Search

This paper describes a new system for non-electronic communication that can transmit alphanumeric information encoded as pulses of light, over intervals of hours. The objective of this research was to design “infofuses” that improved the previously described systems in three ways: 1) they could transmit information for hours instead of seconds, 2) they could transmit long messages, and 3) they resisted accidental extinction. These characteristics improve the functionality and potential for practical use of infofuses, and make themmore convenient to use as a test bed for a new approach to fusing chemistry and information—“infochemistry”. We consider the elements of a system for manipulating information that comprises seven steps: 1) generating the message (either by writing it, or by collecting it from a sensor), 2) encoding the information in a form that a device can transmit, 3) transmitting the information, 4) receiving the information, 5) decoding the information, 6) interpreting the decoded information, 7) acting on this information. Here, we focus on steps (2) and (3). To simplify the problem, we assume that reception and decoding will be accomplished optically and electronically, and that there are no constraints (that we must consider) on the complexity, cost, or performance of the systems that accomplish these functions. We also assume that generating the message involves a separate set of issues which may or may not be primarily chemical. Systems based on infochemistry combine the storage and transmission of encoded information with four attractive features of chemistry: 1) high energy density; 2) autonomous generation of power that can be used for both sensing and for transmission; 3) no requirement for batteries; 4) facile coupling with certain kinds of chemical sensing. We have described two infochemical systems that do not require external electrical power (they use only chemical interactions or reactions) to transmit alphanumeric information. The first system—which we call an “infofuse”—is based on a strip of flammable polymer (nitrocellulose). In this system, patterns of spots of thermally emissive salts encode information. The second—which we call a “droplet shutter”—is a microfluidic device that capitalizes on the high stability of operation of a flow-focusing nozzle to generate bubbles and droplets. In this system, windows in an opaque mask encode information. The combination of optically transparent droplets and windows serve as optical shutters. A third system—a frequency-agile microdroplet-based laser—requires electrical power to operate the pump laser, and is intended for different applications. In our previous design of infofuses, information was encoded as patterns of ions (Li, Rb, Cs) on a strip of nitrocellulose. Ignition of one end of a nitrocellulose strip initiated propagation of a flame-front (at T 1000 8C) at 2– 3 cms . As this moving hot zone reached each spot containing added metal ions, it caused the emission of light at wavelengths characteristic of the thermal emission of the corresponding atomic species. The pattern of emissive salts, ordered in space, therefore, became a sequence of pulses of light at characteristic wavelengths, ordered in time. We have described infofuses that used three thermal emitters (the perchlorate or nitrate salts of Li, Rb, and Cs, with Na as an internal standard for intensity) to encode and transmit alphanumeric messages. Because each of these three ions can either be present or absent in a particular spot, there are seven unique combinations (2 1; we have chosen not to use 0,0,0 to avoid ambiguities between a pulse and a space between pulses). Seven unique pulses allow an encoding scheme that assigned alphanumeric characters to combinations of two (7= 49) sequential optical pulses. The infofuses fabricated according to this design demonstrated the principle of a successful strategy for coupling chemistry with the encoding and transmitting of chemical information, but suffered from a number of weaknesses. Two were of primary concern to us: 1) While burning, the flame-front had to remain far (> 1– 2 mm) from surfaces, so that the heat transfer from the flame to the surface did not cool and extinguish the flame. When the flame-front of nitrocellulose infofuses with dimensions we used (1–3 mm wide, ca. 100 mm thick) came close (< 1–2 mm) to any solid surface, their rate of propagation decreased, and the flame frequently extinguished. This characteristic required that the burning infofuses have a vertical orientation, and be out of contact with solid surfaces; these restrictions limited the practical applicability of these infofuses. 2) The rapid propagation of the flame-front (ca. 3 cms ) precluded times of transmission longer than about 1 min (an infofuse on which the flame propagated at this rate would require a length of 2.6 km to transmit continuous or repetitive messages for 24 h). Here we describe a new experimental platform for infofuses that addresses these weaknesses by using a “dualspeed” arrangement (Figure 1), in which a fuse that burns slowly and continuously (a “SlowFuse”) and that does not transmit information, intermittently ignites fuses (strips of nitrocellulose) that burn quickly and transmit information [*] Dr. C. Kim, Dr. S. W. Thomas, III, Prof. G. M. Whitesides Department of Chemistry and Chemical Biology Harvard University 12 Oxford Street, Cambridge, MA 02138 (USA) E-mail: gwhitesides@gmwgroup.harvard.edu

