All‐Optical Operation Cycle on Molecular Bits with 250‐GHz Clock‐Rate Based on Photochromic Fulgides

The prototype operation of an ultrafast write–readout–erase–readout cycle of an all‐optical system based on photochromic indolylfulgides is demonstrated. In the employed dye the molecular structure is switched using light of different wavelengths between two thermally stable states to allow binary encoding of information. Non‐destructive readout of the bit states using infrared light completes the scheme of an all‐optical memory. For ultrafast operation femtosecond light pulses are applied and it is demonstrated that two consecutive write/erase processes separated by less than 4 ps still allow the defined readout of the bit state. The short time between the write/erase and readout actions demonstrates that an all‐optical data storage system based on indolylfulgides may be operated at memory clock rates that exceed 250 GHz.     

Poly(dithienylethene‐alt‐1,4‐divinylenephenylene)s: Increasing the Molecular Weights in Diarylethene Photochromic Polymers

Thermally irreversible, photochromic dithienylethene‐alt‐dihexyloxyphenylenevinylene and dithienylethene‐alt‐didodecyloxyphenylenevinylene copolymers have been synthesized via the Horner and Wittig reactions, respectively. Both polymers are photochromic in solution and in the solid state. Electronic spectra show that the materials are highly conjugated in both states and the large π‐delocalization along the main chain when the diarylethene moiety is in the closed form gives a decrease of the ring‐opening quantum yield. The increase in molecular weight relative to other backbone dithienylethene polymers allows the preparation of good quality films without the use of supporting polymer matrices; this is an important achievement for the technological application of these photochromic materials.     

Synthesis of Novel Photochromic Films by Oxidation Polymerization of Diarylethenes Containing Phenol Groups

We report the synthesis of some diarylethene derivatives attached to phenol moieties, which show remarkable photochromic reactions. A dithienylethene group attached to the o‐phenol moiety (1,2‐bis[2,4‐dimethyl‐5‐(o‐hydroxyphenyl)‐3‐thienyl]hexafluorocyclopentene) was polymerized according to Hay's method; the resulting film was insoluble to any solvents, and showed no absorption band attributable OH group in its IR spectrum. Isomeric dithienylethenes attached to m‐ and p‐phenol moieties did not form films under the same oxidation conditions, but instead formed films by copolymerization with 4,4′‐dihydroxyphenyl ether. Although the homopolymer film and copolymer films showed reversible photochromic reactions by alternate irradiation with UV and visible light, the coloration was not remarkable. Polymerization of closed‐ring isomers of the dithienylethenes did not give pre‐polymers and instead decomposed, while the closed‐ring isomer of a bisbenzothienylethene derivative attached to the o‐phenol moiety (1,2‐bis[2‐methyl‐6‐(o‐hydroxyphenyl)‐1‐benzothiophen‐3‐yl]hexafluorocyclopentene) formed a polymer film by the same procedure. This polymer film showed a remarkable photochromic reaction, indicating the photo‐reactive conformation was fixed in polymer matrix, and X‐ray diffraction measurements show that the film is in the amorphous phase. The photochromic reaction can also be monitored by IR spectroscopy, making it applicable for non‐destructive read‐out recording films.     

Fluorescence Modulation in Polymer Bilayers Containing Fluorescent and Photochromic Dopants

We have identified viable operating principles for the modulation of optical signals under the influence of optical stimulations. They are based on the overlap between the emission bands of a fluorescent compound and the absorption bands of one of the two forms of a bistable photochromic switch. Under these conditions, the photoinduced interconversion of the two states of the photochrome modulates efficiently the emission intensity of the fluorophore. We have implemented this mechanism for intermolecular fluorescence modulation with multilayer structures. They consist of two quartz plates sandwiching two overlapping polymer layers. One of the polymers is doped with a fluorescent benzofurazan. The other contains a photochromic spiropyran. The multilayer assembly is operated with two light sources. One of them is centered at the excitation wavelength of the fluorophore, where neither of the two states of the photochrome absorbs. The other light source is switched between ultraviolet and visible wavelengths to induce the interconversion between the two states of the photochrome. The light emitted by the fluorescent component has to propagate through the photochromic layer before reaching a detector. It can do so efficiently for only one of the two states of the photochrome. It follows that a measurement of the light intensity reaching the detector can read the state of the photochromic switch, which in turn is written and erased with optical stimulations. Thus, our strategy for all‐optical processing can be used to store and retrieve binary digits, as well as to implement optical inversion, with the aid of engineered molecule‐based components.     

