title: Effects of surface-passivating ligands and ultrasmall CdSe nanocrystal size on the delocalization of exciton confinement.
abstract: Here we report an unprecedentedly large and controllable decrease in the optical band gap (up to 107 nm, 610 meV) of molecule-like ultrasmall CdSe nanocrystals (diameters ranging from 1.6 to 2.0 nm) by passivating their surfaces with conjugated ligands (phenyldithiocarbamates, PDTCs) containing a series of electron-donating and -withdrawing functional groups through a ligand-exchange reaction on dodecylamine (DDA)-coated nanocrystals. This band-edge absorption shift is due to the delocalization of the strongly confined excitonic hole from nanocrystals to the ligand molecular orbitals and not from nanocrystal growth or dielectric constant effects. (1)H NMR analysis confirmed that the nanocrystal surface contained a mixed ligation of DDA and PDTC. The effects of the nanocrystal size on the extent of exciton delocalization were also studied and found to be smaller for larger nanocrystals. Modulating the energy level of ligand-passivated ultrasmall nanocrystals and controlling the electronic interaction at the nanocrystal-passivating ligand interface are very important to the fabrication of solid-state devices.
authors.affiliation: Department of Chemistry and Chemical Biology and ‡Integrated Nanosystems Development Institute, Indiana University-Purdue University Indianapolis , Indianapolis, Indiana 46202, United States.
authors.forename: Meghan B
authors.initials: MB
authors.lastname: Teunis
authors.forename: Sukanta
authors.initials: S
authors.lastname: Dolai
authors.forename: Rajesh
authors.initials: R
authors.lastname: Sardar