By varying precursor structure, core/shell and alloyed nanocrystal synthesis are performed in a single synthetic step.

For quantum-confined nanomaterials, size dispersion causes a static broadening of spectra that has been difficult to measure and invalidates all-optical methods for determining the maximum photovoltage that an excited state can generate. Using femtosecond two-dimensional (2D) spectroscopy to separate size dispersion broadening of absorption and emission spectra allows a test of single-molecule generalized Einstein relations between such spectra for colloidal PbS quantum dots. We show that 2D spectra and these relations determine the thermodynamic standard chemical potential difference between the lowest excited and ground electronic states, which gives the maximum photovoltage. Further, we find that the static line broadening from many slightly different quantum dot structures allows single-molecule generalized Einstein relations to determine the average single-molecule linewidth from Stokes’ frequency shift between ensemble absorption and emission spectra.

The heterogeneous growth of inorganic shells on seed nanocrystals is used to synthesize heterostructured nanocrystals such as core@shell quantum dots for applications ranging from biological imaging to solid-state lighting. Control over shelling reactions can be achieved through continuous or layer-by-layer growth methods that are tedious and time-consuming, particularly for the growth of complex, multishell heterostructures. Here, we leverage high-throughput synthesis along with a library of precursors with tunable reactivity to develop a comprehensive understanding of the role of precursor reactivity, ligands, and temperature in one-step, seeded growth reactions on CdSe quantum dots. These experiments reveal a narrow range of precursor reactivity and monomer solubility that fosters the uniform, purely heterogeneous growth of shell material on the seed particles. This narrow "ideal growth" regime in experimental parameter space is sandwiched between opposing regimes that lead to secondary nucleation or ripening during growth. We also report that, at high concentrations of tri-n-octylphosphine, shell growth reactions exhibit "digestive ripening", in which size distributions focus while particles dissolve. Coupled with kinetic simulations, these experiments reveal that the precursor reaction rate and monomer solubility are highly interdependent shell growth parameters that determine the balance between secondary nucleation and ripening. In contrast, the surface energy determines the evolution of the size and polydispersity of the heterostructures over time.

Nicotinic acetylcholine receptors are a diverse set of ion channels that are essential to everyday brain function. Contemporary research studies selective activation of individual subtypes of receptors, with the hope of increasing our understanding of behavioral responses and neurodegenerative diseases. Here, we aim to expand current binding models to help explain the specificity seen among three activators of α4β2 receptors: sazetidine-A, cytisine, and NS9283. Through mutational analysis, we can interchange the activation profiles of the stoichiometry-selective compounds sazetidine-A and cytisine. In addition, mutations render NS9283—currently identified as a positive allosteric modulator—into an agonist. These results lead to two conclusions: (1) occupation at each primary face of an α subunit is needed to activate the channel and (2) the complementary face of the adjacent subunit dictates the binding ability of the agonist.

We report the color conversion performance of amber and red emitting quantum dots on InGaN solid state lighting (SSL) light emitting diode (LED) packages. Spherical quantum well (SQW) architectures (CdS/CdSe1-xSx/CdS) were finely adjusted using a library of thio-and selenourea synthesis reagents and high throughput synthesis robotics. CdS/CdSe1-xSx particles with narrow luminescence bands were coated with thick CdS shells (thickness = 1.4 -7.5 nm) to achieve photoluminescence quantum yields (PLQY) up to 88% at amber and red emission wavelengths (max = 600 -642nm, FWHM < 45 nm). The photoluminescence from SQWs encapsulated in silicone and deposited on LED packages was monitored under accelerated aging conditions (oven temperature = 85 C, relative humidity = 5 -85%, blue optical power density = 3 -45 W/cm 2 ) by monitoring the red photon output over several hundred hours of continuous operation. Growth of a ZnS shell on the SQW surface increases the stability under long-term operation but also reduces the PLQY, especially of SQWs with thick CdS shells. The results illustrate that the outer ZnS shell layer is key to optimizing the PLQY and the long-term stability of QDs during operation on SSL packages.

In this talk I will describe a IV-VI and II-VI quantum dot synthesis platform based on substituted thio-and selenourea precursors, in which changing the precursor conversion kinetics leads to predictable changes in the final size and number of nanocrystals. By monitoring the synthesis with in situ absorption spectroscopy, small-and wide-angle X-ray scattering, and high-throughput robotic methods, we have begun to elucidate nucleation thresholds, size-dependent growth rates, and fundamental differences between analogous materials. I will discuss the implications of these insights for quantum dot-based solid-state lighting, which requires kinetically trapped CdSe/CdS heterostructures to obtain desirable luminescence properties.

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