FRET Based Two Photon Three Dimensional Optical Data Storage.

We solved a major problem in three-dimensional optical data storage using photochronic materials, thus enabling multi-layer, high-density data recording and readout without erasing the data for write-once, read many (WORM) optical data storage

Organic nanoparticulate photochromes

Photochromic organic dyes can be widely used in materials for optically rewritable data storage, photonic switches, memories, sensors, or actuators. In recent years photochromic materials based on nanoparticles became particularly focused, since they can be dispersed in colloidal aqueous suspensions or incorporated in thin films, avoiding problems of light scattering or shallow light penetration in bulk materials. Spiropyrans, spirooxazines and diarylethenes were by far the most researched photochromes in nanoparticulate systems. Great effort was made to investigate photochromic dyes incorporated into organic nanoparticles via self-assembly strategies, covalent linkage or dispersion of the molecular species in polymers (doping). Nanoparticles composed of solely photochromic dyes were prepared by laser ablation and reprecipitation techniques. Photochromic dyes were microencapsulated by self-assembly, soap free-, emulsion/microemulsion/miniemulsion or free radical- (co)polymerization. Sol-gel processing from silane precursors to poly(organo)siloxane matrix is a common method to synthesize doped or core-shell photochromic organogels. Coloured forms of some photochromes display fluorescence; however, a more effective strategy for fluorescence modulation with photochromic molecules is integrating them, covalently or noncovalently, with a separate fluorophore in the same nanoparticles. These photoresponsive nanoparticles may find applications particularly in biological fields such as cell labelling and bioimaging. The purpose of this review is to summarize the preparation methods of organic nanoparticles containing photochromic dyes and to investigate their typical properties derived from their nanoparticulate character

Photoactive Materials: Synthesis, Applications and Technology

This book presents a collection of 13 original research articles that focus on the science of light–matter interaction. This area of science has been led to some the greatest accomplishments of the past 100 years, with the discovery of materials that perform useful operations by collecting light or generating light from an outside stimulus. These materials are at the center of a multitude of technologies that have permeated our daily life; every day we rely on quantum well lasers for telecommunication, organic light emitting diodes for our displays, complementary metal–oxide–semiconductors for our camera detectors, and of course a plethora of new photovoltaic cells that harvest sunlight to satisfy our energy needs. In this book, top-rated researchers present their latest findings in the field of nano-particles, plasmonics, semi-conductors, magneto-optics, and holography

Analysis of phase patterns in photochromic polyurethanes by a holographic approach

Photochromic polyurethanes based on diarylethene units show a large reversible modulation of refractive index in the Vis-NIR spectral region. The change of refractive index in the material is easily induced by visible laser illumination, without any optical or chemical post-process. In this paper, patterns at the micron scale range have been written by a suitable direct laser writing machine and characterized at 1550 nm by means of a digital holographic approach. The refractive index profile has been retrieved, its dependence on the film thickness and writing speed was shown. The writing process has also been modelled by means of a kinetic model, showing theoretically the dependence of the pattern width and profile on the writing conditions. It is demonstrated that the photochromic films are suitable for developing a reconfigurable platform for complex phase patterns working in the NIR. © 2015 Optical Society of America

A new light-responsive resistive random-access memory device containing hydrogen-bonded complexes.

Acknowledgements: TSV acknowledges financial support from the Ministry of Higher Education of Malaysia through the Fundamental Research Grant Scheme [FP079-2018A]. AR acknowledges Ministerio de Economía y Competitividad (MINECO) for his PhD grant BES-2015-071235, under the project MAT2014-55205-P. VMA acknowledges the University Malaya for the grant RF004B-2018. AMF would like to thank the Royal Academy of Engineering, U.K., for the grant NRCP1516/4/61 (Newton Research Collaboration Programme), the University of Aberdeen, for the award of the grant SF10192, the Carnegie Trust for the Universities of Scotland, for the Research Incentive Grant RIG008586, the Royal Society and Specac Ltd., for the Research Grant RGS\R1\201397, and the Royal Society of Chemistry for the award of a mobility grant (M19-0000). AMF and TSV further acknowledge University Malaya for travelling support.Peer reviewedPostprin

Photochromic organic-inorganic hybrid materials

Este artículo ha sido publicado como parte del número especial dedicado a Hybrid materialsPhotochromic organic-inorganic hybrid materials have attracted considerable attention owing to their potential application in photoactive devices, such as optical memories, windows, photochromic decorations, optical switches, filters or non-linear optics materials. The growing interest in this field has largely expanded the use of photochromic materials for the purpose of improving existing materials and exploring new photochromic hybrid systems. This tutorial review summarizes the design and preparation of photochromic hybrid materials, and particularly those based on the incorporation of organic molecules in organic-inorganic matrices by the sol-gel method. This is the most commonly used method for the preparation of these materials as it allows vitreous hybrid materials to be obtained at low temperatures, and controls the interaction between the organic molecule and its embedding matrix, and hence allows tailoring of the performance of the resulting devices.Ministerio de Ciencia e Innovacion MAT2008-00010/NANPeer reviewe

