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.     

Efficient One‐step Synthesis and Properties of Photochromic Diarylethenes Having an Indene Bridging Unit

Two novel isomeric photochromic diarylethenes with an indene bridging unit have been prepared by a simple and efficient one‐step synthesis method. Their properties, including photochromic behavior, fluorescent properties and fatigue resistance, have been investigated. These two isomeric compounds showed photochromic back‐and‐forth reactions with ultraviolet and visible light both in solution and in PMMA film. Their ring‐open forms exhibited appreciable fluorescence, which was quenched by the ring‐closed forms. All results indicated that diarylethenes derivatives with indene‐aryl bridges exhibited rather high fatigue resistance and good thermally irreversible photochromic properties.     

Photochromic Spiropyran Dendrimers: ‘Click’ Syntheses,Characterization, and Optical Properties

Resorting to ‘click chemistry’, four photochromic dendrimers, A‐Tri‐SP, B‐Tri‐SP, C‐Tri‐SP, and D‐Hex‐SP, have been synthesized facilely in sound yields of 85, 88, 94, and 80%, respectively. These dendrimers have been obtained by the straightforward coupling of azido‐attached photochromic spiropyran units to acetylenic‐terminated dendritic cores. The photochromic dendrimers show typical photochromic properties both in tetrahydrofuran solution and in poly(methyl methacrylate) film. They are demonstrated to be endowed with superior performance in comparison to the corresponding spiropyran monomer in terms of larger optical density, better stability of the open ring form, higher sensitivity towards the coordination of ferric ions, and better two‐photon absorption properties.

     

一种新光致变色二芳基乙烯化合物的合成、光致变色反应动力学、荧光和结构研究

The photochromic diarylethene, 1,2-bis[2-methyl-5-（3-trifluoromethylphenyl）-3-thienyl]perfluorocyclopentene （BMTTP）, was synthesized and its photochromic kinetics, fluorescence and X-ray structure were investigated. This compound underwent a photochromic reaction both in solution and the single crystalline phase. Its cyclization/cycloreversion process was determined to be zeroth/first order reaction, respectively, and this is the first report on the cyclization/cycloreversion reaction order. In addition, its fluorescence property was also discussed.     

Optical switching,photophysical, and electrochemical behaviors of pendant triazole‐linked indolylfulgimide polymer

Triazole‐linked 2‐indolylfulgimide polymer has been synthesized and its photochromic switching behavior has been characterized by NMR, IR, GPC, TGA, DSC, and UV–Vis spectroscopy. The synthesized photochromic polymer showed absorption peak maxima at 386 and 510 nm wherein the absorption at 510 nm was attributed to charge transfer from triazole ring nitrogen to carbonyl carbon of fulgimide unit. Fluorescence lifetime studies on exciting at 550 nm reveals triexponential behavior with fluorescence decay around 0.1, 1 and 4.2 ns, which correspond to open (E), closed (C) form of fulgimide and triazole ring, respectively. Whereas exciting at 470 nm evidences biexponential fit with fluorescence decay around 0.1 and 2.2 ns, which corresponds to the closed (C) form and triazole ring, respectively. Fluorescence decay of triazole ring was found to be influenced by the excitation wavelength. The cyclic voltammogram of open form of polymer depicts irreversible reductive wave at ?1.4 V. On illumination with 360‐nm light, the reduction wave of polymer was shifted toward less cathodic wave at ?0.9 V; this leads to formation of the closed form of fulgimide unit. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Novel Bisthienylethene Containing Ferrocenyl‐Substituted Naphthalimide: A Photo‐ and Redox Multi‐Addressable Molecular Switch

A new photochromic bisthienylethene system (BTE? NAFc) is reported in which the ferrocene unit (Fc) is incorporated into a naphthalimide chromophore as the central ethene bridging unit. The incorporated Fc unit in the photochromic system of BTE? NAFc has several effects on optical properties, such as fluorescence‐modulation through photoinduced electron transfer (PET), a decrease in the photochromic cyclization quantum yield, and a selective two‐step oxidation process. The ability to drive ring‐opening and ring‐closing reactions with a secondary redox‐modulation provides increased functionality to the photochromic system. Based on these meaningful photo‐ and redox‐modulation properties, five unprecedented multi‐addressable states (BTE? NAFc, BTE? NAFc⁺, c‐BTE? NAFc, c‐BTE? NAFc⁺, and BTE⁺? NAFc⁺) and gated photochromism are successfully obtained within the unimolecular BTE platform, thus providing deeper insight into photochromic systems as multifunctional outputs.     

