  Despite many theoretical schemes, the direct experimental observation of
supramolecular control on band gap opening in single-walled carbon nanotubes
(SWNT) is still lacking. We report experimental and theoretical demonstration
of metal to semiconductor transition with precisely measured large band gap in
SWNTs due to the wrapping of mannose functionalized poly (propyl ether imine)
dendrimer (DM) molecules. Semiconductor behaviour of SWNT-DM complex is
comprehensively established with a band gap value of ~ 0.45 eV measured using
scanning tunnelling spectroscopy (STS), ionic liquid top gated field effct
transistor (FET) characteristics and Raman spectroscopy. Further, a validated
molecular picture of SWNT-DM complex obtained from fully atomistic molecular
dynamic (MD) simulations was used to carry out ab-initio density functional
theory (DFT) and GW calculations of the electronic structure, evaluating
experimentally estimated band gap value. We attribute this large band gap
opening in SWNTs to the complexation induced asymmetric strain developed in the
carbon-carbon bond length.
