S1. Spectroscopy characterization1 H NMR and FTIR characterization. The 1 H NMR spectra were obtained with a Bruker AVANCE III 500 instrument at 500 MHz frequency. Typically ~10-15 mg of purified sample were dissolved in 0.6 mL of chloroform-d at room temperature. A minimum of 1024 scans were collected with a 30° pulse angle, 3.17 sec of acquisition, and 3 sec of relaxation. All data were plotted via TOPSPIN 2.1 software. The FTIR measurements were taken using a Thermo Nicolet IS10 FT-IR spectrometer. For FT-IR analysis, samples were prepared by placing a 10 µL dissolved sampled on a KBr salt plate. A minimum of 128 scan was collected and all data were processed using Omnic FTIR software.Energy dispersive X-ray (EDX) analysis. EDX analysis was performed using a Hitachi S-4700 field-emision scanning electron microscope. The measurements were conducted at a pressure <5 x10 -9 Torr. For XPS analysis, the CH 3 NH 3 PbBr 3 quantum wires were drop-casted on a piranha-cleaned silicon wafer inside a N 2 filled glove box, and the solution was allowed to evaporate at room temperature. The piranha-cleaned silicon wafer had been washed with a copious amount of Nanopure water and ethanol, and then dried in a vacuum oven at 120 °C over night. The XPS analysis was performed for two different batches of CH 3 NH 3 PbBr 3 quantum wires and five randomly selected area. (Warning: piranha solution is highly reactive and must be handled with extreme caution. It reacts violently with organic materials and may not be stored in tightly closed vessels). X-ray photoelectron spectroscopy (XPS) analysis.All XPS spectra were collected on a Kratos Axis Ultra DLD system with a Mg anode at 1253.6 eV and X-ray power of 150 W. A charge neutralizer was used to prevent charging. The survey scans were collected over binding energies of 0-1000 eV with a 80 eV pass energy. For high resolution scans of Pb(4f), Br(3d), and N(1s), a 20 eV pass energy was used. All data were collected so that the C 1s line was shifted to 284.6 eV. The samples were prepared as described for EDX analysis. Here, two different batches of CH 3 NH 3 PbBr 3 quantum wires were analyzed over five randomly selected areas in each.Powder X-ray diffraction (XRD) analysis. Wide-angle XRD was recorded on a Rigaku MiniFlex™ II (Cu Kα) instrument. Sample was prepared by dropcasting the purified quantum wires on a piranha cleaned glass coverslips. S2. Characterization data (Fig. S1 to Fig. S13)

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.

This paper reports large bathochromic shifts of up to 260 meV in both the excitonic absorption and emission peaks of oleylamine (OLA)-passivated molecule-like (CdSe) nanocrystals caused by postsynthetic treatment with the electron accepting Cd(OCPh) complex at room temperature. These shifts are found to be reversible upon removal of Cd(OCPh) by N,N,N',N'-tetramethylethylene-1,2-diamine. H NMR and FTIR characterizations of the nanocrystals demonstrate that the OLA remained attached to the surface of the nanocrystals during the reversible removal of Cd(OCPh). On the basis of surface ligand characterization, X-ray powder diffraction measurements, and additional control experiments, we propose that these peak red shifts are a consequence of the delocalization of confined exciton wave functions into the interfacial electronic states that are formed from interaction of the LUMO of the nanocrystals and the LUMO of Cd(OCPh), as opposed to originating from a change in size or reorganization of the inorganic core. Furthermore, attachment of Cd(OCPh) to the OLA-passivated (CdSe) nanocrystal surface increases the photoluminescence quantum yield from 5% to an unprecedentedly high 70% and causes a 3-fold increase of the photoluminescence lifetime, which are attributed to a combination of passivation of nonradiative surface trap states and relaxation of exciton confinement. Taken together, our work demonstrates the unique aspects of surface ligand chemistry in controlling the excitonic absorption and emission properties of ultrasmall (CdSe) nanocrystals, which could expedite their potential applications in solid-state device fabrication.