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.     

Synthesis and characterization of soluble polyimides derived from 2,2′‐Bis(3,4‐dicarboxyphenoxy)‐9,9′‐spirobifluorene dianhydride

The synthesis of aromatic poly(ether imide)s containing spirobifluorene units in the polymer backbone is described. 2,2′‐Bis(3,4‐dicarboxyphenoxy)‐9,9′‐spirobifluorene dianhydride, which was used as a new monomer, was synthesized with 2,2′‐dihydroxy‐9,9′‐spirobifluorene as the starting material. In the spiro‐segment, the rings of the connected bifluorene were orthogonally arranged. This bis(ether anhydride) monomer was employed in reactions with a variety of aromatic diamines to furnish poly(ether imide)s, involving an initial ring‐opening polycondensation and subsequent chemically induced cyclodehydration. Excellent solubility in common organic solvents at room temperature, good optical transparency, and high thermal stability are the prominent characteristic features of these new polymers, which can be attributed to the presence of spiro‐fused orthogonal bifluorene segments along the polymer chain. The glass‐transition temperatures of the polyimides were 240–293 °C, and the 5% weight‐loss temperatures were greater than 500 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 262–268, 2002     

具有多个光致变色单元的二芳基乙烯分子光密度的增加

3,4-Diaryl-2,5-dihydropyrrole with multiphotochromophore units la was synthesized and its photochromic properties were investigated. It showed that all photochromophore units underwent reversible ring-opening （1a） and ring-closing （1b） photoisomerization reactions in both solution and polymer film with UV/Vis light irradiation, and photochromic properties of la were similar to those of photochromic diarylethene with monophotochromophore 2a. It was found that the optical density of lb was increased linearly with increase of the photochromophore units by comparison with that of 2b in the same condition. It was also found that no significant changes in absorption band and response time between diarylethenes with multiphotochromophores and monophotochromophore were detected in the same condition.     

Synthesis,Characterization and Photochromic Properties of Novel Naphthopyrans with Hydrazone Unit Residue

A series of naphthopyrans with hydrazone unit ( 8a – 8m ), were synthesized and characterized by ¹H NMR, ¹³C NMR, IR and HRMS. The photochromic properties were investigated under continuous irradiation, in particular regard to the fatigue resistance and the lifetime of the colored open form in solution and polymers. The results showed that these compounds had both good photochromic properties and high fatigue resistance. Detailed studies showed that representative compound 8d (3,3‐di‐4‐methoxybenzoic acid methylenehydrazino‐[3H]‐naphtho [2,1‐b]pyran) had good photochromic properties in THF solution, in solid state, and in polymers, and exhibited a significant bathochromic shift in the spectra of the open forms compared to known naphthopyrans 9 (3,3‐diphenyl‐[3H]‐naphtho[2,1‐b]pyran). On the other hand, the higher melting points of target compounds are promising for the polymer film preparation through hot‐melt method.     

The effect of addition of fluorescent moieties to dihydropyrenes: enhancing photochromicity and fluorescence monitoring

A series of dihydropyrenes with appending fluorescent moieties were synthesized with the objective of increasing the photochromic efficiency for this class of compounds and to establish how suitable fluorescence would be to follow their photochromic behavior. The ring opening quantum yields of dihydropyrenes with aroyl substituents at the 4-position showed increased ring opening quantum yields without a decrease of the half-life for the thermal reversion of the less stable open isomer, the metacyclophanediene to the dihydropyrene. The fluorescence of the appending naphthoyl or pyrenoyl moieties was not suitable to follow the photochromic cycling of the dihydropyrenes. However, the emission detected above 600 nm of the closed isomer of the dihydropyrene moiety was shown to be a good monitoring method for the photochromic cycling.     

Ring transformations of heterocyclic compounds. XXIII. The UV irradiation product of photochromic 2,4,6‐triaryl‐1‐(spiro[2H‐l‐benzopyran‐2,2′‐indoline]‐6‐yl)pyridinium salts ‐ A phenolate betaine or a pyridinium substituted merocyanine dye?

