二芳基乙烯类化合物用作光开关的最新研究

本文在综述二芳基乙烯类化合物各种性能的基础上,重点介绍了二芳基乙烯类化合物作为荧光光控开关、荧光共振能量转移、光致变色电开关、光致变色磁开关、光致变色液晶开关和多功能光致变色开关的最新发展动态,以及二芳基乙烯类化合物的形态对光开关性能的影响。最后对未来光存储材料的研究趋势作了展望。     

Giant Amplification of Photoswitching by a Few Photons in Fluorescent Photochromic Organic Nanoparticles

Controlling or switching the optical signal from a large collection of molecules with the minimum of photons represents an extremely attractive concept. Promising fundamental and practical applications may be derived from such a photon‐saving principle. With this aim in mind, we have prepared fluorescent photochromic organic nanoparticles (NPs), showing bright red emission, complete ON–OFF contrast with full reversibility, and excellent fatigue resistance. Most interestingly, upon successive UV and visible light irradiation, the NPs exhibit a complete fluorescence quenching and recovery at very low photochromic conversion levels (<5 %), leading to the fluorescence photoswitching of 420±20 molecules for only one converted photochromic molecule. This “giant amplification of fluorescence photoswitching” originates from efficient intermolecular energy‐transfer processes within the NPs.     

Two‐Photon Photochromism of a Diarylethene Enhanced by Förster Resonance Energy Transfer from Two‐Photon Absorbing Fluorenes

Resonance energy transfer from two-photon absorbing fluorene derivatives to the photochromic compound 3,4-bis-(2,4,5-trimethyl-thiophen-3-yl)furan-2,5-dione (PC 1) is investigated in hexane under one- and two-photon excitation. The quenching of the steady-state fluorescence of donor molecules in the presence of the diarylethene acceptor is used to study the nature of resonance energy transfer. The F?rster distances and critical acceptor concentrations are determined for nonbound donor-acceptor pairs in homogeneous molecular ensembles. Quite significantly, up to a two-fold enhancement in the velocity of the photochromic transformation of 1, in the presence of two-photon absorbing fluorene derivatives, is demonstrated.     

亲水性二芳基乙烯荧光分子开关的研究进展

二芳基乙烯荧光分子开关因具有优良的抗疲劳性和双稳态特征而被广泛地研究与应用,亲水化成为其作为荧光开关探针走向应用的关键点之一。本文综述了亲水性二芳基乙烯荧光分子开关当前的研究进展,归纳了实现亲水性的几种重要途径和结构,分析了各种亲水化方法的优缺点,并着重介绍了亲水性二芳基乙烯荧光分子开关作为荧光开关探针在化学传感、生物传感、生物成像以及超分辨成像等领域的应用现状,并指出当前应用研究中存在的一些问题,同时也对其未来的应用前景进行了展望。     

A photochromic acceptor as a reversible light-driven switch in fluorescence resonance energy transfer (FRET)

A method has been developed for the quantitative determination of fluorescence resonance energy transfer (FRET) based on the modulation of donor fluorescence upon the reversible photoconversion of a photochromic acceptor. A model system was devised, consisting of Lucifer Yellow cadaverine (LYC, donor) conjugated to the photochromic molecule, 6-nitroBIPS (1′,3′-dihydro-1′-(2-carboxyethyl)-3′,3′-dimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-(2H)-indoline]). Near-ultraviolet irradiation catalyzes the conversion of the colorless spiropyran (SP) to the colored merocyanine (MC) form of 6-nitroBIPS. Only the MC form absorbs at the emission wavelengths of the donor, thereby potentiating FRET, as demonstrated by quenching of the donor. Subsequent irradiation in the visible MC absorption band reverts 6-nitroBIPS to the SP form and FRET is inactivated. The acceptor exhibited high photostability under repeated cycles of alternating UV–Vis irradiation. In this model system, the intramolecular FRET efficiency was close to 100%. The observed maximal donor quenching of 34±3% was indicative of an equilibrium determined by the high quantum efficiency of forward conversion (SP→MC) induced by near-UV irradiation and a low but finite quantum efficiency of the back reaction resulting from excitation of the MC form directly as well as indirectly (by FRET via the donor). A quantitative formalism for the photokinetic scheme was developed. Photochromic FRET (pcFRET) permits repeated, quantitative, and non-destructive FRET determinations for arbitrary relative concentrations of donor and acceptor and thus offers great potential for monitoring dynamic molecular interactions in living cells over extended observation times by fluorescence microscopy.     