ErIII‐Cored Complexes Based on Dendritic PtII–Porphyrin Ligands: Synthesis,Near‐IR Emission Enhancement,and Photophysical Studies

A series of stable and inert complexes with Er^III cores and dendritic Pt^II‐porphyrin ligands exhibit strong near‐IR (NIR) emission bands via highly efficient energy transfer from the excited triplet state of the Pt^II‐porphyrin ligand to Er³⁺ ions. The NIR emission intensity of thin films of Er^III complexes at 1530 nm, originating from 4f–4f electronic transitions from the first excited state (⁴I_13/2) to the ground state (⁴I_15/2) of the Er³⁺ ion, is dramatically enhanced upon increasing the generation number (n) of the aryl ether dendrons because of site‐isolation and light‐harvesting (LH) effects. Attempts are made to distinguish the site‐isolation effect from the LH effect in these complexes. Surprisingly, the site‐isolation effect is dominant over the LH effect in the Er³⁺‐[Gn‐PtP]₃(terpy) (terpy: 2,2′:6′,2″‐terpyridine) series of complexes, even though the present dendrimer systems with Er^III cores have a proper cascade‐type energy gradient. This might be due to the low quantum yield of the aryl ether dendrons. Thus, the NIR emission intensity of Er³⁺‐[G3‐PtP]₃(terpy) is 30 times stronger than that of Er³⁺‐[G1‐PtP]₃(terpy). The energy transfer efficiency between the Pt^II‐porphyrin moiety in the dendritic Pt^II‐porphyrin ligands and the Ln³⁺ ion increases with increasing generation number of the dendrons from 12–43 %. The time‐resolved luminescence spectra in the NIR region show monoexponential decays with a luminescence lifetime of 0.98 μs for Er³⁺‐[G1‐PtP]₃(terpy), 1.64 μs for Er³⁺‐[G2‐PtP]₃(terpy), and 6.85 μs for Er³⁺‐[G3‐PtP]₃(terpy) in thin films of these complexes. All the Er^III‐cored dendrimer complexes exhibit excellent thermal stability and photostability, and possess good solubility in common organic solvents.     

1,2‐Dithienylethene Photochromes and Non‐destructive Erasable Memory

Monitoring changes in ultraviolet‐visible (UV‐vis) absorption is not a viable method to process information for photochromic memory media due to the readout signal interfering with the photochromism. Only by monitoring the changes in other photophysical properties accompanying the photoisomerization reaction (refractive index, optical rotation, or luminescence, for example) can non‐destructive, all photon‐mode photochromic memory be realized. We have investigated several such systems based on 1,2‐dithienylcyclopentene derivatives, which have a backbone that we consider to be currently the most promising of the photochromes. The two readout signals highlighted in this article are luminescence and optical rotation. The luminescent systems rely on porphyrinic chromophores tethered to the photochrome directly or through dative bonds. When the macrocycles are irradiated with light at wavelengths outside the absorption range of the photochrome, luminescence is only observed when the 1,2‐dithienylcyclopentene backbone exists in its open‐state. The self‐assembly of a chiral photochromic metallo‐helicate allows for stereoselective ring‐closing of the 1,2‐dithienylcyclopentene backbone providing a change in optical rotation that can be used as a readout signal. In the article, we also describe the use of ring‐opening metathesis polymerization (ROMP) to fabricate well‐ordered photochromic homopolymers possessing identical photochromic properties as their monomers.     

