Quantum Dots or Qdot nanocrystals in principle have similar fluorescent properties to the traditional organic based fluorescent dyes commonly in use today. Fluorescence generated from previous known sources arises after excitation with a light source resulting in an electronic transition or emission of light (fluorescence) at a higher wavelength than the excitation source.
Unlike most fluorochromes that have skewed emission profiles with longer tails at the higher wavelength and thus overlap with other fluorochromes, Qdots have an almost normal distribution of fluorescence and hence require less electronic compensation between the various Qdots. The instruments available at the ICMS core facility allow some of the Qdots to be used in flow cytometry. The performance of short-wavelength infrared (SWIR) cameras in the visible and ultraviolet (UV) regions is limited by the absorption of high-energy photons in inactive regions of the imaging array.
Shibboleth is an access management service that provides single sign-on to protected resources. The Pietro research group is involved in the design, synthesis, and study of new electronic and electrooptical materials. Design and synthesis of novel molecular electronic conductors including transition metal containing electroactive and electrooptical polymeric materials. Recently a great deal of attention has been directed towards studying the properties of a new class of materials formed from conventional semiconductors. Semiconductor nanoclusters are envisioned as potential elements in novel electronic devices. Another research area focuses on the creation of new polycrystalline or polymeric materials with device activity. We have recently created a primative molecular diode based entirely on a class of molecular semiconductors known as metallophthalocyanines, (MPc).
Square planar metallophthalocyanines are capable of coordinating Lewis bases at the axial sites.
Some materials exhibit the property of electroluminescence, the emission of light when subjected to an applied voltage.
Our most recent research involves the use of silicate sol-gels as an encapsulating medium for electroactive and electroluminescent centers. Recently, semiconductor quantum dots (QDs) have been established as a valuable tool for labeling and sensing [1-3].
Even though the capillary electrophoresis (CE) is an extremely valuable separation analytical method and in combination with laser-induced fluorescence detection provides exceptionally low limits of detection, its application to analysis of fluorescent carbon nanomaterials is relatively limited [11]. In this work, preparation of CQDs from various precursors such as citric acid, sucrose and multiwall carbon nanotubes were synthetized, optically characterized by fluorescence spectrometry and investigated by capillary electrophoresis with laser-induced fluorescence detection. Qdots are the size of proteins (up to a few thousand molecules) at 10-20nm diameter and are made up of a semiconductor core, (cadmium with selenium or tellurium) and a shell of zinc sulphide that improves the optical properties of the qdot. Qdots generate their fluorescence in different manner in that the core and shell form excitons, which is analogous to the excited state of a fluorophore. These include Qdot 525, 585, 605, 655, 705, 800 the number refers to the emission peak of the Qdot.
Dual-band UV-SWIR imaging can be achieved by using PbS colloidal quantum dots (CQD) to downshift incident UV light to the SWIR band. It replaces the multiple user names and passwords necessary to access subscription-based content with a single user name and password that can be entered once per session. These materials show unusual quantum confinement effects and electronic interactions with the surface functionalities.
Our sol-gels are silicate networks incorporating electroactive and electrooptical centers such as phophorescent ruthenium polypyridyls, redox-active phthalocyanines, and electroluminescent transition metal complexes.
These materials, called quantum confined nanoclusters or quantum dots, are tiny spheres (ca. However, one question that needs to be addressed concerns the electronic contact between the surface groups and the semiconductor core. Metallophthalocyanines are coordination compounds in which a central transition metal is coordinated to a large, planar macrocyclic tetradentate ligand known as phthalocyanine. Thus, semiconducting films of various M(Pc)s can act as redox catalysts on the surface of an electrode.
Electroluminscence differs from incandescence, which is the black-body radiation emitted from a heated object (like in a conventional light bulb), fluorescence, which is the light emitted from some materials when stimulated by a higher energy light source (like in a fluorescent lamp), and cathodoluminescence - emission due to high energy electron bombardment, as in a television or computer screen (unless you have a LCD display, the light you're looking at right now is cathodoluminescence). Sol-gels are solid matrices formed by crosslinking colloidal particles, and are actually quite common in our everyday lives.