Halide Perovskites as Emerging Anti-Counterfeiting Materials Contribute to Smart Flow of Goods

The counterfeiting of goods is a fast-growing issue worldwide, being a risk to human health, financial safety, and national security. Customized anti-counterfeiting patterning technologies enable unclonable tags on products, which ensure the reliable and convenient flow of goods such as daily foods, prescription medicines, and value-added components. In this chapter, we start with the introduction of recent advances of anti-counterfeiting technologies that generate unique physical tags on products for encryption and information storage. Various halide perovskite-based materials and their fabrication techniques for unreplicable luminescent patterns are then discussed, with a particular focus on the intelligent encoding principles that correlate with the chromism and other special optical readout of materials. The multilevel anti-counterfeiting functions that allow high-throughput authentication of products within a single tag are also exemplified, through which the increasing security demands can be fulfilled. We finally discuss the current issues encountered by perovskite anti-counterfeiting technologies and outline their future directions toward smarter and safer flow of goods

An investigation of the performance of photochromic dyes and their application to polyester and cotton fabrics

Six commercial photochromic dyes were applied to polyester and, to a lesser extent, cotton fabrics by different dyeing and printing methods. The photochromic performance of the dyed and printed fabrics was investigated in terms of the degree of photocoloration, background colour, fading characteristics, fatigue resistance and storage stability. A traditional aqueous-based disperse dyeing method was used to apply the photochromic dyes to polyester fabric. Solvent-based dyeing methods also were investigated for application of the photochromic dyes to polyester fabric. Solvent-based inks were formulated and applied to polyester and cotton fabrics by digital inkjet printing. The photochromic performance and colour fastness to light and washing of the photochromic fabrics were evaluated and comparison made. UV/visible spectra of the commercial photochromic dyes in a range of solvents were obtained and interpreted in terms of solvent polarity. On the basis of this study, the photochromic performance of the fabrics was improved by selecting the appropriate application solvents which transferred minimum background colours onto the fabrics. A new method of evaluating lightfastness of photochromic fabrics was established, aimed at replacing the conventional method by an instrumental method. This method was based on comparing the decrease in the degree of photocoloration of photochromic fabrics after light exposure with measured values of the colour differences of the blue wool references after fixed periods of light exposure. Two photochromic dyes were synthesized by azo coupling of a spironaphtho[2,1-b]oxazine with diazonium salts obtained from p-nitroaniline, and m-nitroaniline. Molecular modeling of the new photochromic systems, which are referred to as azospirooxazine dyes, showed that the dyes were predicted to have the potential to show photochromism. Thus, the photochromism of the azospirooxazine dyes in a range of solvents was investigated. The investigations showed that the dyes performed differently in different solvents in terms of the hue, the rate of the photochromic colour change and the colour reversibility

Nonlinear Excitation of Photoactivated Molecules: Two-Photon Absorption Spectroscopy, Dynamics, and Quantum Yields

Higher-lying excited electronic states of model, photoactivated molecules are studied using nonlinear excitation to explore the electronic spectroscopy, excited-state dynamics, and reaction quantum yields. The photoactivated molecules studied in this dissertation include two photochromic molecules, stilbene and 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluoro-cyclopentene, that reversibly convert between different isomers following irradiation, as well as a photoactivated protecting group, para-hydroxyphenacyl, that photochemically releases a bound substrate. Studying higher-lying excited states above S1 following nonlinear excitation provides information about the initially excited state, the subsequent excited-state dynamics, and the reaction quantum efficiency. Much less is known about the higher-lying excited states as compared to the well-studied ground and lowest-lying excited states, which motivates the work in this dissertation to investigate the higher-lying excited states of photoactivated molecules following nonlinear excitation. The measurements of the higher-lying excited states reported here include a broadband pump-probe technique that is used to measure the two-photon absorption spectroscopy, as well as the excited-state dynamics following linear and nonlinear excitation of the studied photoactivated molecules. The broadband two-photon absorption spectroscopy measurements reveal the two-photon accessible states and their absolute two-photon absorption cross sections. Separate measurements of the excited-state dynamics and of the reaction quantum yields following nonlinear excitation collectively provide information about the behavior of the higher-lying excited-states, and how the identity of the excited states affect the outcome of the photochemical reactions. Probing the spectroscopy, dynamics, and quantum yields of the studied photoactivated molecules is important to develop a fundamental understanding of photochemical reactions from higher-lying excited states. The spectroscopy, dynamics, and quantum yield measurements in this dissertation can also serve as new benchmarks for computational studies of these model molecules

