Some Hybrid Systems of Chiral Schiff Base Zn(II) Complexes and Photochromic Spiropyrans for Environmental Ion Sensing

This is a review article including our recent results and some previous photo functional hybrid system having potential applications for environmental ion sensing. We have prepared several new and known chiral Schiff base Zn(II) complexes and measured (and also calculated) absorption and fluorescence spectra for sole complexes. After assembling hybrid systems with 1,3,3-trime- thylindolino-6’-nitrobenzopyrylospiran (SP) in methanol solutions, we measured spectral changes before and after alternate irradiation of UV and visible light. Intensity of fluorescence spectra for pale yellow Zn(II) complexes (λem = 450 nm, λex = 270 and 360 nm) was quenched by colorless SP (λem = 533 nm, λex = 612 nm). After UV light irradiation to form purple merocyanine (MC), photoisomerization resulted in changes of the intensity of absorption spectra as well as fluorescence spectra. Thus the hybrid systems could successfully act as molecular logic circuit by input (excitation by light) and output (intensity of fluorescence peaks). Moreover, we investigated concentration dependence of doped Zn(II) and Cu(II) ions to confirm quenching of intensity of fluorescence peaks by Zn(II) and Cu(II) MC complexes for metal ion sensing in solutions.

Learning from Spiropyrans:How to Make Further Developments of Donor-Acceptor Stenhouse Adducts

Donor-acceptor Stenhouse adducts(DASAs)as a species of novel photochromic molecules,have been developing rapidly and attracting broad researchers’sights since 2014.DASAs show visible/near-infrared(NIR)light induced linear-to-cyclic isomerization and heat induced cyclic-to-linear isomerization,therefore they are attractive in photoresponsive hydrogels,drug delivery,cell culturing and tissue engineering.As a series of well-known photoresponsive molecules,spiropyrans(SPs)show similar molecular properties and comparable photoswitching with DASAs.UV light triggers closed-to-open(also known as spirocyclic(SC)-to-merocyanine(MC))isomerization of SPs,while the reversed open-to-closed isomerization occurs under visible light or heat.Light irradiation switches the molecular color,scale,geometry,and polarity of SPs and DASAs reversibly.Since the researches on DASAs are still in the infancy,the chemical structures,isomerization mechanisms and potential applications need to be further investigated and explored.The well-studied SPs have important reference values to the comprehensive developments of DASAs.In the present review,we summarized,compared and discussed SPs and DASAs with regards to their molecular structures,synthesis,photoswitching and applications.We also make our perspective on the developments of DASA in future.

Synthesis of New Spiropyrans With a Polyaromatic or Heteroaromatic Pendant and Their Photochromic Behaviors

A series of spiropyrans with a polyaromatic or heteroaromatic pendant was synthesized conveniently. Their photochromic behaviors were investigated with the aid of absorption spectral measurements. The results indicated that the compounds with the same parent spiropyran but different aromatic pendant show significantly different photochromic properties. This may be due to the π-π orbital interaction between the polyaromatic pendant and the open photomerocyanine form of spiropyran. The results obtained are very useful in the molecule design area.

Spectral Properties and Photochromic Characteristics of Spiropyran Dyes

A bis-benzospiropyran（BBSP） and nitro-substituted indoline spirobenzopyrans（SBP） were prepared by following a simple procedure. The reaction mechanism of synthesizing bis-benzospiropyran is discussed. A comparative analysis of the spectral and photochromic properties between SBP and BBSP was carried out with the aid of a PMMA film. The results indicate that chemical structures and UV irradiation played an important role in the spectral and photochromic properties of SBP and BBSP, which would readily affect λmax of the colored forms and the reversibility. The IR spectra and ^1H NMR spectra of these compounds are used to interpret the photochromic phenomena under different UV irradiation and determine the configurations of SBP and BBSP.

Study on the Tautomerism of an Indoline Spiropyran in Compressed CO_2 and Ethanol Mixture

Thermodynamic and kinetic properties of the tautomerism of an indoline spiropyran in compressed CO2-ethanol mixture were studied by UV-Vis spectroscopy at 298.15 K, 303. 15 K, and 308.15 K. It was found that the composition of the mixture affects the equilibrium constant and the rate constant significantly.