However, semiconductor quantum dots possess certain limitations such as high toxicity due to the use of heavy metals in their production. In contrast to stationary fluorescence spectrometry, CE is capable to reveal the presence of various species in the sample due to their different electrophoretic mobility. Fluorescent carbon nanoparticles: Electrochemical synthesis and their ph sensitive photoluminescence properties. A carbon nanoparticle-based low-background biosensing platform for sensitive and label-free fluorescent assay of DNA methylation. Easy synthesis and imaging applications of cross-linked green fluorescent hollow carbon nanoparticles. These excitons have a much longer lifetime than normally generated fluorescence, the by-product of which makes the Qdot virtually non-photo bleachable and hence is ideal for detecting low density antigens.
All Qdots are maximally excited by short wavelength lasers such as UV or Violet diodes (405nm) and so any three can used on the FACS Aria. The CQD downshifting layer has minimal impact on the SWIR imaging performance and greatly increases the UV sensitivity of an InGaAs camera.
Our research has thus far resulted in the creation of a variety of new materials and molecular devices, such as a ruthenium polypyridyl based electroluminescent film-castable polymer, an electroluminescent gel, a phthalocyanine based molecular diode, and a thiol detecting film. During precipitation, a competition occurs between sulfide and thiolate (formed from the sulfide induced deprotonation of the thiol) to condense with the cadmium cation.
We qualitatively measured the degree of electronic communication by covalently attaching a fluorescent probe to a CdS nanocluster bearing electron withdrawing or donating surface groups, and observing the emission intensity as a function of the surface electron demand. In crystalline films of metallophthalocyanines the rings stack on top of one another creating bands of p-orbitals capable of delocalizing electron density throughout the entire film.

We found that tetraaminophthalocyaninatocobalt(II), (TAPc)Co, shown to the left, acts as an effective electrocatalyst for the reduction of N2O to N2 on the surface of graphite electrodes. Electroluminescent panels are commercially available, and offer many advantages over LED, incandescent, fluorescent, or cathodoluminescent light sources. Nulla consectetur, dolor ut tincidunt tempor, metus justo sagittis libero, id molestie lectus justo in purus. It is known that heavy metals are highly toxic even at relatively low levels, which may prove prohibitive to any clinical studies.
The size of the Qdot is proportional to the energy of the excitons within it, the larger the Qdot the longer the wavelength of the fluorescence emitted.
A dual-lens design in which the QDs are incorporated on a removable substrate is demonstrated, which provides UV sensitivity without modification of the InGaAs camera focal plane array.
If your institution uses Shibboleth authentication, please contact your site administrator to receive your user name and password. Such new materials are not only scientifically very exciting, but hold the promise of revolutionary impact on the future of the electronics industry. The differences arise primarily from quantum confinement effects, the reduction of band structure into discrete quantum levels resulting from the limited size of the particle. The probe is a tris-bipyridyl ruthenium complex with a substitution on one of the ligands to allow for covalent attachment to the quantum dot. The simple diode, a component which allows current to pass through it only in one direction, is an example of an electronic device.
The cobalt center coordinates the N2O molecule while the electron rich pi system of the Pc ring facilitates electron transfer.
They can be made large or small, they are flat and thin, the light can be rapidly modulated, and they are available in a few different colors. This prompted the creation of carbon-based fluorescent nanoparticles (CQDs) to replace semiconductor QDs due to their low toxicity, biocompatibility, low cost and chemical inertness in addition to having similar fluorescence properties [4].
A single-lens design in which the QDs are deposited directly on the focal plane array is demonstrated using both a standard InGaAs focal plane and a substrate-thinned focal plane.
