversely, the natures of the lower-energy transitions are found to be highly sensitive to the specifics of the ligand surface. Bright red PL (centered at ∼650–700 nm) in the solid state at ambient temperature is found for complexes with all ‘Cu₁₂S₆’ (E = S, Se) cores as well as the dimeric ‘Cu₂₄S₁₂’, although in [Cu₁₂S₆(dppf)₄], the PL appears to be efficiently quenched by the ferrocenyl groups. Of the two isomeric ‘Cu₂₀S₁₀’ complexes the prolate cluster [Cu₂₀S₁₀(PPh₃)₈] shows a broad emission that is centered at ∼820 nm, whereas the oblate cluster [Cu₂₀S₁₀(P^<i>t</i>Bu₃)₈] displays a relatively weak orange emission at ∼575 nm. The emission of all complexes decays on the time scale of a few microseconds at ambient temperature. A very high photostability is quantitatively estimated for the representative complex [Cu₁₂S₆(dpppt)₄] under anaerobic conditions