Thermally Enhanced Visible‐Light Photochromism of Phosphomolybdic Acid–Polyvinylpyrrolidone Hybrid Films

Phosphomolybdic acid/polyvinylpyrrolidone hybrid films were found to show visible light photochromism. It is identified that the intra‐supramolecular charge transfer between the inorganic and organic molecules is responsible for the visible‐light coloration. Interestingly, the films show photo‐memory and thermal activation. The films show a small change in absorbance after being irradiated with visible light for a short time, and the coloration can be enhanced greatly by subsequent thermal treatment. Electrical measurements indicate that the conductivity of the film increases after the brief irradiation, which promotes transfer of the electrons induced by the thermal treatment.     

Reversible Diffraction Efficiency of Photochromic Polymer Gratings Related to Photoinduced Dimensional Changes

In this Full Paper, the possibility of reversibly changing the diffraction efficiency of gratings, fabricated by soft molding lithography on polymer films, containing photochromic molecules, is demonstrated. In particular, alternating UV and visible laser irradiation of the gratings causes the doped photochromic molecules to undergo transformations, which induce reversible dimensional changes to the samples. As a result, reversible changes are monitored in the intensity of the beams of a diode laser, transmitted and diffracted from the gratings. These changes affect the diffraction efficiency, which is increased upon irradiation with UV and decreased after irradiation with visible laser light. Such gratings are promising candidates for the fabrication of modern optical components such as optical switching devices.     

Magnetic Multi‐Functional Nano Composites for Environmental Applications

A novel concept is proposed to synthesize a new class of composites featuring magnetic, molecular sieve and metallic nanoparticle properties. These multi‐functional materials have potential applications as recyclable catalysts, disinfectants and sorbents. The magnetic property enables effective separation of the spent composites from complex multiphase systems for regeneration and recycle, safe disposal of the waste and/or recovery of loaded valuable species. The zeolite molecular sieve provides a matrix which supports a remarkably new, simple, efficient and economical method to make stable, supported silver nanoparticles by silver ion exchange and controlled thermal reduction. The silver nanoparticles generated in this way have excellent properties such as high reactivity and good thermal stability without aggregation, which act as nano reactors for desired functionality in a wide range of applications. Magnetic component (Fe₃O₄), molecular sieve matrix (zeolite) and silver nanoparticles generated by ion exchange followed by controlled reduction, together form this unique novel composite with designed functions. It represents a practically operational, economical, sustainable and environmentally friendly new advanced functional material. This paper focuses on the novel synthesis and characterization of the composite, with an example of applications as sorbents for the removal of vapor‐phase mercury from the flue gas of coal‐fired power plants.     

Multi‐Stimuli Responsive Hydrogel Cilia

Large arrays of high aspect ratio, artificial hydrogel based cilia that can respond to multiple stimuli are produced by means of micro‐fabrication techniques. The cilia operate in aqueous solutions and are sensitive to pH, electric and/or magnetic fields. The biomimetic system combines both sensing and motility. Detection of changes in environment, such as a decrease in pH, triggers a collective response, to an external time‐dependent magnetic field.     

Novel Chromogenic Esters of ortho‐Phenylazonaphthols

We have prepared the photo‐labile benzoic acid esters and the acid‐labile tert‐butoxycarbonyl esters of Sudan I and Sudan Red B, two representatives of the ortho‐phenylazonaphthol dye family, exhibiting hydroxyazo–hydrazone tautomerism with the hydrazone as the strongly favored form. The chromophores obtained are “locked” in an exclusive azo configuration and exhibit absorbance spectra which are dramatically blue‐shifted (more than 100 nm) and have strongly reduced extinction coefficients when compared to their parent chromophores. Thus, the esters of the orange dye Sudan I exhibit an absorption maximum in the ultraviolet (UV) regime, and the esters of the red dye Sudan Red B appear yellow. Depending on the nature of the ester moiety, by irradiation with UV light or by exposure to preferentially photochemically released acidic species at elevated temperatures, these esters can be reverted to the parent, highly tinctured Sudan I and Sudan Red B, respectively. Unlike conventional chromogenic systems, these dyes are compatible with melt‐processible polymers and do not require any wet‐chemical development. In polymer films comprised of these chromogenic dyes, color patterns can be produced directly by masked irradiation. We here report on the synthesis, spectral properties, and conversion kinetics of these novel chromogenic dyes, which may be potentially suitable for marking and labeling goods in a lithographic process and for optical data storage and sensing applications.     