This article describes a new procedure for generating and transmitting a message--a sequence of optical pulses--by aligning a mask (an opaque sheet containing transparent "windows") below a microfluidic channel in which flows an opaque continuous fluid containing transparent droplets. The optical mask encodes the message as a unique sequence of windows that can transmit or block light; the flow of transparent droplets in the channel converts this message into a sequence of optical pulses. The properties of the windows on the mask (e.g., their size, wavelength of transmittance, orientation of polarization) determine the information carried in these optical pulses (e.g., intensity, color, polarization). The structure of a transmitted signal depends on the number and spacing of droplets in the channel. Fourier transformation can deconvolve superimposed signals created by the flow of multiple droplets into the message that a single droplet would transmit. The research described in this contribution explores a new field at the intersection of chemistry, materials science, and information technology: infochemistry.

This paper describes a method for the purification of monoclonal antibodies (rat anti-2,4-dinitrophenyl IgG: IgG(DNP); and mouse antidigoxin IgG: IgG(Dgn)) from ascites fluid. This procedure (for IgG(DNP)) has three steps: (i) precipitation of proteins heavier than immunoglobulins with ammonium sulfate; (ii) formation of cyclic complexes of IgG(DNP) by causing it to bind to synthetic multivalent haptens containing multiple DNP groups; (iii) selective precipitation of these dimers, trimers, and higher oligomers of the target antibody, followed by regeneration of the free antibody. This procedure separates the targeted antibody from a mixture of antibodies, as well as from other proteins and globulins in a biological fluid. This method is applicable to antibodies with a wide range of monovalent binding constants (0.1 microM to 0.1 nM). The multivalent ligands we used (derivatives of DNP and digoxin) isolated IgG(DNP) and IgG(Dgn) from ascites fluid in yields of >80% and with >95% purity. This technique has two advantages over conventional chromatographic methods for purifying antibodies: (i) it is selective for antibodies with two active Fab binding sites (both sites are required to form the cyclic complexes) over antibodies with one or zero active Fab binding sites; (ii) it does not require chromatographic separation. It has the disadvantage that the structure of the hapten must be compatible with the synthesis of bi- and/or trivalent analogues.

This article describes a prototype system for quantifying bioassays, and for exchanging the results of the assays digitally with physicians located off-site. The system uses paper-based microfluidic devices for running multiple assays simultaneously, camera phones or portable scanners for digitizing the intensity of color associated with each colorimetric assay, and established communications infrastructure for transferring the digital information from the assay site to an off-site laboratory for analysis by a trained medical professional; the diagnosis then can be returned directly to the healthcare provider in the field. The microfluidic devices were fabricated in paper using photolithography, and were functionalized with reagents for colorimetric assays. The results of the assays were quantified by comparing the intensities of the color developed in each assay with those of calibration curves. An example of this system quantified clinically relevant concentrations of glucose and protein in artificial urine. The combination of patterned paper, a portable method for obtaining digital images, and a method for exchanging results of the assays with off-site diagnosticians offers new opportunities for inexpensive monitoring of health, especially in situations that require physicians to travel to patients (e.g., in the developing world, in emergency management, and during field operations by the military) to obtain diagnostic information that might be obtained more effectively by less valuable personnel.