Quantum confinement effects in semiconductor nanoclusters may lead to heretofore unheard-of electronic devices such as single electron transistors and UV light emitting diodes. Eventually, the thiolates completely encapsulate the CdS cluster and arrest further growth of the nanocrystal. Although quite elementary in its function and construction, the diode is easily the most important single device in today's electronics industry. We discovered that junctions between thin films of two differently substituted metallophthalocyanine rings, Cu(PcF8) and Ni(Pc), act as diode junctions, allowing current to pass preferentially in one direction. M(Pc) films are particularaly attractive as electrocatalysts because the energy of the pi system is greatly affected by peripheral substituents. These properties make electroluminescent panels ideal candidates for heads-up displays, front panel displays for electronic equipment (the Timex Indiglo watch uses an electroluminescent panel), and flat-screen TV. Jaworski"Dual-band ultraviolet-short-wavelength infrared imaging via luminescent downshifting with colloidal quantum dots", J. Our research in this area has focused on (1) the chemical functionalization of the surface of the nanocluster spheres, and (2) determining the chemical activity of the surface funtionalitites. By adjusting the mole ratio of sulfide to thiolate, one can control the size of the nanocluster. To control the degree of surface electron demand, we substituted a corresponding fraction of the thiophenolate capping groups with p-nitrothiophenolate.
Almost all other semiconductor devices, from transistors to complex microprocessor chips, are created primarily from diode junctions. We are continuing to explore the basic properties of diode junctions formed between a variety of metallophthalocyanine based molecular semiconductors and conventional semiconductor films. The presence of the four amino groups on the ring renders the pi system electron rich, and results in a strong reduction catalyst. Thus far, we have successfully created a number of surface functionalized CdS quantum dots, and demonstrated that the functionalities can be used to covalently anchor interesting moieties, such as dyes, electroactive molecules, luminophores, and transition metal complexes, onto the nanocluster surface. We obsered that the probe emission was rapidly quenched as the mole percentage of nitro on the surface increased, falling to under 20% of the original intensity with only 20% mole fraction nitro. At present virtually all diode junctions used in electronics are fabricated from single crystals or crystalline films of conventional semiconductors such as doped silicon or germanium.
Consequently, by making the pi system electron deficient, we created a powerful oxidation catalyst. The electronically excited dopant atom is the actual light source; the purpose of the semiconductor is to provide a matrix for the electrons to move freely. The sol is then kept at slightly elevated temperature for several days, during which time the linear chains crosslink to form the gel. Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos himenaeos.
We have even demonstrated that surface functionalities can be used to polymerize quantum dots. Once attached, the surface groups are chemically active and can be used as an anchor to tether a variety of electron withdrawing, electron donating, redox active, or optically interesting moieties.
However, within the past two decades an exciting new class of semiconductor materials have been discovered. Thus, we found that semiconducting films of the cobalt phthalocyanine derivative, (Tmtppa)Co, shown to the right, catalyse the oxidation of hydrazine and hydroxylamine to N2. The gel is actually a three-dimensional solid matrix encapsulating voids filled with aqueous methanol.
We have also demonstrated that the surface functionalities are in facile electronic communication with the semiconductor core, and the surface groups are even in direct electronic communication with each other through the core. CdS quantum confined nanoclusters are, however, quite sensitive to harsh reaction conditions. Unlike conventional atomic semiconductors, molecular semiconductors are based on organic, inorganic, or metal-organic molecular solids or polymers.

As with the (TAPc)Co, (Tmtppa)Co first coordinates the ligand, but in this case holes are transfered from the electrode oxidizing the coordinated amine. We have recently discovered that the transition metal moiety bisbipyridinechlororuthenium (III), illustrated above left, coordinated to a semiconductive polymer can be placed directly into an excited state by electron capture from the polymer's conduction band. Thus, our group has worked out a number of methodologies for carrying out surface reactions under such conditions as to not disrupt the integrety of the nanocluster. These data demonstrate facile electronic communication between the semiconductor core and the thethered surface groups, as well as between remote surface sites mediated by the core. And, unlike atomic semiconductors, the electronic and physical properties of molecular semiconductors can be vastly altered by modification of their molecular structures. Relaxation of the excited state occurs with light emission and subsequent hole capture from the polymer's valence band. The gel then enters the drying phase where the aqueous methanol evaporates promoting further crosslinking and causing the gel to physically shrink. Maecenas ullamcorper, augue ut tempor lacinia, lectus purus interdum velit, ut ultricies ipsum velit id felis.