Tuning the Thermal Relaxation of a Photochromic Dye in Functionalized Mesoporous Silica

In this study, it is shown that the kinetics of the back‐switching reaction of a photochromic spirooxazine dye encapsulated in mesoporous silica materials can be significantly influenced both by the space available to the dye molecules and by the functionalization of the silica wall. Steric hindrance of the ring‐closing process due to high dye content or small pore size leads to a slow fading speed of the irradiated dye species. Further, the density of surface silanol‐groups present at the silica walls has an effect on the switching behavior of the dye because of their ability to stabilize the zwitterionic merocyanine isomers, thereby slowing the fading process from the open to the closed form. This stabilization effect is further enhanced in the presence of acidic functional groups, while, in contrast, basic functional groups reduce the stabilization of the open‐from dye isomers, and thus a faster decay of the irradiated species is observed. Control over the fading speed of photochromic dyes is interesting for applications requiring a particularly fast or slow fading speed.     

Photoswitchable Spirobenzopyran‐ Based Photochemically Controlled Photonic Crystals

We have developed a photochemically controlled photonic‐crystal material by covalently attaching spiropyran derivatives to polymerized crystalline colloidal arrays (PCCAs). These PCCAs consist of colloidal particles that self‐assemble into crystalline colloidal arrays (CCAs), which are embedded in crosslinked hydrogels. Photoresponsive PCCAs were made two ways: 1) by functionalizing the hydrogel network with spiropyran derivatives, and 2) by functionalizing the colloidal particles with spiropyran derivatives. These materials can diffract light in the UV, visible, or near‐IR spectral regions. The diffraction of the PCCAs is red‐shifted by exciting the spiropyran with UV light. Alternatively, the diffraction is blue‐shifted by exciting the spiropyran with visible irradiation. Thus, this material acts as a memory storage material where information is recorded by illuminating the PCCA and information is read out by measuring the photonic‐crystal diffraction wavelength. UV excitation forms the open spiropyran form while visible excitation forms the closed spiropyran form. The diffraction shifts result from changes in the free energy of mixing of the PCCA system as the spiropyran is photoexcited to its different stable forms.     

Optical Power Limiters Based on Colorless Di‐, Oligo‐, and Polymetallaynes: Highly Transparent Materials for Eye Protection Devices

The synthesis, characterization, and photophysics of a series of solution‐processable and tractable di‐, oligo‐, and polymetallaynes of some group 10–12 transition metals are presented. Most of these materials are colorless with very good optical transparencies in the visible spectral region and exhibit excellent optical power limiting (OPL) for nanosecond laser pulse. Their OPL responses outweigh those of the state‐of‐the‐art reverse saturable absorption dyes such as C₆₀, metalloporphyrins, and metallophthalocyanines that are all associated with very poor optical transparencies. On the basis of the results from photophysical studies and theoretical calculations, both the absorption of triplet and intramolecular charge‐transfer states can contribute to the enhancement of the OPL properties for these materials. Electronic influence of the type, spatial arrangement, and geometry of metal groups on the optical transparency/nonlinearity optimization is evaluated and discussed in detail. The positive contribution of transition metal ions to the OPL of these compounds generally follows the order: Pt > Au > Hg > Pd. The optical‐limiting thresholds for these polymetallaynes can be as low as 0.07 J cm^–2 at 92 % linear transmittance and these highly transparent materials manifest very impressive figure of merit σ_ex/σ_o values (up to 22.48), which are remarkably higher than those of the benchmark C₆₀ and metal phthalocyanine complexes. The present work demonstrates an attractive approach to developing materials offering superior OPL/optical transparency trade‐offs and these metallopolyynes are thus very promising candidates for use in practical OPL devices for the protection of human eyes and other delicate optical sensors.     

