二甲基二氢芘类光致变色化合物及其光开关性质

介绍了二甲基二氢芘类化合物特殊的逆光致变色性质,讨论了内外取代基、间隔基以及稠合基团等因素对二甲基二氢芘光致变色性质的影响,综述了该类化合物在光学开关和信息的光化学读出等应用方面的研究状况,并展望了二氢芘类光致变色化合物的研究前景。     

Rational Design in Photopharmacology with Molecular Photoswitches

Photopharmacology is an attractive approach for achieving targeted drug action with the use of light. In photopharmacology, molecular photoswitches are introduced into the structure of biologically active small molecules to allow for the optical control of their potency. Going beyond trial and error, photopharmacology has progressively applied rational drug design methodologies to devise light-controlled bioactive ligands. In this review, we categorize photopharmacological efforts from the standpoint of medicinal chemistry strategies, focusing on diffusible photochromic ligands modified with photoswitches that operate through E-Z bond isomerization. In the vast majority of cases, photoswitchable ligands are designed as analogs of existing compounds, through a variety of approaches. By analyzing in detail a comprehensive list of instructive examples, we describe the state of the art and discuss future opportunities for rational design in photopharmacology.     

Synthesis and characterization of novel bifunctional hemithioindigo chromophores

[structure: see text] General methods for the synthesis of novel bifunctional hemithioindigo (HT) compounds, e.g., omega-amino acid derivatives, are presented. The photochromic properties of the photoswitches have been characterized by UV-vis and (1)H NMR spectroscopy.     

Electrical properties of photochromic organic systems (review)

The results of studying the electrical properties of organic photochromic systems based on diarylethenes, spiropyrans, spirooxazines, and azo compounds have been analyzed. It has been shown that diarylethenes have promise for use in photoswitches of various types that reversibly and simultaneously change the spectral and electrical properties when exposed to light.     

Hydrazone Photoswitches for Structural Modulation of Short Peptides

Molecules that undergo light-driven structural transformations constitute the core components in photoswitchable molecular systems and materials. Among various families of photoswitches, photochromic hydrazones have recently emerged as a novel class of photoswitches with superb properties, such as high photochemical conversion, spectral tunability, thermal stability, and fatigue resistance. Hydrazone photoswitches have been adopted in various adaptive materials at different length scales, however, their utilization for modulating biomolecules still has not been explored. Herein, we present new hydrazone switches that can photomodulate the structures of short peptides. Systematic investigation on a set of hydrazone derivatives revealed that installation of the amide group does not significantly alter the photoswitching behaviors. Importantly, a hydrazone switch comprising an upper phenyl ring and a lower quinolinyl ring was effective for structural control of peptides. We anticipate that this work, as a new milestone in the research of hydrazone switches, will open a new avenue for structural and functional control of biomolecules.     

Reversible Photoswitching of Isolated Ionic Hemiindigos with Visible Light

Indigoid chromophores have emerged as versatile molecular photoswitches, offering efficient reversible photoisomerization upon exposure to visible light. Here we report synthesis of a new class of permanently charged hemiindigos (HIs) and characterization of photochemical properties in gas phase and solution. Gas-phase studies, which involve exposing mobility-selected ions in a tandem ion mobility mass spectrometer to tunable wavelength laser radiation, demonstrate that the isolated HI ions are photochromic and can be reversibly photoswitched between Z and E isomers. The Z and E isomers have distinct photoisomerization response spectra with maxima separated by 40–80 nm, consistent with theoretical predictions for their absorption spectra. Solvation of the HI molecules in acetonitrile displaces the absorption bands to lower energy. Together, gas-phase action spectroscopy and solution NMR and UV/Vis absorption spectroscopy represent a powerful approach for studying the intrinsic photochemical properties of HI molecular switches.     

Photocontrol of peptide secondary structure through non-azobenzene photoswitches

The rapidly expanding field of photoswitchable biomolecules is a major frontier in scientific research and provides unparalleled opportunities for studying biological pathways and disease progression. In particular, the development of photochromic peptides has delivered both scientific tools and candidates for photopharmaceuticals. The action and function of the peptide can be remotely altered using light, allowing detection of its biological role in complex biological settings, while also enabling folding studies that provide greater understanding of protein structure dynamics. In this review we provide a key, comprehensive overview of the different types of photoswitches that have been used to control peptide structure, excluding the already extensively reviewed azobenzene. This will help address the question as to which synthetic photoswitch to use in a given study.     

