Electronic Processes within Quantum Dot-Molecule Complexes.

The subject of this review is the colloidal quantum dot (QD) and specifically the interaction of the QD with proximate molecules. It covers various functions of these molecules, including (i) ligands for the QDs, coupled electronically or vibrationally to localized surface states or to the delocalized states of the QD core, (ii) energy or electron donors or acceptors for the QDs, and (iii) structural components of QD assemblies that dictate QD-QD or QD-molecule interactions. Research on interactions of ligands with colloidal QDs has revealed that ligands determine not only the excited state dynamics of the QD but also, in some cases, its ground state electronic structure. Specifically, the article discusses (i) measurement of the electronic structure of colloidal QDs and the influence of their surface chemistry, in particular, dipolar ligands and exciton-delocalizing ligands, on their electronic energies; (ii) the role of molecules in interfacial electron and energy transfer processes involving QDs, including electron-to-vibrational energy transfer and the use of the ligand shell of a QD as a semipermeable membrane that gates its redox activity; and (iii) a particular application of colloidal QDs, photoredox catalysis, which exploits the combination of the electronic structure of the QD core and the chemistry at its surface to use the energy of the QD excited state to drive chemical reactions.

Powering a CO2 Reduction Catalyst with Visible Light through Multiple Sub-picosecond Electron Transfers from a Quantum Dot.

Photosensitization of molecular catalysts to reduce CO2 to CO is a sustainable route to storable solar fuels. Crucial to the sensitization process is highly efficient transfer of redox equivalents from sensitizer to catalyst; in systems with molecular sensitizers, this transfer is often slow because it is gated by diffusion-limited collisions between sensitizer and catalyst. This article describes the photosensitization of a meso-tetraphenylporphyrin iron(III) chloride (FeTPP) catalyst by colloidal, heavy metal-free CuInS2/ZnS quantum dots (QDs) to reduce CO2 to CO using 450 nm light. The sensitization efficiency (turnover number per absorbed unit of photon energy) of the QD system is a factor of 18 greater than that of an analogous system with a fac-tris(2-phenylpyridine)iridium sensitizer. This high efficiency originates in ultrafast electron transfer between the QD and FeTPP, enabled by formation of QD/FeTPP complexes. Optical spectroscopy reveals that the electron-transfer processes primarily responsible for the first two sensitization steps (FeIIITPP → FeIITPP, and FeIITPP → FeITPP) both occur in <200 fs.

Two-color single-photon emission from InAs quantum dots: toward logic information management using quantum light.

In this work, we propose the use of the Hanbury-Brown and Twiss interferometric technique and a switchable two-color excitation method for evaluating the exciton and noncorrelated electron-hole dynamics associated with single photon emission from indium arsenide (InAs) self-assembled quantum dots (QDs). Using a microstate master equation model we demonstrate that our single QDs are described by nonlinear exciton dynamics. The simultaneous detection of two-color, single photon emission from InAs QDs using these nonlinear dynamics was used to design a NOT AND logic transference function. This computational functionality combines the advantages of working with light/photons as input/output device parameters (all-optical system) and that of a nanodevice (QD size of ∼ 20 nm) while also providing high optical sensitivity (ultralow optical power operational requirements). These system features represent an important and interesting step toward the development of new prototypes for the incoming quantum information technologies.

Electrostatic Control of Excitonic Energies and Dynamics in a CdS Quantum Dot through Reversible Protonation of Its Ligands.

This paper describes the pH dependence of the excitonic energies and dynamics of CdS quantum dots (QDs) capped with phosphonopropionate (PPA) in water. QDs capped with PPA carry a negative charge on their surfaces upon deprotonation of PPA above pH ∼ 8.5; the resultant electric field induces large changes in the QD's optical properties. Between pH 5.6 and 12.0, an increase in pH is accompanied by a 47-meV bathochromic shift in the bandgap of the QDs and a decrease in the Stokes shift by ∼4.3 meV/pH unit. An increase in the radiative recombination rate by a factor of 20.9 occurs on increasing the pH from 5.6 to 9.4. These observations are attributed to a shifting of the energy levels within the first exciton manifold, and are simulated using time-dependent density functional theory calculations on model Cd29S29 clusters surrounded by point charges.

