Single-walled carbon nanotube (SWCNT) hybrids with meso-5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4) and 10,15, have been studied by the resonance Raman spectroscopy and by ab initio and molecular dynamic calculations. A comparison of the intensities of the bands assigned in the Raman spectrum to the radial breathing mode, as well as the relative band positions corresponding to the tangential modes of the hybrids with respect to the positions of these modes in the spectrum of the pristine SWCNT, indicates that the interaction of the nanotube with TMPyP4 is stronger than with TPP. A structure calculation (by the DFT/M05-2X method) of the TMPyP4 molecule adsorbed to a fragment of the zigzag (10,0) SWCNT surface shows that porphyrin adapts a saddled structure with the binding energy to the nanotube of -72.0 kcal/mol. The interaction energy in the complex of a TPP molecule with SWCNT, whose molecular structure is similar to TMPyP4, is only -19.3 kcal/mol and TPP does not adapt the saddled structure on the nanotube surface. The calculated interaction energies of the nanotube surface with the porphin core (-14.3 kcal/mol), the charged fragment of TMPyP4 (methylpyridinium) (-25.8 kcal/ mol) and a neutral benzene molecule (-4.6 kcal/mol), which mimic the side residues of TMPyP4 and TPP, respectively, suggest that the stronger interaction between SWCNT and the TMPyP4 molecule is due to the cation-π interaction. The SWCNT:TMPyP4 complex formation in the aqueous solution has been modeled by the molecular dynamics method. The modeling showed that the hybrid is also stable in the water solution.
Noncovalent functionalization of graphene with organic molecules offers a direct route to multifunctional modification of this nanomaterial, leading to its various possible practical applications. In this work, the structures of hybrids formed by linear heterocyclic compounds such as imidazophenazine (F1) and its derivatives (F2-F4) with graphene and the corresponding interaction energies are studied by using the DFT method. Special attention is paid to the hybrids where the attached molecule is located along the graphene zigzag (GZZ ) and armchair (GAC ) directions. The interaction energies corresponding to the graphene hybrids of the F1-F4 compounds for the two directions are found to be distinct, while tetracene (being a symmetrical molecule) shows a small difference between these binding energies. It is found that the back-side CH3 and CF3 groups have an important influence on the arrangements of F1 derivatives on graphene and on their binding energies. The contribution of the CF3 group to the total binding energy of the F3 molecule with graphene is the largest (3.4 kcal mol(-1) ) (the GZZ direction) while the CH3 group increases this energy of F2 only by 2.0 kcal mol(-1) (the GAC direction). It is shown that replacing the carbons with other atoms or adding a back-side group enables one to vary the polarizability of graphene.
IR Spectroscopy is used for the first time to study the absorption spectra (400–1700cm−1 range) of imidazo-[4,5-d]-phenazine (F1) and its derivatives 2-methylamidazo-[4,5-d]-phenazine (F2), 2-fluorodimethylimidazo-[4,5-d]-phenazine (F3), and 1,2,3-triazolo-[4,5-d]-phenazine (F4) in a low-temperature argon matrix (10K). The spectra of these compounds are analyzed using computed frequencies and intensities of harmonic vibrations obtained by the quantum-mechanical DFT method (B3LYP∕6-31++G** and M05-2X∕6-31++G**). The low-temperature IR spectra of the compounds F1–F4 are in good agreement with the computed spectra. The spectra obtained contain bands which are common to all compounds F1–F4 as well as bands which are characteristic to each individual compound. The strongest transformations in the IR spectra of the F2–F4 compounds relative to the F1 spectrum are observed for the compound F4 where they are due to the substitution of a nitrogen atom for a carbon atom in the imidazole ring. A comparative analysis of the spectra of the isolated molecules with the spectra of polycrystalline samples in KBr pellets is performed. The structures, interaction energies, and the harmonic frequencies and their intensities are calculated for hydrogen-bonded and stack dimers of these compounds. The computed dimer spectra describe well the IR spectra of the compounds F1–F4 in KBr pellets.
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