Endohedral Copper(II)acetylacetonate/Single-Walled Carbon Nanotube Hybrids Characterized by Electron Paramagnetic Resonance

Abstract

The encapsulation of an organometallic paramagnetic molecule, copper(II) acetylacetonate (Cu(acac)2), inside single-walled carbon nanotubes (SW CNTs) is studied using continuous wave electron paramagnetic resonance (EPR). By preparing samples from fully opened as well as from closed SW CNTs, the EPR spectra of encapsulated and nonencapsulated molecules can be clearly identified. The EPR spectrum originating from the encapsulated molecules is unchanged by dispersion of the endohedral nanohybrids in a solvent or by solubilization of the nanohybrids in water using bile salt surfactants, demonstrating that the CNTs protect them from changes in their external environment. The EPR parameters obtained for the encapsulated molecules show that they experience an extremely apolar environment. From the dipolar broadening of the EPR lines of the nanohybrids, the distances between the encapsulated molecules inside the CNTs can be estimated by adapting Van Vleck’s method of moments for the case of a one-dimensional array of molecules. Furthermore, a combination of orientation dependent EPR experiments and polarized Raman scattering on preferentially aligned CNT hybrids in stretched polymer film samples yields information on the orientational distribution of the encapsulated molecules inside the SW CNTs.

Diameter-Dependent Optical Absorption and Excitation Energy Transfer from Encapsulated Dye Molecules toward Single-Walled Carbon Nanotubes

“…In general, bathochromic shifts of the dye absorption can originate from a change in dielectric environment or intermolecular electronic coupling in dimers or aggregate structures. 40 The SWCNT internal cavity by itself is known to act as a very apolar environment 41 and thus cannot explain the redshift. Moreover, the redshift (∼220 meV) observed for SQ molecules in the SQ@LV950-ATPE sample is much larger than typically observed for changes in dielectric environment of isolated SQ molecules in solution: the wavelength of maximum absorbance for SQ dissolved in acetonitrile (ε = 37) and toluene (ε = 2.93) differs by less than 10 meV (see Figure S13 ).…”

An ENDOR and DFT analysis of hindered methyl group rotations in frozen solutions of bis(acetylacetonato)-copper(ii)

“…In fact, the dependence of the g/ Cu A values on the [Cu(acac) 2 ] environment were recently used to determine the interaction of the complex with carbon nanotubes, highlighting the sensitivity of the spin Hamiltonian parameters on the surroundings. 14 The Q-band CW EPR spectrum of the 'dry' sample is shown in Fig. 1c, along with the corresponding simulation.…”

“…The bis(acetylacetonato)-copper(II) complex [Cu(acac) 2 ] is one of the most extensively studied d-transition metal compounds by Electron Paramagnetic Resonance (EPR) spectroscopy (Scheme 1). [1][2][3][4][5][6][7][8][9][10][11][12][13][14] This can largely be attributed to its relative simplicity, ease of preparation and favourable stability constant, which collectively facilitate the investigation of this complex in single crystal, [1][2][3][4] frozen solution [5][6][7][8][9][10][11][12] and powder (doped Cu-Pd solid solution) 13 forms. The simple square planar arrangement of [Cu(acac) 2 ] with four oxygen donors forming the inner coordination sphere, has led to its inclusion in the Peisach and Blumberg 'truth tables', correlating trends in g/ Cu A with coordination environment for Cu(II) systems.…”

Effects of copper and vanadium deposition in multi-walled hydrogen trititanate and mixed-phase anatase/trititanate nanotubes

“…6a): (g z1 = 2.34, A z1 = 500 MHz), (g z2 = 2.36, A z2 = 450 MHz), and (g z3 = 2.38, A z3 = 400 MHz). These values lie in between the principal values of [Cu(H 2 O) 6 ] 2+ (g z = 2.422, A z = 402 MHz 32 ) and Cu(acac) 2 in chloroform (g z = 2.286, A z = 524 MHz 33 ). This indicates that we probably have Cu(II) sites with a varying number of ligating acac and water (or titanol groups).…”