Endohedral terthiophene in zigzag carbon nanotubes:: Density functional calculations

The inclusion and encapsulation of terthiophene (T3) molecules inside zigzag single-walled carbon nanotubes (CNT's) is addressed by density functional calculations. We consider the T3 molecule inside six semiconducting CNT's with diameters ranging approximately from 8 to 13 A. Our results show that the T3 inclusion process is exothermic for CNT's with diameters larger than 9 A. The highest energy gain is found to be of 2 eV, decreasing as the CNT diameter increases. This notable effect of stabilization is attributed to the positively charged CNT inner space, as induced by its curvature, which is able to accommodate the neutral T3 molecule. The band structure of the T3@CNT system shows that T3 preserves its electronic identity inside the CNT's, superimposing their molecular orbitals onto the empty CNT band structure without hybridization. Our results predict that the electronic states added by the T3 molecules would give rise to optical effects and nonradiative relaxation from excited states.