Digital photoswitching of fluorescence based on the photochromism of diarylethene derivatives at a single-molecule level

Photochromic reactions of diarylethene derivatives were detected at a single-molecule level by using a fluorescence technique. Fluorescent photoswitching molecules in which photochromic diarylethene and fluorescent bis(phenylethynyl)anthracene units are linked through an adamantyl spacer were synthesized, and switching of fluorescence upon irradiation with UV and visible light was followed in solution as well as on polymer films at the single-molecule level. Although in solution the fluorescence intensity gradually changed upon irradiation with UV and visible light, digital on/off switching between two discrete states was observed at the single-molecule level. The "on"- and "off"-times were dependent on the power of UV and visible light. When the power of UV and visible light was increased, the average on- and off-times became short in proportion to the reciprocal power of the light. The response-times were found to show distribution. The distribution of the on- and off-times is considered to reflect the difference in the micro-environment as well as conformation of the molecules.     

Photocontrolled Intramolecular Charge/Energy Transfer and Fluorescence Switching of Tetraphenylethene‐Dithienylethene‐Perylenemonoimide Triad with Donor–Bridge–Acceptor Structure

Photochromic 1,2‐dithienylethene (DTE) derivatives with a high thermal stability and fatigue resistance are appealing for optical switching of fluorescence. Here, we introduce a donor–photochromic bridge–acceptor tetraphenylethene‐dithienylethene‐perylenemonoimide (TPE‐DTE‐PMI) triad, in which TPE acts as the electron donor, PMI as the electron acceptor, and DTE as the photochromic bridge. In this system, the localized and intramolecular charge transfer emission of TPE‐DTE‐PMI with various Stokes shifts have been observed due to the photoinduced intramolecular charge transfer in different solvents. Upon UV irradiation, the fluorescence quenching resulting from photochromic fluorescence resonance energy transfer in TPE‐DTE‐PMI has been demonstrated in solution and in solid films. The fluorescence on/off switching ratio in polymethylacrylate film exceeds 100, a value much higher than in polymethylmethacrylate film, thus indicating that the fluorescence switching is dependent on matrices.     

Energy transfer and fluorescence quenching in complexes of polymethine dyes with human serum albumin

Electronic excitation energy transfer (EET) between molecules of polymethine dyes bound to human serum albumin (HSA) has been established and studied by absorption and fluorescence spectroscopy as well as by fluorescence decay measurements. In this system, excitation of the donor dye molecule leads to fluorescence of the acceptor dye molecule, both bound to HSA, with donor fluorescence quenching by the acceptor. The short distance between the donor and the acceptor (25-28 A) revealed from the Forster model of EET as well as some spectroscopic data show that both molecules are probably located in the same binding domain of HSA. The role of HSA is to bring donor and acceptor molecules together to a distance adequate to achieve EET as well as to increase the donor and acceptor fluorescence quantum yields. Efficient quenching of the intrinsic HSA fluorescence by some polymethine dyes (oxonols) is observed. The experimental results fit well a model for the formation of a weakly fluorescent dye-HSA complex; the quencher in this complex should be located in the immediate vicinity of the HSA fluorophore group (Trp(214)).     

A photochromic fluorescent switch in an organogel system with non-destructive readout ability

A fluorescent organogel based on photochromic dithienylethene was obtained, whose optimal excitation wavelength (470 nm) results in little structural change of both open and closed isomers of diarylethene, thus presenting the first example of a fluorescent switch with non-destructive readout ability in the gel state.     