新型双螺噁嗪分子的合成及性能

设计合成了3个双螺噁嗪化合物, 采用核磁共振谱、红外光谱和高分辨质谱对这些化合物进行了表征. 测试了光照前后化合物在不同溶剂中的紫外吸收光谱、荧光光谱以及在高分子薄膜中的消色动力学曲线. 结果表明, 目标化合物均具有良好的光致变色性能和耐疲劳度, 在材料、分子开光及生物探针领域有潜在的应用前景.     

Cooperative and Orthogonal Switching in the Solid State Enabled by Metal-Organic Framework Confinement Leading to a Thermo-Photochromic Platform

Cooperative behavior and orthogonal responses of two classes of coordinatively integrated photochromic molecules towards distinct external stimuli were demonstrated on the first example of a photo-thermo-responsive hierarchical platform. Synergetic and orthogonal responses to temperature and excitation wavelength are achieved by confining the stimuli-responsive moieties within a metal–organic framework (MOF), leading to the preparation of a novel photo-thermo-responsive spiropyran-diarylethene based material. Synergistic behavior of two photoswitches enables the study of stimuli-responsive resonance energy transfer as well as control of the photoinduced charge transfer processes, milestones required to advance optoelectronics development. Spectroscopic studies in combination with theoretical modeling revealed a nonlinear effect on the material electronic structure arising from the coordinative integration of photoresponsive molecules with distinct photoisomerization mechanisms. Thus, the reported work covers multivariable facets of not only fundamental aspects of photoswitch cooperativity, but also provides a pathway to modulate photophysics and electronics of multidimensional functional materials exhibiting thermo-photochromism.     

Spiropyran Photoswitches in the Context of DNA: Synthesis and Photochromic Properties

A new design is presented for the incorporation of spiropyran photoswitches into nucleic acids by oligonucleotide solid phase synthesis. This design enables interaction of the 6‐nitrospirobenzopyran (NitroBIPS) photoswitch with the adjacent nucleobases and leaves the photochemical properties of NitroBIPS intact. UV/Vis spectroscopy and HPLC revealed that NitroBIPS incorporated into DNA consists of up to 40 % merocyanine in its thermal equilibrium and undergoes reversible switching between the photoisomeric spiropyran (SP) and merocyanin (MC) state by alternating excitation using visible light or heat for at least fifteen switching cycles. Exchanging the chromene part of NitroBIPS on the DNA level gives access to differently substituted spiropyran derivatives allowing the screening for spiropyrans with suitable properties in a straightforward manner. Thus, by incorporating the highly hydrolysis‐stable pyrido‐spiropyran derivative PyBIPS pure light‐triggered reversible switching of a spiropyran in DNA has been realized for the first time. Therefore, this design represents a new useful platform for investigating the photochromic behavior of different spiropyran photoswitches in a nucleic acid environment and for using spiropyrans to induce light‐ or heat‐triggered changes in conformations or in fluorescence quenching properties of oligonucleotides.     

Control of the Structure and Functions of Biomaterials by Light

Vision and other light-triggered biochemical transformations in plants and living organisms represent a sophisticated biological processes in which optical signals are recorded and transduced as (physico)chemical events. Photoswitchable biomaterials are a new class of substances in which optical signals generate discrete “On” and “Off” states of biological functions, resembling logic gates that flip between 0 and 1 states in response to the changes in electric currents in computers. The (photo)chemistry of photochromic materials has been extensively developed in the past four decades. These materials isomerize reversibly upon light absorption, and the discrete photoisomeric states exhibit distinct spectral and chemical features. Integration of photoisomerizable (or photochromic) units into biomaterials allow their secondary functions such as biocatalysis, binding, and electron transfer to be tailored so that they can be switched on or off. This can be accomplished by chemical modification of the biomaterial by photoisomerizable units and by integration of biomaterials in photoisomerizable microenvironments such as monolayers or polymers. The photoswitchable properties of chemically modified biomaterials originate from the light-induced generation or perturbation of the biologically active site, whereas in photoisomerizable matrices they depend upon the regulation of the physical or chemical features of the photoisomerizable assemblies of polymers, monolayers, or membranes. Light-triggered activation of catalytic biomaterials provides a means of amplifying the recorded optical signal by biochemical transformations, and photostimulated biochemical redox switches allow its electrochemical transduction and amplification. The field of photoswitches based on biomaterials has developed extensively in the past few years within the general context of molecular switching devices and micromachinery. The extensive knowledge on the manipulation of biomaterials through genetic engineering and the fabrication of surfaces modified by biologically active materials enables us to prepare biomaterials with improved optical-switching features. Their application in optoelectronic or bioelectronic devices has been transformed from fantasy to reality. The use of photoswitchable biomaterials in information storage and processing devices (biocomputers), sensors, reversible immunosensors, and biological amplifiers of optical signals has already been demonstrated, but still leaves important future challenges.     

