Brightening of Dark Excitons in Single-Walled Carbon Nanotubes: Investigation by Many-Body Green's Function Theory

Optical excitations of the hybrids, which are assembled by coupling single-walled carbon nanotubes (SWCNTs) with organic molecules through van der Waals interactions, are studied using ab initio many-body Green's function theory. We take the semiconducting (7, 0) SWCNT, the squarylium and oligothiophene molecules as the example. The E_11 and E_22 absorption peaks of the (7, 0) tube can be redshifted by tens of meV. Most importantly, the lowest dark exciton of the (7, 0) tube at the lower-energy side of E_11 can be brightened by the interaction between the nanotube and molecules. Position of this new satellite absorption peak is influenced by the type of adsorbed molecule. These findings may be useful for tuning the emission energy and emission efficiency of CNTs.