Systematic tailoring of nanocrystal architecture could provide unprecedented control over their electronic, photophysical, and charge transport properties for a variety of applications. However, at present, manipulation of the shape of perovskite nanocrystals is done mostly by trial-and-error-based experimental approaches. Here, we report systematic colloidal synthetic strategies to prepare methylammonium lead bromide quantum platelets and quantum cubes. In order to control the nucleation and growth processes of these nanocrystals, we appropriately manipulate the solvent system, surface ligand chemistry, and reaction temperature causing syntheses into anisotropic shapes. We demonstrate that both the presence of chlorinated solvent and a long chain aliphatic amine in the reaction mixture are crucial for the formation of ultrathin quantum platelets (∼2.5 nm in thickness), which is driven by mesoscale-assisted growth of spherical seed nanocrystals (∼1.6 nm in diameter) through attachment of monomers onto selective crystal facets. A combined surface and structural characterization, along with small-angle X-ray scattering analysis, confirm that the long hydrocarbon of the aliphatic amine is responsible for the well ordered hierarchical stacking of the quantum platelets of 3.5 nm separation. In contrast, the formation of ∼12 nm edge-length quantum cubes is a kinetically driven process in which a high flux of monomers is achieved by supplying thermal energy. The photoluminescence quantum yield of our quantum platelets (∼52%) is nearly 2-fold higher than quantum cubes. Moreover, the quantum platelets display a lower nonradiative rate constant than that found with quantum cubes, which suggests less surface trap states. Together, our research has the potential both to improve the design of synthetic methods for programmable control of shape and assembly and to provide insight into optoelectronic properties of these materials for solid-state device fabrication, e.g., light-emitting diodes, solar cells, and lasing materials.

Organic-inorganic hybrid perovskites, direct band-gap semiconductors have shown tremendous promise for optoelectronic device fabrication. We report the first colloidal synthetic approach to prepare ultrasmall (~1.5 nm diameter), white light emitting, organic-inorganic hybrid perovskite nanoclusters. The nearly pure white-light emitting ultrasmall nanoclusters were obtained by selectively manipulating the surface chemistry (passivating ligands and surface trap-states) and controlled substitution of halide ions. The nanoclusters displayed a combination of band-edge and broadband photoluminescence properties, covering a major part of the visible region of the solar spectrum with unprecedentedly large quantum yields of ~12% and photoluninescence lifetime of ~20 ns. The intrinsic white light emission of perovskite nanoclusters makes them ideal and low cost hybrid nanomaterials for solid-state lighting applications.The ever-increasing global demand for energy drives the need to discover highly efficient materials capable of saving energy in solid-state lighting (SSL) applications, such as light-emitting diodes (LEDs). 1,2 In this context, pure white-light emitting materials, and their subsequent uses in LED fabrication, will be a most effective way to reduce global power consumption. Currently, white-light LEDs are prepared by: (i) mixing single wavelength emitting organic phosphors, 3 and (ii) constructing multi-layer films composed of blue, green, and red color emitting semiconductor quantum dots (QDs). 4,5 However, the self-absorption process between different organic phosphors reduces device efficiency, a similar device characteristic that has also been observed for QD-based LEDs. Ultrasmall semiconductor nanoclusters (e.g., CdSe) display white-light, but they require expensive, complicated and high temperature synthetic methods. [6][7][8] Recently, white-light emitting bulk organic-inorganic perovskites were synthesized, 9,10 which would not only expand SSL research but also facilitate inexpensive LED fabrication. Scheme 1. Schematic Presentation of the Synthesis of White-Light Emitting Organolead Bromide Perovskite NanoclustersIn this communication, we report the first colloidal synthetic method to prepare white-light emitting, ultrasmall (~1.5 nm diameter) methylammonium lead bromide (MAPbBr3) perovskite nanoclusters (PNCs). Their synthesis is outlined in Scheme 1 and the detailed procedure is provided in the Electronic Supplementary Information (ESI) file. These PNCs display a combination of band-edge and broadband photoluminescence (PL) with a quantum yield (QY) of ~5% and PL lifetime of ~7 ns. We hypothesize that the broad emission properties originate from the presence of surface-related midgap trap-states. Furthermore, we showed selective manipulation of band-gap and trap-states via the preparation of mixed halide (MAPbClxBr3-x) PNCs through controlled anion exchange reactions enhanced both QY and PL lifetime at least two-fold. We believe these ultrasmall PNCs will provide fundamentally important informati...