Interactions of metal phthalocyanines with Stone-Wales defects on single-walled carbon nanotubes: A theoretical study

A density functional theory (DFT) analysis of the influence of Stone-Wales (SW) defect incorporated into an armchair and zigzag single-walled carbon nanotube (SWCNT) models (ANT and ZNT, respectively) functionalized noncovalently with unsubstituted nickel(II) and cobalt(II) phthalocyanines (MPcs, where M=Ni2+, Co2+) as representative Pcs was performed at the PBE-D/DNP level of theory. The data obtained (bonding and frontier orbital energies, geometries, charge and spin distribution, etc.) were compared with the DFT results for similar systems based on defect-free nanotube models. SW defect was incorporated into each nanotube model in different orientations with respect to SWCNT axis, depending on whether the (7,7) junction is tilted (ANT_SW-T and ZNT_SW-T models), parallel (ANT_SW-P), or perpendicular (ZNT_SW-P) with respect to the SWCNT axis. The formation energy of SW defect-containing SWCNTs depends on the defect orientation and nanotube chirality, decreasing in the order of ANT_SW-P > ZNT_SW-T > ANT_SW_T > ZNT_SW-P; in all cases, HOMO-LUMO gap narrowing was observed. Phthalocyanine molecules in MPc + SWCNT_SW complexes undergo strong bending distortion in order to increase the area of their contact with the nanotube sidewall. As compared to NiPc and CoPc dyads with defect-free nanotubes, formation energy Delta E decreased (that is, bonding strength increased) for three complexes, for four complexes an opposite effect was found, and in one case the variation was negligible. For most dyads, gap narrowing was observed, as compared to both defect-free complexes and SW defect-containing isolated nanotube models.