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]} and protic acids HX (X = Cl, Br, NO, 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][n-octylammonium]}, {CdSe[NO][TOPH]}, {CdSe[OBz][n-octylammonium][TOPH]}, and {CdSe[OAc][n-octylammonium][TOPH]}. (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 = NO, 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.