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)

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.

ABSTRACT:We have designed a new non-phosphinated reaction pathway, which includes synthesis of a new, highly reactive Se-bridged organic species (chalcogenide precursor), to produce bright white light-emitting ultrasmall CdSe nanocrystals of high quality under mild reaction conditions. The detailed characterization of structural properties of the selenium precursor through combined 77 Se NMR and laser desorption ionization-mass spectrometry (LDI-MS) provided valuable insights into Se release and delineated the nanocrystal formation mechanism at the molecular level. The 1 H NMR study showed that the rate of disappearance of Se-precursor maintained a single-exponential decay with a rate constant of 2.3 x 10 -4 s -1 at room temperature. Furthermore, the combination of LDI-MS and optical spectroscopy was used for the first time to deconvolute the formation mechanism of our bright white light-emitting nanocrystals, which demonstrated initial formation of a smaller key nanocrystal intermediate (CdSe)19. Application of thermal driving force for destabilization resulted in (CdSe)n nanocrystal generation with n = 29-36 through continuous dissolution and addition of monomer onto existing nanocrystals while maintaining a living-polymerization type growth mode. Importantly, our ultrasmall CdSe nanocrystals displayed an unprecedentedly large fluorescence quantum yield of ~27% for this size regime (<2.0 nm diameter). These mixed oleylamine and cadmium benzoate ligand-coated CdSe nanocrystals showed a fluorescence lifetime of ~90 ns, a significantly large value for such small nanocrystals, which was due to delocalization of the exciton wavefunction into the ligand monolayer. We believe our findings will be relevant to formation of other metal chalcogenide nanocrystals through expansion of the understanding and manipulation of surface ligand chemistry, which together will allow the preparation of "artificial solids" with high charge conductivity and mobility for advanced solid-state device applications.3

Aqueous mixtures of poly(ethylene glycol) (PEG) of different compositions offer widely varying physicochemical properties that may support porphyrin aggregation. Aggregation behavior of a common water-soluble porphyrin, meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS), is investigated within aqueous PEG mixtures constituted of PEGs of average molecular weights 200 (PEG200), 400 (PEG400), 600 (PEG600), and 1000 (PEG1000) using UV-vis molecular absorbance, steady-state fluorescence, and resonance light scattering techniques. No aggregation of TPPS is observed in neat PEGs; addition of 10 wt % water to PEG at pH 1.0 is found to trigger TPPS into significant J-aggregation. The J-aggregation is observed to be most efficient within an aqueous mixture of 90 wt % PEG1000 at pH 1.0. The effect of ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]), as additives on the J-aggregation efficiency of TPPS within aqueous mixtures of PEG400 at pH 1.0 is investigated and compared with the effect of salts NaCl, NaPF(6), and NaBF(4) as additives on the J-aggregation of TPPS under the same conditions. In an aqueous mixture of 10 wt % PEG400 at pH 1.0, ionic liquids are observed to increase the J-aggregation efficiency more than the salts at lower concentrations. The efficiency of J-aggregation decreases upon further addition of [bmim][BF(4)] due to reduced dissociation of this ionic liquid in the mixture. While the three salts show limited solubility, the two ionic liquids are completely miscible in a 90 wt % PEG400 mixture in water at pH 1.0. The J-aggregation efficiency of TPPS increases rapidly and reaches a maximum before decreasing gradually as more and more ionic liquid is added to the mixture. The results draw attention to the unique dual role of ionic liquids as additives in affecting the J-aggregation of TPPS within aqueous mixtures of PEG as well as to their proficiency over common salts in J-aggregation.

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...