Organic-to-Aqueous Phase Transfer of Cadmium Chalcogenide Quantum Dots using a Sulfur-Free Ligand for Enhanced Photoluminescence and Oxidative Stability.

This paper describes a procedure for transferring colloidal CdS and CdSe quantum dots (QDs) from organic solvents to water by exchanging their native hydrophobic ligands for phosphonopropionic acid (PPA) ligands, which bind to the QD surface through the phosphonate group. This method, which uses dimethylformamide as an intermediate transfer solvent, was developed in order to produce high-quality water soluble QDs with neither a sulfur-containing ligand nor a polymer encapsulation layer, both of which have disadvantages in applications of QDs to photocatalysis and biological imaging. CdS (CdSe) QDs were transferred to water with a 43% (48%) yield using PPA. The photoluminescence (PL) quantum yield for PPA-capped CdSe QDs is larger than that for QDs capped with the analogous sulfur-containing ligand, mercaptopropionic acid (MPA), by a factor of four at pH 7, and by up to a factor of 100 under basic conditions. The MPA ligands within MPA-capped QDs oxidize at Eox ~ +1.7 V vs. SCE, whereas cyclic voltammograms of PPA-capped QDs show no discerible oxidation peaks at applied potentials up to +2.5 V vs. SCE. The PPA-capped QDs are chemically and colloidally stable for at least five days in the dark, even in the presence of O2, and are stable when continuously illuminated for five days, when oxygen is excluded and a sacrificial reductant is present to capture photogenerated holes.

Early Detection, Referral, Investigation, and Diagnosis of Children with Growth Disorders.

Early diagnosis is a key objective in clinical medicine, and early detection of pathological short stature has tangible benefits for growth prognosis and the well-being of the child. Despite late diagnosis being common in growth disorders, programmes of height screening in primary care are not universal in developed countries and may be random or non-existent. A notable exception is automated growth monitoring in Finland, where an algorithm to detect abnormal growth is integrated into children's electronic health records, resulting in increased diagnoses of pathological short stature. Evidence-based anthropometric criteria for referral of short stature to secondary or tertiary care are now published, due largely to excellent studies in the Netherlands. Following referral of the short child, the protocol for laboratory investigations remains somewhat controversial because in healthy children their diagnostic yield can be too low for cost-effectiveness. However, outside of tertiary academic paediatric endocrinology centres, baseline screening tests are considered worthwhile and may speed up diagnosis and treatment. Finally, auxological cut-offs cannot replace good clinical practice, and the understanding that early and effective management depends on commitment to a diagnosis and individualisation of therapy in the short child cannot be overemphasised.

Escala breve de valoración psiquiátrica para niños (BPRS-C). Uso en diabetes insulinodependiente / Brief psychiatric rating scale for children (BPRS-C). Use in insulin dependent diabetes mellitus (IDDM) patients

El presente estudio es un escrutinio clínico, prospectivo, descriptivo y transversal, cuyo objetivo fue detectar picopatología en escolares con diagnóstico de diabetes mellitus insulinodependiente (DMID), así como la presencia de los padecimientos psicopatológicos más frecuentes. Se estudiaron 32 escolares, entre siete y 12 años de edad, con diagnóstico de DMID, con un mínimo de seis meses de evolución, tratados en el servicio de consulta externa de endocrinología del INP. El instrumento aplicado fue el BPRS-C (brief Psychiatric Rating Sacle for Children), escala de valoración psiquiátrica de 21 preguntas a los padres de los pacientes, a fin de detectar psicopatología. En 90.6 por ciento se encontró al menos un inciso sugestivo de enfermedad. En primer lugar están los problemas de conducta, seguidos por síntomas de hiperactividad y ansiedad, y en tercer lugar retraimiento y evitación social. No hubo elementos diagnósticos de procesos psicóticos, trastorno depresivo mayor, del pensamiento, o profundo del desarrollo