Possible SQ stacking
geometries in different diameter SWCNTs. (a)
Calculated structure of a single SQ molecule in a (9,7) SWCNT, as
optimized at the semiempirical level using the PM6 Hamiltonian with
D3H4 correction (top) and using the PM7 Hamiltonian (bottom). (b)
Qualitative models of possible stacking of SQ molecules in different
diameter SWCNTs, based on the calculated intermolecular distances
in π-stacked and head-to-tail SQ dimers. Top to bottom: 1D array
of SQ in a (9,7) SWCNT; tilted single-file SQ array and double-file
array with small slip-shift between π-stacked monomers are both
plausible structures in a (10,9) SWCNT; and a staggered double-file
array of SQ molecules in a (12,8) SWCNT would explain the even larger
redshift. In panel a, spheres represent atom’s standard van
der Waals radii.