The synthesis of the novel 2,4,6‐triaryl‐1‐(spiro[2H‐1‐benzopyran‐2,2′‐indoline]‐6‐yl)pyridiniumper‐chlorates 4 by reaction of 5 ‐nitrosalicylaldehydes 6 with 1,3,3‐trimethyl‐2‐methyleneindoline ( 7 ) to 6‐nitro‐spiro[2H‐1‐benzopyran‐2,2′‐indolines] 1 , their stannous chloride reduction to the 6‐amino derivatives 8 , followed by a 2,6‐[C₅+N] ring transformation with 2,4,6‐triarylpyrylium perchlorates 9 , is reported. UV irradiation experiments in twenty solvents of different polarity prove their photochromic properties and show that the photochemically generated negative solvatochromic dyes 5 , formed by ring opening of the benzopyran moiety of 4 , are rather merocyanine than pyridinium phenolate betaine dyes.     

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.     

Two‐Photon Excitation of a Plasmonic Nanoswitch Monitored by Single‐Molecule Fluorescence Microscopy

Visible‐light excitation of the surface plasmon band of silver nanoplates can effectively localize and concentrate the incident electromagnetic field enhancing the photochemical performance of organic molecules. Herein, the first single‐molecule study of the plasmon‐assisted isomerization of a photochrome‐fluorophore dyad, designed to switch between a nonfluorescent and a fluorescent state in response to the photochromic transformation, is reported. The photochemistry of the switchable assembly, consisting of a photochromic benzooxazine chemically conjugated to a coumarin moiety, is examined in real time with total internal reflection fluorescence microscopy in the presence of silver nanoplates excited with a 633 nm laser. The metallic nanostructures significantly enhance the visible light‐induced performance of the photoconversion, which normally requires ultraviolet excitation. The resulting ring‐open isomer is strongly fluorescent and can also be excited at 633 nm. These stochastic emission events are used to monitor photochromic activation and show quadratic dependence on incident power. The utilization of a single laser wavelength for both photochromic activation and excitation effectively mimics a pseudo two‐colours system.     

Electrochemistry and electrogenerated chemiluminescence of 3,6-di(spirobifluorene)-N-phenylcarbazole

We report here the electrochemistry, luminescence, and electrogenerated chemiluminescence (ECL) of 3,6-dispirobifluorene-N-phenylcarbazole (DSBFNPC). DSBFNPC contains two spirobifluorene groups covalently attached to the N-phenylcarbazole core. The optimized geometry as determined from semiempirical MNDO calculations shows that the phenyl group is twisted 89 degrees from the plane of central carbazole, indicating a lack of electron delocalization between these groups. However, the two fluorene rings of each spirobifluorene group are twisted 58 degrees relative to each other and two spirobifluorene groups are twisted 64 degrees from the N-phenylcarbazole ring, suggesting some charge delocalization among these groups. The cyclic voltammetry of this compound shows two reversible oxidation waves (assigned to the formation of the cation and dication) and a two-electron reduction wave that becomes reversible at higher scan rates (assigned to formation of anion). Digital simulations were carried out to obtain details of the electrochemical processes, and electrochemical behavior was compared to that of phenylcarbazole (PC). Upon cycling between the oxidation and reduction waves, ECL is produced by radical ion annihilation. The photophysical properties of DSBFNPC show a strong resemblance to the parent compound, PC, and the ECL spectrum produced via radical ion annihilation shows good agreement with the fluorescence emission spectrum of DSBFNPC.     

A High‐Content Diarylethene Photochromic Polymer for an Efficient Fluorescence Modulation

Summary: A highly fluorescent photochromic polymer, poly‐BTFO4, was prepared. The fluorescence quantum yield of the poly‐BTFO4 was six times higher than that of BTFO4. Fatigue resistance of the polymer at its photostationary state was significantly enhanced compared with that of BTFO4. Importantly, the poly‐BTFO4 film also showed an efficient photochromism as well as strong fluorescence similar to the results in solution, which allow photoinduced fluorescence switching applicable to optical switches.

Improvement of fluorescence quantum yield and fatigue resistance.     