Solution‐Processible Multi‐component Cyclometalated Iridium Phosphors for High‐Efficiency Orange‐Emitting OLEDs and Their Potential Use as White Light Sources

The synthesis and photophysical studies of several multifunctional phosphorescent iridium(III) cyclometalated complexes consisting of the hole‐transporting carbazole and fluorene‐based 2‐phenylpyridine moieties are reported. All of them are isolated as thermally and morphological stable amorphous solids. Extension of the π‐conjugation through incorporation of electron‐pushing carbazole units to the fluorene fragment leads to bathochromic shifts in the emission profile, increases the highest occupied molecular orbital levels and improves the charge balance in the resulting complexes because of the propensity of the carbazole unit to facilitate hole transport. These iridium‐based triplet emitters give a strong orange phosphorescence light at room temperature with relatively short lifetimes in the solution phase. The photo‐ and electroluminescence properties of these phosphorescent carbazolylfluorene‐functionalized metalated complexes have been studied in terms of the coordinating position of carbazole to the fluorene unit. Organic light‐emitting diodes (OLEDs) using these complexes as the solution‐processed emissive layers have been fabricated which show very high efficiencies even without the need for the typical hole‐transporting layer. These orange‐emitting devices can produce a maximum current efficiency of ～ 30 cd A^–1 corresponding to an external quantum efficiency of ～ 10 % ph/el (photons per electron) and a power efficiency of ～ 14 lm W^–1. The homoleptic iridium phosphors generally outperform the heteroleptic counterparts in device performance. The potential of exploiting these orange phosphor dyes in the realization of white OLEDs is also discussed.     

Nanocrystalline Transition‐Metal Oxide Spheres with Controlled Multi‐Scale Porosity

This article presents original multi‐scale porous nanocrystalline transition‐metal oxide materials (MO₂, where M = Ti, Zr, Ce) that have many potential applications. They were prepared through a one step method that combines sol–gel chemistry, multi‐scale templating approaches, aerosol processing, and specific treatments. The final material presents itself as spheres of controlled diameter, made of a periodically organized mesoporous crystalline network that surrounds spherical macropores, in which each single porosity can be easily and independently adjusted. In addition, a porosity gradient can be generated. The strategy highlighted here can be easily applied to many hierarchically structured sol–gel derived materials. Moreover, this process can easily be scaled up, which could lead to a breakthrough in the industrial production of innovative multiscale porosity materials.     

Enhancement of External Quantum Efficiency of Red Phosphorescent Organic Light‐Emitting Devices with Facially Encumbered and Bulky PtII Porphyrin Complexes