Surface-bound molecular rotation can occur with the rotational axis either perpendicular (azimuthal) or parallel (altitudinal) to the surface. The majority of molecular rotor studies involve azimuthal rotors, whereas very few altitudinal rotors have been reported. In this work, altitudinal rotors are formed by means of coupling aryl halides through a surface-mediated Ullmann coupling reaction, producing a reaction state-dependent altitudinal molecular rotor/stator. All steps in the reaction on a Cu(111) surface are visualized by low-temperature scanning tunneling microscopy. The intermediate stage of the coupling reaction is a metal-organic complex consisting of two aryl groups attached to a single copper atom with the aryl rings angled away from the surface. This conformation leads to nearly unhindered rotational motion of ethyl groups at the para positions of the aryl rings. Rotational events of the ethyl group are both induced and quantified by electron tunneling current versus time measurements and are only observed for the intermediate structure of the Ullmann coupling reaction, not the starting material or finished product in which the ethyl groups are static. We perform an extensive set of inelastic electron tunneling driven rotation experiments that reveal that torsional motion around the ethyl group is stimulated by tunneling electrons in a one-electron process with an excitation energy threshold of 45 meV. This chemically tunable system offers an ideal platform for examining many fundamental aspects of the dynamics of chemically tunable molecular rotor and motors.

This paper describes the influence of steric and electronic factors in the regioselectivity of endoperoxide formation of tetracene derivatives using (1)O2. A combination of kinetics experiments and product distributions resulting from these photosensitized oxidations demonstrates that, while the steric effect of o-alkyl groups on aryl substituents is highly localized to the substituted ring, the resistance to oxidation based on phenylethynyl substituents is more evenly distributed between the two reactive rings. These results are important for the rational design of highly persistent acenes.

Free-standing, stimuli-responsive polyelectrolyte multilayer films enabled by light-induced degradation of sacrificial compartments are introduced. Two examples are described: i) a triple responsive film that uses light, redox, and pH for different functions, and ii) different wavelengths of light for different functions. This approach to multiresponsive materials offers simple design and chemical synthesis while enabling different stimuli to perform separate functions in the same material.

Hydrazine, a heavily used industrial chemical, has been implicated as a carcinogen and is readily absorbed through the skin. Its strong reducing power has led to its use as an oxygen scavenger and corrosion inhibitor in various applications involving water-heating systems, as well as a fuel in rocketpropulsion systems. As a result of its toxicity and reactivity, facile detection of hydrazine is also relevant to homeland security. Traditional analytical methods utilized for hydrazine detection include spectrophotometric detection, as well as assorted electrochemical schemes. The expansion of conjugated polymer sensory materials has also led to their application towards the detection of hydrazine. Of primary interest have been the conducting properties of polypyrrole, polythiophene, and polyaniline. To our knowledge, however, amplifying fluorescent polymers (AFPs) have not been explored for hydrazine detection. AFPs show very high sensitivities to quenching analytes such as 2,4,6trinitrotoluene (TNT) via a photoinduced electron-transfer quenching (“turn-off”) mechanism. This sensitivity of fluorescence quenching is due to a combination of interand intrachain exciton transport in thin films. Herein we report a “turn-on” fluorescence detection method for hydrazine vapor with AFPs. We investigated several polymers (P1–P3) for hydrazine detection. These conjugated polymers are structurally related poly(phenylene ethynylene)s (PPEs), varying in their degree of electron density along the polymer chain. The response of P3 to saturated hydrazine vapor (10 s exposure) is given in Figure 1. It is clear from Figure 1 that no new emitting species were generated by exposure to hydrazine since the spectral shape does not change. In addition, the excitation spectrum of the polymer remained the same after the introduction of hydrazine. The other conjugated polymers investigated also showed no change in the shape of their emission spectra upon exposure to hydrazine vapor (see Supporting Information).

A self-polymerizable AB-type monomer for Diels−Alder (D−A) polymerization was prepared, and its polymerization was carried out in the melt phase and at high pressure in solution. The former method generated only low-molecular-weight polymer, but the latter one offered an efficient polymerization with increased molecular weight, due to the effect of high pressure on reactions with a negative activation volume. A pyridinium p-toluenesulfonate-catalyzed dehydration reaction of the D−A polymer led to a novel aromatic ladder polymer, poly(iptycene), which is soluble in common organic solvents and stable up to 350 °C. The NMR and UV−vis spectra of these polymers match the spectra of their corresponding model compounds, the synthesis of which is also reported.