“Click-switch” – one-step conversion of organic azides into photochromic diarylethenes for the generation of light-controlled systems

Diarylethenes (DAEs) are an established class of photochromic molecules, but their effective incorporation into pre-existing targets is synthetically difficult. Here we describe a new class of DAEs in which one of the aryl rings is a 1,2,3-triazole that is formed by “click” chemistry between an azide on the target and a matching alkyne–cyclopentene–thiophene component. This late-stage zero-length linking allows for tight integration of the DAE with the target, thereby increasing the chances for photomodulation of target functions. Nineteen different DAEs were synthesized and their properties investigated. All showed photochromism. Electron-withdrawing groups, and in particular −M-substituents at the triazole and/or thiophene moiety resulted in DAEs with high photo- and thermostability. Further, the chemical nature of the cyclopentene bridge had a strong influence on the behaviour upon UV light irradiation. Incorporation of perfluorinated cyclopentene led to compounds with high photo- and thermostability, but the reversible photochromic reaction was restricted to halogenated solvents. Compounds containing the perhydrogenated cyclopentene bridge, on the other hand, allowed the reversible photochromic reaction in a wide range of solvents, but had on average lower photo- and thermostabilities. The combination of the perhydrocyclopentene bridge and electron-withdrawing groups resulted in a DAE with improved photostability and no solvent restriction. Quantum chemical calculations helped to identify the photoproducts formed in halogenated as well as non-halogenated solvents. For two optimized DAE photoswitches, photostationary state composition and reaction quantum yields were determined. These data revealed efficient photochemical ring closure and opening. We envision applications of these new photochromic diarylethenes in photonics, nanotechnology, photobiology, photopharmacology and materials science.

New photochromic diarylethenes are reported in which one aryl ring is a 1,2,3-triazole that is formed by “click” chemistry between an azide on the target and a matching alkyne–cyclopentene–thiophene component.     

Recent progress of luminescent metal complexes with photochromic units

Photo-responsive molecules have been studied extensively because of their light irradiation abilities that enable modulation of certain physical and chemical properties in emerging molecular electronic and photonic devices. For advanced photonic applications, photochromic metal complexes that have photochromic units as the photo-responsive ligand are highly desirable, as they allow improvement of the photochromic properties and their photo-switching functionality. This article focuses on recent progress in luminescent metal complexes with photochromic units. Luminescence-switching properties of photochromic metal complexes depend on characteristic electronic transitions. The electronic transitions of photochromic metal complexes can be divided into three categories: (1) π–π* transition of the ligand, (2) metal to ligand charge transfer (MLCT) in transition-metal complex, and (3) f–f transition in lanthanide complex. Luminescence modulation using various metal complexes with photochromic units has been studied extensively in recent years, and various applications for future molecular switching devices are expected in the field of advanced photonics. Based on the literature and our studies on luminescent metal complexes with photochromic units, we report on the recent progress of luminescent metal complexes with photochromic units.     

Synthesis of photochromic optically transparent polycarbonate glasses and study of their properties

Procedure was developed for surface dyeing of polycarbonate glass with photochromic thermally relaxing compounds from the classes of spiropyrans, spirooxazines, and chromenes via diffusion of photochromic molecules from solutions in cyclohexanone. It was shown that the highest diffusion efficiency of photochromic compounds without loss of the optical surface quality of polycarbonate glass is reached at a temperature of 80°C. Samples of photochromic polycarbonate glasses were obtained and their photochromic properties were studied.     

Thin film photochromic materials: Effect of the sol-gel ormosil matrix on the photochromic properties of naphthopyrans

Photochromic naphthopyran derivatives have been embedded in sol-gel prepared organically modified thin films. The introduction of organic functional groups into a silica matrix allows tailoring the surface of its pores and the polarity of the environment of the embedded host molecules. The photochromic properties of the naphthopyran molecules, such as the spectral properties of the coloured forms and the kinetics of the thermal bleaching, depend strongly on the polarity of the pores where the molecules are located and, hence, on the nature and loading of organic functional groups in the composition of the ormosil matrix. Important changes in the photochromic properties of the films have also been induced by modifications in the sol-gel preparation and processing parameters. The photostability of the photochromic molecules upon prolonged exposition to UV light is strongly related to the nature of the embedding ormosil matrix. The introduction of organic functional groups into the inner pore surface of the matrix, where the dye molecules will be located, affects the stability of the molecules, in terms of the effectiveness of the interaction between the photochromic molecules and the pore surface.     