DFT/TDDFT Investigation of the Modulation of Photochromic Properties in an Organoboron‐Based Diarylethene by Fluoride Ions

The diarylethene derivative 1,2‐bis‐(5′‐dimesitylboryl‐2′‐methylthieny‐3′‐yl)‐cyclopentene ( 1 ) containing dimesitylboryl groups is an interesting photochromic material. The dimesitylboryl groups can bind to F^?, which tunes the optical and electronic properties of the diarylethene compound. Hence, the diarylethene derivative 1 containing dimesitylboryl groups is sensitive to both light and F^?, and its photochromic properties can be tuned by a fluoride ion. Herein, we studied the substituent effect of dimesitylboron groups on the optical properties of both the closed‐ring and open‐ring isomers of the diarylethene molecule by DFT/TDDFT calculations and found that these methods are reliable for the determination of the lowest singlet excitation energies of diarylethene compounds. The introduction of dimesitylboron groups to the diarylethene compound can elongate its conjugation length and change the excited‐state properties from π→π* transition to a charge‐transfer state. This explains the modulation of photochromic properties through the introduction of dimesitylboron groups. Furthermore, the photochromic properties can be tuned through the binding of F^? to a boron center and the excited state of the diarylethene compound is changed from a charge‐transfer state to a π→π* transition. Hence, a subtle control of the photochromic spectroscopic properties was realized. In addition, the changes of electronic characteristics by the isomerization reaction of diarylethene compounds were also investigated with theoretical calculations. For the model compound 2 without dimesitylboryl groups, the closed‐ring isomer has better hole‐ and electron‐injection abilities, as well as higher charge‐transport rates, than the open‐ring isomer. The introduction of dimesitylboron groups to diarylethene can dramatically improve the charge‐injection and ‐transport abilities. The closed isomer of compound 1 ( 1 C ) has the best hole‐ and electron‐injection abilities, whereas the charge‐transport rates of the open isomer of compound 1 ( 1 O ) are higher than those of 1 C . Importantly, 1 O is an electron‐accepting and ‐transport material. These results show that the diarylethene compound containing dimesitylboryl groups has promising potential to be applied in optoelectronic devices and thus is worth to be further investigated.     

Synthesis of a highly luminescent three-dimensional pyrene dye based on the spirobifluorene skeleton

We have synthesized a highly luminescent (log e > 5.0, F > 0.9) pyrene dye based on a spirobifluorene skeleton [2,2',7,7'-tetrakis(7-tert-butyl-1-pyrenyl)-9,9'-spirobi[9H-fluorene; 4-PySBF]. The use of spirobifluorene prevents fluorescence quenching by intramolecular energy transfer and/or electron transfer among the chromophores in the excited state. The emission spectra of 4-PySBF exhibited a red shift of 20 nm in comparison to a model compound [9,9'-dioctyl-2,7-bis(7-tert-butyl-1-pyrenyl)-9H-fluorene; 2-PyF], but its UV-Vis spectrum remained unchanged.     

A Versatile Synthesis,PM3‐Semiempirical,Antibacterial, and Antitumor Evaluation of Some Bioactive Pyrazoles

This research work describes the synthesis and biological properties of some novel isolated or fused heterocyclic ring systems with pyrazole, for example; enaminones containing pyrazolone ring photochromic functional unit, 4‐[(4‐chlorophenylamino)methylene]‐3‐methyl‐1‐phenyl‐1H‐pyrazol‐5(4H)‐one (3) and some analogous derivatives 4, 9, and 10, also as pyrazolo[3,4‐b]pyridine, pyrazolo[3,4‐b]quinoline, pyrazolo[3′,4′:4,5]thieno[2,3‐c]pyrazoline and pyrazolo[3,4‐c]pyrazole were synthesized and characterized. Newly synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, mass spectral data and quantum mechanical calculations. Selected products were tested for their antibacterial and antitumor agents.     

Efficient upconversion fluorescence in a blue-emitting spirobifluorene-anthracene copolymer doped with low concentrations of Pt(II)octaethylporphyrin

Upconversion-induced fluorescence in platinum-octaethylporphyrin (PtOEP)-doped thin films of a spirobifluorene-anthracene copolymer has been investigated. Upon exciting in the range of the absorption band (2.31 eV, 537 nm) of the guest molecules, blue fluorescence (2.75 eV, 450 nm) from the spirobifluorene host was observed. The intensity of the upconverted emission was found to be one order of magnitude higher than from a PtOEP doped but anthracene-free spirobifluorene copolymer and than previously reported for metallated porphyrin-doped polyfluorene samples. It is argued that the efficient upconversion originates from the triplet energy transfer from the phosphorescent dopant to the sensitive unit of the host polymer, followed by triplet-triplet annihilation and finally blue emission from the spirobifluorene host polymer backbone.