Conjugated polymers (CPs) containing amino groups have been synthesized, and their optical properties in both solution and thin film have been studied. New monomers required for the synthesis of these polymers have been readily prepared via efficient synthetic routes. These monomers have been successfully polymerized with a variety of comonomers. The spectral positions of the absorption and emission spectra correlate with the degree of electron density on the polymer chain. Polymers containing N-alkylcarbazole units display similar optical properties in solution to most CPs. Polymers with dialkylamino groups, however, display very different optical properties, including broadened absorbance and emission spectra, larger Stokes shifts, and longer excited state lifetimes. These results are consistent with a significant difference between the molecular geometries of the absorbing and emitting states. The solid state emission of most of the polymers is sufficient to warrant them for consideration as fluorescent sensing materials.

This paper describes the photochemical tuning of net charge that develops from contact electrification. The net charge separation and/or rate of charging of photochromic spiropyran (SP)-containing polymer films can be controlled by irradiation with UV light. The isomerization of the SP form to the more hydrophilic merocyanine (MC) by irradiation with UV light always leads to films that charge more positively than before irradiation. The incorporation of a halogenated comonomer into ring-opening metathesis polymerization (ROMP) yields films that charged negatively before irradiation so that a change in sign of the net charge separation of the film could be observed upon irradiation. An important advantage to our photochromic system is that light can be used to tune the charging behavior of the material, with spatial or temporal control of irradiation, leading to films that resist charging. Furthermore, the observed trends can be reversed by the exposure of the SP-containing polymer films to heat or visible light.

This communication describes photoresponsive gels, prepared using ring-opening metathesis polymerization (ROMP), that dissolve upon irradiation with ultraviolet light. Exposure of mixtures of norbornene-type ROMP monomers and new photoreactive cross-linkers comprising two norbornene units bound through a chain containing o-nitrobenzyl esters (NBEs) to well-known ruthenium carbene catalysts gave cross-linked polymer networks that swelled in organic solvents or water depending on the structure of the monomer. These gels became homogeneous upon irradiation with UV light, consistent with breaking of the cross-links through photolysis of the NBE groups. The irradiation time required for homogenization of the gels depended on the cross-link density and the structure of the photoresponsive cross-linker.

This paper describes thin films comprising acenes dispersed in a conjugated polymeric host that have a ratiometric photoluminescence response to singlet oxygen. These films also respond to irradiation of protein-bound sensitizers, which represents a solution to the problem of protein–conjugated polymer non-specific interactions.

Photoreactive polyelectrolyte multilayers (PEMs) that dissolve upon UV irradiation are described. Light-induced switching of the formal charge of a photoreactive polycation resulted in repulsive interlayer electrostatic forces, and caused the dissolution of PEM films. Combining both photoreactive and inert polycations in the same film yielded additional control over the light-induced change in film thickness.

This communication describes new conjugated polymers that bear diarylanthracene or diaryltetracene pendants and respond to singlet oxygen by interrupting energy transfer resulting in blue-shifted fluorescence.

This article describes a self-powered system that uses chemical reactions—the thermal excitation of alkali metals—to transmit coded alphanumeric information. The transmitter (an “infofuse”) is a strip of the flammable polymer nitrocellulose patterned with alkali metal ions; this pattern encodes the information. The wavelengths of 2 consecutive pulses of light represent each alphanumeric character. While burning, infofuses transmit a sequence of pulses (at 5–20 Hz) of atomic emission that correspond to the sequence of metallic salts (and therefore to the encoded information). This system combines information technology and chemical reactions into a new area—“infochemistry”—that is the first step toward systems that combine sensing and transduction of chemical signals with multicolor transmission of alphanumeric information.

