Wonseok Lee

Recently, lead halide perovskite (LHP) materials have shown potential for many optoelectronic applications. However, the structural instability and toxicity concerns necessitated robust and heavy-metal-free alternatives. We report a synthetic route to Cs2AgInCl6 double-perovskite nanocrystals (DP NCs) that have the crystal structure replacing two lead ions in LHP by a pair of silver and indium ions. Cubic-shaped Cs2AgInCl6 DP NCs were obtained with a narrow size distribution, which showed superior stability against moisture that rivaled core–shell-structured CdS/ZnS NCs. Cs2AgInCl6 DP NCs showed discrete optical properties: (i) multiple absorbing states that resolved the parity-forbidden band-edge transition at 3.33 eV and next—following higher order parity—allowed transition at 4.88 eV and (ii) multiple emission states that consisted of the band edge emission at 350 nm and emissions from defective states that peaked at 395 nm. The synthetic route was further exploited for isovalent doping with lanthanide ions, which yielded Yb-doped, Er-doped, and Yb/Er-codoped Cs2AgInCl6 DP NCs. The characteristic f–f transition emissions were observed in infrared at 996 nm for Yb3+ and at 1537 nm for Er3+ dopants.

Recent technological advances have expanded fluorescence (FL) imaging into the second near-infrared region (NIR-II; wavelength = 1000-1700 nm), providing high spatial resolution through deep tissues. However, bright and compact fluorophores are rare in this region, and sophisticated control over NIR-II probes has not been fully achieved yet. Herein, we report an enzyme-activatable NIR-II probe that exhibits FL upon matrix metalloprotease activity in tumor microenvironment. Bright and stable PbS/CdS/ZnS core/shell/shell quantum dots (QDs) were synthesized as a model NIR-II fluorophore, and activatable modulators were attached to exploit photoexcited electron transfer (PET) quenching. The quasi type-II QD band alignment allowed rapid and effective FL modulations with the compact surface ligand modulator that contains methylene blue PET quencher. The modulator was optimized to afford full enzyme accessibility and high activation signal surge upon the enzyme activity. Using a colon cancer mouse model, the probe demonstrated selective FL activation at tumor sites with 3-fold signal enhancement in 10 min. Optical phantom experiments confirmed the advantages of the NIR-II probe over conventional dyes in the first near-infrared region.

As an alternative to lead halide perovskites, various types of lead-free perovskites have been recently studied for optoelectronic materials. This paper reports the synthesis of highly phase-pure Cs2NaBiX6 (X = Cl, Br) double perovskite (DP) nanocrystals (NCs). They show characteristic absorption features of sharp and discrete peaks mostly originating from the Bi3+ s–p transition (6s2 → 6s1p1) in [BiX6]3– units within the crystal lattice of the elpasolite structure. Such unique optical properties are attributed to the non-bonding character of electropositive sodium and electronically isolated [BiX6]3– units in crystals. The shape of Cs2NaBiX6 NCs could be quantitatively controlled by adjusting the reaction temperature. Reaction temperatures above 180 °C favor development of a cuboctahedral (CO) shape, whereas development of a cuboidal (CB) shape is favored below 170 °C. CB NCs can be subsequently converted to CO NCs by heating to 200 °C. The CO NCs promote the growth of heterostructure adducts on the (111) facets; these adducts could be posteliminated by etching. Mn-doped Cs2NaBiCl6 NCs are synthesized; they show efficient energy transfer from the NC host to the dopants. The synthesis and shape control of Cs2NaBiX6 NCs and Mn-doped Cs2NaBiCl6 NCs could expand a new class of lead-free DP NCs applicable to optoelectronic applications.

In this study, we designed and synthesized far-red- and near-infrared-emitting Cu-doped InP-based quantum dots (QDs), and we also demonstrated their highly specific and sensitive biological imaging ability. Cu-doped InP/ZnS (core/shell) QDs were prepared using the hot colloidal synthesis method in the organic phase. The ZnS shell passivates the surface and improves the photoluminescence (PL) intensity. However, the InP : Cu/ZnS (core : dopants/shell) QDs, which were obtained after the Cu dopant was incorporated into bare InP QDs, followed by ZnS shell coating, had relatively low PL intensities (maximum PL quantum yield (QY) was only ∼16%) presumably due to the formation of defect sites in the InP-core QDs caused by dopant migration from the InP core to the ZnS shell. We prepared high-quality InP/ZnS : Cu/ZnS (core/shell : dopant/outer-shell) QDs, where thin ZnS shell layers were grown on bare InP QDs prior to Cu ion doping to prevent dopant migration and obtained PL QYs as high as 40%. The native hydrophobic ligands of the as-synthesized Cu-doped QDs were replaced with hydrophilic ligands including dihydrolipoic acid and a zwitterionic ligand, which rendered the QDs water-soluble. These QDs exhibited remarkable colloidal stabilities over a wide pH range, with hydrodynamic diameters less than 10 nm. Modified QD surfaces can also be used in conjugation with other functional moieties to apply highly specific and sensitive imaging probes with very low background levels. As a proof-of-concept study, we successfully demonstrated the selective imaging of streptavidin beads with biotin-conjugated QDs. These decorated Cu-doped InP/ZnS (core/shell) QDs are promising biological-probe candidates for imaging and assaying with reduced concerns regarding toxicity.

Abstract We have used Fourier transform infrared absorption spectroscopy to study the molecular motions of hexa(hexylthio)triphenylene as a function of temperature. Our measurements show pronounced changes in the CH3 stretching mode frequencies at the K → H transition. (The H phase displays long range incommensurate helical order). However, the CH2 stretching mode frequencies show much less variation with temperature, suggesting that only the ends of the alkyl tails undergo much change in the different phases. The CH bending and benzene stretching vibrations show a change in the frequency-temperature dependence at both the K → H and the H → Dhd transitions. There is no observable change in the spectrum in going from the Dnd to the 1 phase. We also present detailed syntheses for hexa(hexyl-thio)triphenylene and its C5 and C7 homologs. Physics Abstracts Classification: 64.70.M, 61.30.E, 33.20.E, 78.30.