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.