This paper describes the phase separation of millimetre-scale spheres based on electrostatic charge. Initially, polymeric (Teflon, T; Nylon-6,6, N) and metallic (gold-coated Nylon-6,6, Au(N)) spheres are uniformly mixed in a two-dimensional (2D) monolayer on a gold-coated plate. Oscillating the plate vertically caused the spheres to charge by contact electrification (tribocharging). Positively charged N and negatively charged T spheres attracted each other more strongly than they attracted the capacitively charged, Au(N) spheres. The T and N spheres formed 2D Coulombic crystals, and these crystals separated from the Au(N) spheres. The extent and rate of separation increased with increasing amplitude of agitation during tribocharging, and with decreasing density of spheres on the surface. At high surface density, the T and N spheres did not separate from the Au(N) spheres. This system models the 2D nucleation of an ionic crystal from a polarizable liquid.

Publisher Summary This chapter focuses on the use of amplified fluorescent polymers in the detection of explosives. Chemical sensing using fluorescent quenching (FQ) of amplified fluorescent conjugated polymers is a powerful technique that can achieve high sensitivity for vapor-phase analytes. Electron-transfer-induced FQ is the most practical and efficient mechanism of signal transduction for the detection of explosives, such as 2,4,6-trinitrotoluene (TNT), as they are often highly electron-deficient molecules that readily accept electrons from excited fluorophores. Explosive devices that contain TNT also usually contain a synthetic by-product called 2,4-dinitrotoluene (DNT), which is also highly electron deficient. Several different types of operable devices have been successfully fabricated by ICx Technologies under the name Fido, which allows the use of a small amount of associated optics and electronics. As a result, complete, portable hand-held devices weighing less than 2 lb have been developed and successfully tested for personnel, vehicle, and container screening. The ability of this technology to support small, lightweight, and portable devices has in part led it to be especially successful in the detection of land mines, where the principal explosive component is TNT. These sensor devices respond only to nitroaromatics and similarly small, electron-deficient analytes, which are found typically only in or close to explosives and explosive devices. As a result, this technology has been successfully field tested in many different scenarios, from the screening of vehicles to the detection of land mines and even underwater explosive detection. The effectiveness and applicability of these materials and devices are constantly being improved by research in both industry and academia.

This presentation describes the mechanistic investigations and applications of space-charge electrets fabricated by contact electrification. The electrostatic self-assembly of oppositely-charged electrets is also investigated, which can self-assemble in two and three dimensions.

Heavy metal complexes that are phosphorescent at room temperature are becoming increasingly important in materials chemistry, principally due to their use in phosphorescent organic light-emitting devices (OLEDs). Their use in optical sensory schemes, however, has not been heavily explored. Homoleptic bis-cyclometalated Pt(II) complexes are known to undergo oxidative addition with appropriate electrophiles (principally alkyl halides) by either thermal or photochemical activation. We have applied this general reaction scheme to the development of a phosphorescence-based sensing system for cyanogen halides. To carry out structure-property relationship studies, a series of previously unreported Pt(II) complexes was prepared. Most of the complexes (excluding those that incorporated substituents on the ligands that forced steric crowding in the square plane) were strongly orange-red phosphorescent (Phi = 0.2-0.3) in a room-temperature oxygen-free solution. These sterically demanding ligands also accelerated the addition of cyanogen bromide to these complexes but slowed the addition of methyl iodide, indicating that the oxidative addition mechanisms for these two electrophiles is different. The lack of solvent-polarity effect on the addition of BrCN suggests a radical mechanism. Oxidative addition of BrCN to the metal complexes in solution or dispersed in poly(methyl methacrylate) gave blue-shifted emissive Pt(IV) complexes. The blue-shifted products give a dark-field sensing scheme that is in sharp contrast to energy transfer-based sensing schemes, which have limited signal-to-noise because of the presence of lower-energy vibronic bands of the energy donor that can overlap with the emission of the acceptor.

