Reversible Exchange of L-Type and Bound-Ion-Pair X-Type Ligation on Cadmium Selenide Quantum Belts.

CdSe quantum belts of composition {CdSe[n-octylamine]0.53} and protic acids HX (X = Cl, Br, NO3, acetate (OAc), and benzoate (OBz)) react to exchange the L-type amine ligation to bound-ion-pair X-type ligation. The latter ligation has X- anions bound to the nanocrystal surfaces and closely associated LH+ counter-cations (protonated n-octylamine or tri-n-octylphosphine (TOP) to balance the surface charges. The compositions of the exchanged QBs are {CdSe[Br]0.44[n-octylammonium]0.41}, {CdSe[NO3]0.10[TOPH]0.12}, {CdSe[OBz]0.08[n-octylammonium]0.02[TOPH]0.06}, and {CdSe[OAc]0.16[n-octylammonium]0.02[TOPH]0.14}. (The HCl-exchanged QBs are insufficiently stable for elemental analysis.) The bound-ion-pair X-type ligation is fully reversed to L-type n-octylamine ligation in the cases of X = NO3, acetate, and benzoate. The ligand exchanges are monitored by absorption spectroscopy, and the exchanged, bound-ion-pair X-type ligated nanocrystals are characterized by a range of methods.