The diameter of QD4 measured on aC (Fig. , see also Figure ) showed average diameters of 2.49, 2.46, and 2.59 nm for 1, 2, and OA•MA•QD4 (3), respectively (Fig. ), consistent with the QD4 structure (Fig. ). QD4 accounts for 95%, 91%, but only 71% of 1, 2, and 3, respectively. As such, we determined that the distribution observed for 1 and 2, ranging from 1.8 nm to 3.1 nm was consistent with a measurement distribution of uniform QD4 (see Supplementary Note 2). 3 was contaminated by as much as 24% of larger QDs, which is corroborated by the emission data shown in Fig. . X-Ray characterization of 1 and 2 is shown in the Figure . Clear periodicity is observed in the long order domain (2 to 10°) which corresponds to the self-assembly of uniform nanoclusters into a highly regular superlattice. We have estimated the superlattice parameter to be between 3.8 and 3.9 nm. Assuming an Oleylamine length of 1.5 nm as previous literature suggests , we obtain a nanocluster edge length of 2.3 to 2.4 nm, highly consistent with the selfassembly of QD4. 1 and 2 in toluene emit at 453 and 463 nm with narrow FWHM of 14.9 and 14.7 nm, respectively. PLQY values of 95.6% and 97% are also excellent with some specimens reaching 100%. The high PLQY of 1 originates from fast radiative decay (kr = 10.6 ´ 10 7 s -1 ) and slow nonradiative decay (knr = 0.5 ´ 10 7 s -1 , see Figure for details). The PLQY of 3 was poor and its reproducibility was low (average 24%), although FWHM at 454 nm was narrow (15 nm). The long tail toward green emission is due to contamination by QD5 and QD6 as shown by the red lines in Fig. and. MLA•QD4 is stable under shelf storage, UV irradiation, and electroluminescence device setup. 1, with an initial PLQY of 97%, showed little sign of deterioration over 30 days under air at 5 °C in toluene containing 4 mg/mL MLA (Fig. , blue triangles). It is less stable without added MLA (i.e., in pure toluene) at 5 °C (blue circles), suggesting an equilibrium that causes loss of the MLA ligand (see Figure ). The half-life of 2 is much longer, approaching 40 days in pure toluene (green circles). The difference between 1 and 3 was more striking under UV irradiation (Fig. ). The 455-nm emission of 1 slightly decreased to 95% after 10 h, whereas that of 3 decreased quickly to half within 2 h with emission shifted to green (530 nm, indicating crystal fusion), probably because the OA ligand dissociates more easily than the multidentate MLA ligand (Figure ). Such a dissociation equilibrium also accounts for the low chemical stability of OA-based QDs. This emission shifting indicated the fusion of 3 into large nanoparticles.