In this Letter, we report the confinement of a uniform beam of light (${\ensuremath{\lambda}}_{1}=400\text{ }\text{ }\mathrm{nm}$) at the nodes of a standing wave (${\ensuremath{\lambda}}_{2}=532\text{ }\text{ }\mathrm{nm}$) via absorbance modulation. In the present implementation of absorbance modulation, a thin polymer film containing a photochromic azobenzene side chain is exposed to a standing wave at ${\ensuremath{\lambda}}_{2}$ and a uniform beam at ${\ensuremath{\lambda}}_{1}$, resulting in alternate regions of high and low absorbance. Light at ${\ensuremath{\lambda}}_{1}$ is localized around the low-absorbance regions. Using photoresist exposures, we mapped out the localized light intensity distribution, which agrees well with our theoretical model. Since the width of this distribution is primarily determined by the ratio of the intensities at the two wavelengths, this technique opens up the possibility of localizing light fields below the diffraction limit using far-field optics.

Structural and electronic effects on the efficiency of DMNB detection with fluorescent conjugated polymers are described.

A new imaging system based on a photoinitiated electron transfer chain reaction is reported. Specifically, irradiation of 9,10-dicyanoanthracene (sensitizer) leads to the conversion of Dewar benzene derivatives (reactants) to benzene derivatives (products) within solid polymer films. The mechanism of the reaction may involve chemical amplification with cation radicals ("holes") as the catalytic species. We present herein studies of both molecularly doped polymers and polymers containing Dewar benzene moieties attached to side chains. The refractive index of the materials could be tuned within a narrow range using this photochemical reaction, as demonstrated by the writing of persistent gratings in forced Rayleigh scattering experiments.

This letter presents an integrated complementary metal-oxide semiconductor fluorometer that utilizes frequency-domain fluorescence lifetime imaging spectroscopy for oxygen-sensing applications. The implemented fluorometer chip consists of a p+/n-well/p-substrate photodiode, a phase readout circuit with integrated zero-crossing detection to extract the frequency-domain phase shift into a time-domain delay, and a high-resolution time-to-digital converter for digital quantization of the converted time delay. The fabricated fluorometer consumes less than 8.3 mW power and has a temporal resolution of 110 ps. During oxygen-sensing experiments, a ruthenium complex was used as an oxygen-sensitive dye whose lifetime was measured as a function of the of the oxygen concentration in water.

This communication describes a new approach for controlling static charging (contact electrification), and resulting electrical discharging, that occurs when two contacting materials separate. The prevention of contact electrification is an important problem; unwanted adhesion between oppositely charged materials, spark-initiated explosions, and damage to microelectronic circuitry are some of the deleterious effects of static charging. Current strategies for controlling contact electrification rely upon dissipating an accumulated charge by making contacting surfaces conductive and, therefore, can be difficult to implement with electrically insulating materials. Specifically, using our understanding of the ion-transfer mechanism of contact electrification, we patterned glass slides with negatively charging areas (clean glass) and positively charging areas (glass silanized with a cationic siloxane terminated with a quaternary ammonium group). The rate of charge separation due to a steel sphere rolling on the patterned glass surface correlated linearly with the percentage of the glass surface that was silanized; the rate of charge transfer was minimal when 50% of the glass surface area was silanized. Patterned surfaces also prevented electrical discharges between electrically conducting (bare steel) or insulating (acrylate-coated steel) spheres rolling on the glass, because the rate of charging was sufficiently slow to prevent electric fields greater than the dielectric strength of air to develop. This strategy for preventing static charging therefore does not require one of the two contacting surfaces to be electrically conductive. More generally, these results show that our enhanced understanding of the ion-transfer mechanism of contact electrification enables the rational design of chemically tailored surfaces for functional electrets.

We describe herein a polymeric material that prefers to align perpendicular to a stretch-aligned polymer host in the solid state. Poly(iptycene) poly-1 was synthesized from monomer 1 under hyperbaric techniques via a Diels-Alder polymerization. Polarized excitation spectra of the anthracene end groups in this material in a stretch-aligned, solution-cast poly(vinyl chloride) (PVC) film showed that the poly(iptycene) prefers to align normal (counter aspect ratio) to the stretching direction of the PVC. This is explained by a "threading" mechanism, whereby the PVC intercalates through the internal free volume presented by poly-1, similar to effects observed in small molecule iptycenes under similar conditions.