We hope that our research in this area may lead to a better understanding of the electronic relationships between the nanocluster core and surface structures, and perhaps lead to the creation of new and unusual electronic devices. One such method involves the reaction of a phenolic surface quantum dot with an N-acylimidazole.
Further evidence of facile surface-core electronic communication can be deduced from the relative decomposition rates of surface functionallized nanoclusters.
One goal of research in this area is to someday enable chemists to tailor-make semiconducting materials with prespecified electronic properties, and create molecular devices with highly specific electronic functions.
By monitoring the open cell potential of an M(Pc) modified graphite electrode, one can detect the presence of trace amounts of target compound.
Light emission continues under the influence of an electric field sourcing electrons to the conduction band and holes to the valence band.
At temperatures below about 100 degrees the shrinking process will continue until about 25% of the original volume of aqueous methanol remains in the voids and the gel appears as a transparent solid glassy material.
With this method a wide variety of groups can be tethered to the surface of the nanocluster. We observed that strongly electron withdrawing or donating surfaces promote UV photodecomposition of the nanocluster, whereas surfaces that are relatively neutral in electron demand give rise to photostable nanoclusters. We have thus far created M(Pc) based sensors for O2, CO, CO2, NO, N2O, NO2, and S2-, and are currently researching the possibility of creating highly sensitive and highly selective M(Pc) based thiol sensors for detecting the metabolites of bacteria. Our continuing research in this area is directed towards the synthesis and study of novel transition metal containing electroluminophores coordinated to a variety of different semiconductive polymers. Importantly, any solute dissolved in the aqueous phase will be entrapped in the voids, while any hydrophobic solutes will intercalate in the sol-gel matrix itself. We also observed that the only products produced in the photodecomposition were CdS(s) and the disulfide corresponding to the capping thiolate.
Although scientifically interesting, this material is not useful in a practical device due to low quantum yield. Hence, silicate sol-gels are ideal candidates for the creation of novel electrooptical materials.
For example, the IR spectrum of the decanoyl esterified phenolic quantum dot is shown below.
Thus, we proposed a mechanism for the photodecomposition of surface functionalized CdS nanoclusters, as shown below.
They are transparent, ionically conductive, and capable of immobilizing hydrophilic and hydrophobic species in separate compartments. The IR spectrum clearly shows vibrational bands arising from the aromatic and aliphatic sections of the capping groups.
This mechanism involves the separation of the photoinduced exciton by band bending at the surface. In an effort to increase hole conductivity to the ruthenium center, we created a series of alternating block copolymers, as shown on the right.
Two important features to note in the IR spectrum are the presence of the strong ester carbonyl stretching vibration, and the almost complete absence of a phenolic hydroxyl band, indicating near quantitative esterification of the surface groups.
In the aniline surface example below, the hole floats to the surface of the nanocluster, while the electron sinks to the core where it is trapped. The block in green is the emissive center, while the block in red enhances hole mobility through the polymer chain. Our preliminary studies have shown all of our polypyridyl containing polymers to be electroluminescent. Not only are the proton resonances fully assignable, but they appear considerably broadened, due to the hindered tumbling rate of the large nanocluster on the NMR timescale. Our research on surface functionalized quantum confined semiconductor nanoclusters has thus far demonstrated facile surface-core electronic communication and core-mediated electronic communication between remote surface groups. We are now in the process of quantifying the electroluminescent behavior of these novel and interesting systems.
This is further evidence that the functionalization group is covalently bound to the surface and not in dynamic equilibrium with solution phase species. Our future investigations will focus on the application of these concepts to the fabrication of novel electronic devices using quantum confined nanoclusters. Note the homogeneously broadened proton resonances of the surface bound groups as compared to the sharp resonances of the solvent residuals (marked with *).

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