Combined Raman scattering and ab initio investigation of the interaction between pyrene and carbon SWNT

Raman spectra of HiPco SWNT and SWNT-pyrene films were measured in the 160–1800 cm⁻¹ range. Due to the non-covalent interaction between SWNT and pyrene the most intensive component of the SWNT G mode (1590 cm⁻¹) is downshifted by 2 cm⁻¹ and becomes narrower. Also the intensity of the low-frequency component of the G mode (1550 cm⁻¹) decreases by about 30%. Structures and interaction energies in the complexes of pyrene and zigzag (n, 0) SWNTs [6 ≤ n ≤ 20] were determined at the MP2 level of theory. The BSSE-free geometry optimization of the pyrene-zigzag (12,0) SWNT complex converged to a structure with a 1/2staggered conformation and with an intermolecular distance of 3.5 Å. The BSSE-free interaction energy in the complex is −30.8 kj mol⁻¹. Increasing of the nanotube diameter leads to a higher interaction energy. This energy becomes equal to −37.2 kJ mol⁻¹ in the case of a planar carbon surface.