This paper describes a previously unreported class of sterically crowded tetracene derivatives that have both phenyl and ethynyl substituents. The steric crowding above and below the tetracene core prevents overlap between the extended π-systems of the acenes. Substituent effects cause these tetra-substituted tetracenes to have absorbance and fluorescence spectra red shifted from either disubstituted derivatives or rubrenes, such that they have spectra similar to diarylpentacenes, but with higher quantum yields of fluorescence and greater photostability. These new molecules also undergo cycloaddition reactions with 1O2, giving regioisomeric mixtures of endoperoxides, and in contrast to longer acenes, the ethynyl substituents show only a modest stabilizing effect to photooxidation. Ethynylated tetracenes also exhibited photochromism, with their endoperoxides undergoing cycloreversion to yield the acene starting material at room temperature in the dark.

This article describes photoactivatable conjugated oligomers that show both increased fluorescence quantum yield and pH-dependant solubility upon irradiation with UV light. Sonogashira coupling between ester-substituted phenylacetylenes and alkoxy-substituted diiodo phenylene-vinylenes yielded conjugated phenylene-ethynylene/phenylene-vinylene oligomers. Oligomers with nitrobenzyl ester moieties had quenched fluorescence in polar solvents; UV irradiation restored their quantum yield of fluorescence to that of corresponding alkyl ester-substituted oligomers. These photocaged oligomers also exhibited UV-induced changes in solubility consistent with photogeneration of carboxylic acids. This approach is therefore effective at tuning the properties of conjugated organics with light after traditional synthetic operations, and has potential for use in photoactivatable fluorophores or solution-processable multilayer devices.

We report the imaging of sub-diffraction limited features using an optical probe generated by focusing a round spot at one wavelength, lambda(1) = 405 nm, and a ring-shaped spot at a second wavelength, lambda(2) = 532 nm, onto a thin photochromic layer that coats the nanostructures. Illumination at lambda(2) turns the photochromic layer opaque to lambda(1) everywhere except at the centre of the ring, where the illumination at lambda(1) penetrates and probes the underlying nanostructure. We confirm that this optically confined probe increases image contrast and is able to resolve features smaller than the far-field diffraction limit. Furthermore, by using an array of dual-wavelength diffractive microlenses, we demonstrate the feasibility of parallelizing this approach. Compared to previous approaches, our technique is not limited to fluorescence imaging.

This letter describes the formation of two-dimensional (2D) crystals of dipolar particles (TN) made of electrostatically charged, joined, millimeter-scale Teflon (T) and nylon-6,6 (N) spheres, and the separation of these crystals, as a distinct phase, from a mixture of TN and similar, capacitively charged particles that were coated with gold (Au2). The extent of separation increased with increasing amplitude of agitation, and with decreasing density of particles. Above a threshold in the amplitude of agitation, the crystals broke apart and the particles remixed. This system is a 2D model of the nucleation of crystals of polar molecules in a polarizable liquid.

The synthesis and optical properties of several phosphorescent conjugated poly(phenylene)s containing cyclometalated square-planar platinum (II) complexes are reported. These electronic polymers were synthesized via Suzuki cross-coupling of a dibromophenylpyridine-ligated Pt(II) complex with a fluorene diboronic ester. Their optical properties are characterized by relatively strong orange room-temperature phosphorescence with well-resolved vibronic structure in both frozen 2-methyltetrahydrofuran glass and room-temperature fluid solution. Time-resolved phosphorescence spectroscopy has shown that the polymers have excited state lifetimes of approximately 14 μs. These optical properties of the oligomers and polymers are contrasted with those of small model complexes, the optical properties of which have a strong dependence on the identity of the β-diketonate ligand used. The potential utility of phosphorescent conjugated polymers is illustrated by examination of the diffusive quenching due to oxygen as a function of molecular structure.