A Combination of Selective Light Reflection and Fluorescence Modulation in a Cholesteric Polymer Matrix

Summary: The phase behavior and optical properties of a cholesteric ternary copolymer, containing nematogenic phenylbenzoate, cholesteric, and photochromic diarylethene side groups, and its mixture with 2 wt.‐% fluorescent dopant were studied. The investigation of the kinetics of a photochemical opening‐cycle process of the photochromic groups in the cholesteric mixture proved the energy transfer from the fluorescent dopant to the photochromic diarylethene groups. It was shown that the fluorescence intensity of the fluorescent dopant could be controlled by the portion of the “closed” form of the diarylethene groups. During the photocyclization of the photochromic groups a “degeneration” of the selective light reflection of the cholesteric matrix is observed.

Fluorescence‐resonance energy transfer makes possible the process of photosensitization of the back ring‐opening photoreaction of the photochromic diarylethene groups in the cholesteric polymer matrix.     

Diheteroarylethenes as thermally stable photoswitchable acceptors in photochromic fluorescence resonance energy transfer (pcFRET)

We have employed diheteroarylethenes as acceptors for photochromic FRET (pcFRET), a technique introduced for the quantitative determination of fluorescence resonance energy transfer (FRET). In pcFRET, the fluorescent emission of the donor is modulated by cyclical transformations of a photochromic acceptor. Light induces a reversible change in the structure and, concomitantly, in the absorption properties of the acceptor. Only the closed forms of the selected diheteroarylethenes 2a and 2b have an absorption band overlapping the emission band of the donor, 1. The corresponding variation in the overlap integral (and thus critical transfer distance R(o)) between the two states provides the means for reversibly switching the process of FRET on and off, allowing direct and repeated evaluation of the relative changes in the donor fluorescence quantum yield. The diheteroarylethenes demonstrate excellent stability in aqueous media, an absence of thermal back reactions, and negligible fatigue. The equilibration of these systems after exposure to near-UV or visible light follows simple monoexponential kinetics. We developed a general conceptual scheme for such coupled photochromic-FRET reactions, allowing quantitative interpretations of the photostationary and kinetic data, from which the quantum yields for the cyclization and cycloreversion reactions of the photochromic acceptor were calculated.     

Switchable three-state fluorescence of a nonconjugated donor-acceptor triarylborane

A nonconjugated fluorescent molecule with a triarylboron acceptor and an alkylamine donor has been found to display bright green fluorescence due to charge transfer through space, which can be reversibly deactivated by blocking either the donor or acceptor site. Binding of the fluoride ion to boron switches the fluorescence color to sky blue, while protonation of the amine with acid switches the emission color to the purple fluorescence of the acceptor chromophore.     

Nondestructive Photoluminescence Read‐Out by Intramolecular Electron Transfer in a Perylene Bisimide‐Diarylethene Dyad

A novel, highly stable photochromic dyad 3 based on a perylene bisimide (PBI) fluorophore and a diarylethene (DAE) photochrome was synthesized and the optical and photophysical properties of this dyad were studied in detail by steady‐state and time‐resolved ultrafast spectroscopy. This photochromic dyad can be switched reversibly by UV‐light irradiation of its ring‐open form 3 o leading to the ring‐closed form 3 c , and back reaction of 3 c to 3 o by irradiation with visible light. Solvent‐dependent fluorescence studies revealed that the emission of ring‐closed form 3 c is drastically quenched in solvents of medium (e.g., chloroform) to high (e.g., acetone) polarities, while the emission of the ring‐open form 3 o is appreciably quenched only in highly polar solvents like DMF. The strong fluorescence quenching of 3 c is attributed to a photoinduced electron‐transfer (PET) process from the excited PBI unit to ring‐closed DAE moiety, as this process is thermodynamically highly favorable with a Gibbs free energy value of ?0.34 eV in dichloromethane. The electron‐transfer mechanism for the fluorescence quenching of ring‐closed 3 c is substantiated by ultrafast transient measurements in dichloromethane and acetone, revealing stabilization of charge‐separated states of 3 c in these solvents. Our results reported here show that the new photochromic dyad 3 has potential for nondestructive read‐out in write/read/erase fluorescent memory systems.     