Stiff-Stilbene Photoswitches: From Fundamental Studies to Emergent Applications

Stiff-stilbene, a sterically restricted fused ring analogue of stilbene, has been regularly used as a model compound in theoretical studies of stilbene photoisomerization. Lately, owing to its excellent photoswitching properties, it is increasingly being applied to reversibly control the properties and function of chemical as well as biological systems. Stiff-stilbene photoswitches possess a number of advantageous properties including a high quantum yield for photoisomerization and a high thermal stability. Furthermore, they undergo a large geometrical change upon isomerization and their synthesis is straightforward. Herein, we provide an overview of the basic properties of stiff-stilbene and of recent applications in supramolecular chemistry, catalysis, and biological systems.     

Push-Pull Stiff-Stilbene: Proton-Gated Visible-Light Photoswitching and Acid-Catalyzed Isomerization

Donor-acceptor substituted stiff-stilbene is shown to undergo isomerization induced by visible light avoiding the need for harmful UV light. This visible-light photoswitching is inhibited by protonation of the dimethylamino-donor unit, disrupting the push-pull character and thus, gating of the photochromic properties is allowed by acid/base addition. Remarkably, the addition of a mild acid also triggers fast thermal back-isomerization, which is unprecedented for stiff-stilbene photoswitches usually having a very high energy barrier for this process. These combined features offer unique orthogonal control over switching behavior by light and protonation, which is investigated in detail by ¹H NMR and UV/Vis spectroscopy. In addition, TD-DFT calculations are used to gain further insight into the absorption properties. Our results will help elevating the level of control over dynamic behavior in stiff-stilbene applications.     

Sulfur and Azobenzenes,a Profitable Liaison: Straightforward Synthesis of Photoswitchable Thioglycosides with Tunable Properties

Azobenzene photoswitches are valuable tools for controlling properties of molecular systems with light. We have been investigating azobenzene glycoconjugates to probe carbohydrate-protein interactions and to design glycoazobenzene macrocycles with chiroptical and physicochemical properties modulated by light irradiation. To date, direct conjugation of glycosides to azobenzenes was performed by reactions providing target compounds in limited yields. We therefore sought a more effective and reliable coupling method. In this paper, we report on a straightforward thioarylation of azobenzene derivatives with glycosyl thiols as well as other thiols, thereby increasing the scope of azobenzene conjugation. Even challenging unsymmetrical conjugates can be achieved in good yields via sequential or one-pot procedures. Importantly, red-shifted azoswitches, which are addressed with visible light, were easily functionalized. Additionally, by oxidation of the sulfide bridge to the respective sulfones, both the photochromic and the thermal relaxation properties of the core azobenzene can be tuned. Utilizing this option, we realized orthogonal three-state photoswitching in mixtures containing two distinct azobenzene thioglycosides.     

Recent developments in the field of metal complexes containing photochromic ligands: Modulation of linear and nonlinear optical properties

Organic photochromic molecules are important for the design of photoresponsive functional materials, as switches and memories. Over the past 10 years, research efforts have been directed towards the incorporation of photoresponsive molecules into metal systems, in order either to modulate the photochromic properties, or to photoregulate the redox, optical and magnetic properties of the organometallic moieties. This review article focuses on some of the recent work reported within the last few years in the area of organometallic and coordination complexes containing photochromic ligands for the photoregulation of optical and nonlinear optical properties. The first part is related to photochromic 1,2-diarylethene (DAE)-containing metal complexes, examples of mono- and multi-DAE metal-based will be discussed. The second part deals with metal complexes incorporating spiropyran and spirooxazine derivatives.     

General Principles for the Design of Visible-Light-Responsive Photoswitches: Tetra-ortho-Chloro-Azobenzenes

Molecular photoswitches enable reversible external control of biological systems, nanomachines, and smart materials. Their development is driven by the need for low energy (green-red-NIR) light switching, to allow non-invasive operation with deep tissue penetration. The lack of clear design principles for the adaptation and optimization of such systems limits further applications. Here we provide a design rulebook for tetra-ortho-chloroazobenzenes, an emerging class of visible-light-responsive photochromes, by elucidating the role that substituents play in defining their key characteristics: absorption spectra, band overlap, photoswitching efficiencies, and half-lives of the unstable cis isomers. This is achieved through joint photochemical and theoretical analyses of a representative library of molecules featuring substituents of varying electronic nature. A set of guidelines is presented that enables tuning of properties to the desired application through informed photochrome engineering.