Die photochrome Ringöffnungsreaktion der Indolylfulgide

Fulgide gehören zu den photochromen molekularen Schaltern auf der Basis eines 6-elektrozyklischen Systems. Ihre ausgeprägte Photochromie wird von einer photoinduzierten, reversiblen Ringöffnung bestimmt: Das farbige Isomer mit geschlossenem Ring wird dabei durch sichtbares Licht in ein farbloses, offenes Isomer überführt. Mithilfe der transienten Absorptionsspektroskopie im UV/VIS und im mittleren IR konnten in der vorliegenden Arbeit entscheidende Fortschritte im Verständnis der perizyklischen Ringöffnung von Fulgiden und von chemisch nahe verwandten Fulgimiden erreicht werden. Erstmals konnte die Kinetik der Ringöffnungsreaktion im Detail vermessen und damit der Reaktionsweg der Ringöffnung aufgeklärt werden: Die Messergebnisse deuten auf einem Modell mit einer direkten photochemischen Umwandlung auf der Zeitskala von wenigen Pikosekunden und ohne langlebige Intermediate hin. Nach Anregung des geschlossenen Isomers in den angeregten S2-Zustand alternative Reaktionspfade abläuft. Die Mehrheit der S2-angeregten Moleküle beschreiten einen direkten Reaktionsweg, während nur etwa 40% die bekannte Abfolge (Kasha-Regel) der molekularen Prozesse für Photoreaktionen aus höheren elektronischen Zuständen durchlaufen: Zunächst erfolgt eine Relaxation in den niedrigsten elektronisch angeregten Zustand und von dort die „normale“ S1-Photochemie. Weiter werden die Auswirkungen optischer und thermischer Überschussenergie auf die Quanteneffizienz der Ringöffnungsreaktion der Fulgide untersucht. Ein einfaches Modell auf der Basis der Arrhenius-Gleichung wird entwickelt, das davon ausgeht, dass beide Arten der Energiezufuhr eine äquivalente photochemische Wirkung zeigen, dass also optische Überschussenergie sehr schnell thermalisiert. Zentrales Element ist dabei ein Konversionskoeffizient, der es in linearer Näherung erlaubt, optische Überschussenergie in zusätzliche thermische Energie umzurechnen. Im Zusammenhang mit potentiellen Anwendungen ist es gelungen, den Prototyp eines extrem schnellen, rein optischen Schreib/Lese/Lösch/Lese Operationszyklus auf molekularer Basis zu realisieren. Dieses „proof of principle“ Experiment demonstriert, dass die einzelnen Elemente des Zyklus basierend auf photochromen Fulgiden mit einer Taktrate von 250 GHz kombiniert werden können.Fulgides belong to the class of photochrome molecular switches based on a 6-electron system. Their pronounced photochromism is governed by a photoinduced reversible ring opening: The colored ring-closed isomer is converted by visible light into a colorless ringopened isomer. Using transient absorption spectroscopy in the ultraviolett, visible and nearinfrared spectral range decisive progress has been achieved in understanding the pericyclic cycloreversion reaction of fulgids and the chemically close related fulgimids. For the first time the kinetics of the ring-opening reaction could be measured in detail and thereby the reaction pathway could be elucidated: the experimental results can be interpreted in a model with a direct photochemical transition on the timescale of a view picoseconds without long-lived intermediates. After excitation of the ring-closed isomer into the higher excited S2-state, that though the same overall photoreaction occurs as in comparison with S1-excitation, an alternative reaction pathway appears. The majority of the S2-excited molecules passes this reaction pathway and only about 40% step through the most common succession („Kasha rule“) of the molecular processes for photoreactions from higher electronically excited states. Firstly a relaxation into the lowest excited state (S1) occurs and subsequently the normal S1-photochemistry follows. Furthermore, the effect of optical and thermal excess energy on the quantum yield of the fulgide ring opening reaction is investigated. A simple model is developed, which is based on the equivalent photochemical effect of these two kinds of additional energy. Thereby the centralelement is a conversion coefficient that allows for translation (in a linear approximation) of optical excess energy into additional thermal energy. In terms of applications the prototype of an ultrafast all-optical write/read/erase/read operation cycle based on photchromic fulgides was realized. This „proof of principle“ experiment demonstrates that the single elements of the cycle can be combined with a clock rate of at least 250 GHz. For future application concepts molecular bits based on photochromic fulgides represent attractive building blocks