Diarylethene doped biocompatible polymer dots for fluorescence switching

The photochromic molecule diarylethene works as a "toggle switch" for biocompatible fluorescence polymer dots and enables fluorescence switching in biological samples.     

Fluorescent sensors for organophosphorus nerve agent mimics

We present a small molecule sensor that provides an optical response to the presence of an organophosphorus (OP)-containing nerve agent mimic. The design contains three key features: a primary alcohol, a tertiary amine in close proximity to the alcohol, and a fluorescent group used as the optical readout. In the sensor's rest state, the lone pair of electrons of the basic amine quenches the fluorescence of the nearby fluorophore through photoinduced electron transfer (PET). Exposure to an OP nerve agent mimic triggers phosphorylation of the primary alcohol followed rapidly by an intramolecular substitution reaction as the amine displaces the created phosphate. The quaternized ammonium salt produced by this cyclization reaction no longer possesses a lone pair of electrons, and a fluorescence readout is observed as the nonradiative PET quenching pathway of the fluorophore is shut down.     

Photochromism of a diarylethene charge-transfer complex: photochemical control of intermolecular charge-transfer interaction

A diarylethene derivative bearing a phenylenediamine group formed radical ions with an electron acceptor molecule in solution, and the concentration of the radical ions was modulated by the photochromic reaction of the diarylethene, reflecting the difference in the electron-donating character between the open- and closed-ring isomers.     

Influence of the environment on photoinduced electron transfer: comparison between organized monolayers at the air-water interface and monolayer assemblies on glass

Photoinduced electron transfer (PET) has been investigated in organized monolayers at the air-water interface and in monolayer assemblies on glass in an effort to evaluate the influence of solvent reorganization and molecular dynamics on PET. The donor monolayer contained an amphiphilic thiacyanine dye, and the electron acceptors were methyl viologen and dioctadecyl viologen, respectively. The distance dependence is described here by a hard disk model, where an acceptor molecule within a disk with a radius rDA around the excited donor molecule quenches the donor fluorescence due to electron transfer. Acceptor molecules outside the disk are considered ineffective. The critical radius rDA is larger in monolayer assemblies on glass (rDA = 1.97 nm) than at the air-water interface (rDA = 1.15 nm) as evaluated from steady-state fluorescence quenching. This large difference indicates that the time between thermal collisions generating and destroying the energetic match required for electron tunneling from the excited donor molecule to the acceptor is quite different in the two systems that are compared.     

Flexibility of the aldolase molecule measured using quenching-induced variations of the Forster distance for fluorescence energy transfer

The range of flexibility of the rabbit muscle aldolase molecule was studied using fluorescent labelled aldolase. The protein molecule was specifically labelled on the opposite sites of the enzyme subunit with the fluorescence energy donor and acceptor residues. Labelled aldolase with full enzymatic activity was used as a tool in the FRET studies between IAEDANS — donor or Cys-289 and IAF — acceptor on Cys-239. A range of Forster distance (R) was obtained by collisional quenching of the donor emission. The experiments of donor fluorescence quenching with wide range of acrylamide concentrations have shown the changes of donor-acceptor distances. In the absence of quencher the D-A distance distribution in characterized by an average value of 40.4 ?, and a half-width of 0.13 ?. A dramatic increase in half-width to 17.7? is observed after expositions of the enzyme to high acrylamide concentrations (0.13 M-0.68 M).     

A fluorescent photochromic compound for labeling biomolecules

A fluorescent photochromic compound, composed of diarylethene, fluorescein and succinimidyl ester units, was developed for the controllable fluorescent labeling of biomolecules based on a small molecule.     

Quenching of singlets and triplets by reversible ionization followed by charge recombination

The reversible electron transfer from donor to excited molecule (acceptor of electron) is shown to be the irreversible energy quenching, if it is completed by subsequent irreversible recombination radical-ions which are produced. The Stern-Volmer constant of fluorescence as well as the Markovian rate constant of triplet quenching are calculated analytically, assuming the electron transfer is contact. The multiple Rehm-Weller effect is shown to be peculiar to both constants.