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The effect of chemical-composition modification on the chiroptical property of chiral organic ammonium cation-containing organic inorganic hybrid perovskite (chiral OIHP) is investigated. Varying the mixing ratio of bromide and iodide anions in Sor R-C 6 H 5 CH 2 (CH 3 )NH 3 ) 2 PbI 4(1−x) Br 4x modifies the band gap of chiral OIHP, leading to a shift of the circular dichroism (CD) signal from 495 to 474 nm. However, it is also found that an abrupt crystalline structure transition occurs, and the CD signal is turned off when iodide-determinant phases are transformed into the bromide-determinant phase. To obtain CD in the wavelength range where the bromide-determinant phase is supposed to exhibit chiroptical activity, that is, <474 nm, Sor R-C 12 H 7 CH 2 (CH 3 )NH 3 with a larger spacer group can be adopted; thus, the CD signal can be further blue-shifted to ∼375 nm. Here, we show that chemical-composition modification of chiral OIHP affects the chiroptical properties of chiral OIHP in two ways: (1) tuning the wavelength of CD by modulating the excitonic band structure and (2) switching the CD on and off by inducing a crystalline-structure change. These properties can be utilized for structural engineering of high-performance chiroptical materials for spin-polarized light-emitting devices and polarization-based optoelectronics.

Mesoscale CdTe helices with near-unity enantiomeric excess offer insight into design rules for chiroptical semiconductor materials.

Photon-to-matter chirality transfer offers both simplicity and universality to chiral synthesis but its efficiency is typically low for organic compounds. New pathways for imposing chiral bias during chemical process are essential for a variety of technologies from medicine to informatics as well as for fundamental science. Strong optical activity of inorganic nanoparticles (NPs) afford photosynthetic routes to chiral superstructures using circularly polarized photons. Plasmonic NPs are especially promising candidates for such reactions but realization and adequate interpretation of light-driven synthesis of chiral nanostructures in light-driven processes was more challenging than for semiconductor NPs. The process also requires unconventional approaches for the quantification of chiral products. Here we show that illumination of nanoscale colloidal dispersions with circularly polarized light induces the formation of chiral nanostructures 10-15 nm in diameter. Despite their seemingly irregular shape, the resulting nanocolloids showed circular dichroism (CD) spectra with opposite polarity after exposure to photons with left-and right circular polarization. The sign and spectral position of the experimental CD peaks of

A large variety of nanoparticles were synthesized during the last 25 years and are used now as “building blocks” for a variety of materials. Bottom-up solution processing of devices emerged as a promising direction of their technological applications because this method can (a) utilize intrinsic ability of nanocolloids to self-organize, (b) reduce high energy and equipment cost of device manufacturing, and (c) impart new functionalities to electronic devices. However the technological impact of solution processable semiconductor materialsalthough potentially considerablehas been so far limited because of the long-standing dilemma between the need for effective colloidal stabilization of nanoparticles and effective charge transport. Surfactants and other organic materials being used to synthesize and/or disperse nanocolloids introduce a barrier for charge transport between the particles. Although these barriers do make it impossible to use them in electronic devices, they certainly make it more difficult. In this review, we look into the latest progress in the solution processable devices and methods to produce electrically conductive thin films from nanoscale dispersions. We are specifically interested in the understanding of the prospects of self-assembly to facilitate charge transport and nanoscale connectivity during solution processing. The updated theoretical description of charge transport in nanoparticle solids and similar nanomaterials is also given. It includes consideration of the key mechanisms such as tunneling and cotunneling, as well as key electrical parameters characterizing transport of electrons through the surfactant-related barriers, such as coupling energy and Coulombic charging energy. Manifestations of these mechanisms in different electronic materials made from nanoparticles, nanowires, nanotubes, and nanosheets and their relative advantages and disadvantages are also discussed. We conclude the topic with a brief description of new opportunities and approaches to improve charge transport in solution processed materials from nanoscale dispersions.

Unique optical, electrical, and mechanical properties of continuous semiconductor helices with nanoscale and mesoscale dimensions represent a previously unexplored materials platform for various applications requiring near-infrared (NIR) optical activity. However, current methods of their synthesis limit the spectrum of chiral geometries, charge transport, and spectral response. Furthermore, the requirements of nearly perfect enantioselectivity, high uniformity, and high yield need to be attained as well. Here, we show that continuous semiconductor helices with tunable spectral response and high monodispersity can be made via self-assembly of semiconductor nanoparticles (NPs). Unraveling the interdependent effects of solvent, pH, ligand density, and coordination bridges between NPs allowed us to maximize the chiral bias for face-to-face particle–particle interactions, control of the geometry of the helices, and increase assembly efficiency by 3 orders of magnitude. The self-limiting nature of NP association results in consistency of their geometries over the entire synthetic ensemble. The helices show chiroptical activity across a broad range of wavelengths from 300 to 1300 nm, and the maximum/sign of their polarization rotation in NIR part can be modulated by varying their pitch. The method described in this study can be extended to chiral semiconductor materials from a variety of other NPs and their combinations.

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We describe the facile synthesis of stable gold nanoparticle clusters densely functionalized with DNA (DNA-AuNP clusters) using dithiothreitol and monothiol DNA and their thermally reversible assembly properties. The size of the clusters exhibits a very narrow distribution and can be easily controlled by adjusting the stoichiometry of dithiothreitol and DNA, leading to a variety of colors due to the surface plasmon resonance of the AuNP clusters. Importantly, the DNA-AuNP clusters exhibit highly cooperative melting properties with distinctive and diverse color changes depending on their size. The selective and sensitive colorimetric detection of target sequences was demonstrated based upon the unique properties of the DNA-AuNP clusters.