An enhancement in the external quantum efficiency (QE) of red phosphorescent organic light‐emitting devices (OLEDs) by using facially encumbered and bulky meso‐aryl substituted Pt^II porphyrin complexes is demonstrated. The maximum external QEs of phosphorescent OLEDs doped with the facially non‐encumbered Pt^II porphyrin complex 1 [5,15‐bis[4‐(4,4‐dimethyl‐2,6‐dioxacyclohexyl)phenyl]‐2,8,12,18‐tetrahexyl‐3,7,13,17‐tetramethylporphyrin platinum(II )], the facially encumbered Pt^II porphyrin complex 2 [5,15‐bis(2,6‐dimethoxyphenyl)‐2,8,12,18‐tetrahexyl‐3,7,13,17‐tetramethylporphyrinato platinum(II )], the Pt^II porphyrin complex 3 that bears bulkier 3,5‐di‐tert‐butylphenyl substituents [5,15‐bis(3,5‐di‐t‐butylphenyl)‐2,8,12,18‐tetrahexyl‐3,7,13,17‐tetramethylporphyrin platinum(II )], and the “doubly‐decamethylene‐strapped” Pt^II porphyrin complex 4 were 1, 4.2, 7.3, and 8.2 %, respectively. The trend of increasing QE values in the order of 1 < 2 < 3 < 4 may be related to facial encumbrance and steric bulkiness of meso‐aryl substituted Pt^II porphyrin complexes. Especially, in the case of the Pt^II porphyrin 4 , it is considered that the “double straps” play an important role in restricting rotational freedom of the meso‐aryl substituents. The triplet excited‐state lifetimes for Pt^II porphyrins 1 – 4 in OLEDs at an injection current density of 0.55 mA cm^–2 were 80, 103, 140, and 152 μs, respectively. We believe that the trend of increasing triplet lifetime in going from 1 to 4 is correlated with suppressing non‐radiative decay.     

A Smart Light‐Controlled Carrier Switch in an Organic Light Emitting Device

A real ON–OFF carrier switch based on a new ferrocenyl diarylethene compound (DTE‐FC) as the light‐sensitive and photoswitching layer in an organic light‐emitting device (OLED) with a multilayer sandwich structure has been prepared. This switch layer functions not only as a hole transporter but also as a good barrier block when needed, which arises from the light‐induced photochromic effect of the DTE‐FC. For the uncolored open‐ring form of DTE‐FC, no luminescence was observed despite the increase in applied voltage. On the contrary, for the colored photostationary state of DTE‐FC, which was obtained by irradiation with 365 nm light, the luminescence could be observed when the applied voltage reached 14.0 V and increased with applied voltage. Thus, the uncolored state corresponds to the OFF state of luminescence and the photostationary state corresponds to the ON state. The two states can be interconverted by control of the UV and visible light (>500 nm) irradiation.     

Cross‐Layer Resource Allocation in Multi‐interface Multi‐channel Wireless Multi‐hop Networks

In this paper, an analytical framework is proposed for the optimization of network performance through joint congestion control, channel allocation, rate allocation, power control, scheduling, and routing with the consideration of fairness in multi‐channel wireless multi‐hop networks. More specifically, the framework models the network by a generalized network utility maximization (NUM) problem under an elastic link data rate and power constraints. Using the dual decomposition technique, the NUM problem is decomposed into four subproblems — flow control; next‐hop routing; rate allocation and scheduling; power control; and channel allocation — and finally solved by a low‐complexity distributed method. Simulation results show that the proposed distributed algorithm significantly improves the network throughput and energy efficiency compared with previous algorithms.     

Multi‐Site Functionalization of Protein Scaffolds for Bimetallic Nanoparticle Templating

The use of biological scaffolds to template inorganic material offers a strategy to synthesize precise composite nanostructures of different sizes and shapes. Proteins are unique biological scaffolds that consist of multiple binding regions or epitope sites that site‐specifically associate with conserved amino acid sequences within protein‐binding partners. These binding regions can be exploited as synthesis sites for multiple inorganic species within the same protein scaffold, resulting in bimetallic inorganic nanostructures. This strategy is demonstrated with the scaffold protein clathrin, which self‐assembles into spherical cages. Specifically, tether peptides that noncovalently associate with distinct clathrin epitope sites, while initiating simultaneous synthesis of two inorganic species within the assembled clathrin protein cage, are designed. The flexibility and diversity of this unique biotemplating strategy is demonstrated by synthesizing two types of composite structures (silver–gold mixed bimetallic and silver–gold core–shell nanostructures) from a single clathrin template. This noncovalent, Template Engineering Through Epitope Recognition, or TEThER, strategy can be readily applied to any protein system with known epitope sites to template a variety of bimetallic structures without the need for chemical or genetic mutations.