Preparation of Photochromic Waterborne Polyurethane Films:Effect of Spiropyran Concentration on Photochromic Properties

Incorporation of photochromic compounds to the polymer through chemical bonding will result in an enhancement of photoactivity and stabilization of optical properties.Here,spiropyran(SP)was introduced into polyurethane(PU)through semi-continuous emulsion copolymerization to get waterborne polyurethane dispersion(SPU).Studies on photochromic properties by UV-vis technique demonstrated the absorption intensity increased with the increasing of SP concentration and the colorless film turned to purple under UV irradiation.The kinetics for ring-opening and ring-closing reaction against SP were both first order,but the rate constants decreased with the increasing of SP concentration.The prepared SPU films showed reasonable photostability and photoreversibility according to the convenient test methods under UV-vis irradiation.Temperature dependence studies demonstrated that the photobleaching rate increased at higher temperatures with the same SP concentration.The chemical combination between SP and isocyanate(NCO)end group of polyurethane was confirmed through swelling experiments.Morphology studies were conducted by scanning electron microscope(SEM)micrographs and showed good compatibility between SP and PU.

Synthesis and Crystal Structure of 4-(2-Methylene-1-ethyl-3,3-dimethylindoline-2'-yl)-6,8-dibromo-1'-ethyl-3',3'-dimethylspiro-[3,4-dihydro-2H-1-benzopyran-2,2'-indoline]

The title compound of 4-（2-methylene-1-ethyl-3,3-dimethylindoline-2＇-yl）-6,8-dibro-mo-1＇-ethyl-3＇,3＇-dimethylspiro[3,4-dihydro-2H-1-benzopyran-2,2＇-indoline],C33H36Br2N2O,as a dicondensed spiropyran（DC） has been synthesized by indoline in ethanol with 3,5-dibromo-salicyaldehyde.The compound was characterized by elemental analysis and IR spectra.Meanwhile,the crystal of the compound was obtained and determined by X-ray single-crystal diffraction.Crystal data：monoclinic system,space group P21/n,a=12.9699（15）,b=12.5196（13）,c=19.327（2）,β=106.493（3）°,Mr=636.46,V=3009.1（6） 3,Z=4,F（000）=1304,Dc=1.405 g/cm3,μ=2.722 mm-1,R=0.0554 and wR=0.1176 for 6892 independent reflections（Rint=0.0354） and 5699 observed reflections（Ⅰ〉 2σ（Ⅰ））.

Synthesis,Structure and Properties of a Novel Copolymer with Photochromic and Photoluminescence Functions

Photochromic and photoluminescence materials show bright colors under different excitation conditions,and thus,these functional materials have been applied in many fields.Based on the photochromic and photoluminescence theories,a block copolymer,which could be directly processed into nanofibers by electrospinning,was successfully prepared through atom transfer radical polymerization(ATRP).To synthesize the block copolymer,a vinyl monomer containing a spiropyran unit was employed to prepare the photochromic chain segment,and a polymethyl methacrylate(PMMA)chain segment was introduced to improve the processability of the block copolymer.Acting as the photoluminescence unit,the rare earth complex was linked to the side chain through coordination bonding between the rare earth ions and the ester groups of PMMA.When the photochromic and photoluminescence block copolymer was exposed to different wavelengths of ultraviolet(UV)light and visible(Vis)light,it could show white,red,green,yellow,and blue-purple.These results provide the potential of the as-prepared photochromic and photoluminescence block copolymer for application in fibers and fabrics.

PHOTOSWITCHABLE NANOFLUOROPHORES FOR INNOVATIVE BIOIMAGING

Photosensitive fluorescent probes have become powerful tools in chemical biology and molecular biophysics,which are used to investigate cellular processes with high temporal and spatial resolution.Accordingly,photosensitive fluorescent probes,including photoactivatable,photoconvertible,and photoswitchable fluorophores,have been extensively developed during the past decade.The photoswitchable fluorophores have received much attention because they highlight cellular events clearly.This minireview summarizes recent advances of using reversibly photoswitchable fluorophores and their applications in innovative bioimaging.Photoswitchable fluorophores include photoswitchable fluorescent proteins,photoswitchable fluorescent organic molecules(dyes),and photoswitchable fluorescent nanoparticles.Several strategies have been developed to synthesize photoswitchable fluorophores,including engineering combination proteins,chemical synthesis,polymerization,and self-assembly.Here we concentrate on polymer nanoparticles with optically switchable emission properties:either fluorescence on/offor dualalternating-color fluorescence photoswitching.The essential mechanisms of fluorescence photoswitching enable different types of photoswitchable fluorophores to change emission intensity or wavelength(color)and thus validating the basis of the fluorescence on/offor dual-color photoswitching design.Generally the possible applications of any fluorophores are to label biological targets,followed by specific imaging.The newly developed photoswitchable fluorophores enable super-resolution fluorescence imaging because of their photosensitive emission.Finally,we summarize the important area regarding future research and development on photoswitchable fluorescent nanoparticles.

基于碳点功能化的二氧化硅封装螺吡喃的光响应材料用于动态信息加密

开发刺激响应荧光材料对于解决信息安全的新兴需求至关重要.本文中,我们提出了一种刺激响应双发射荧光材料SP@SiO_(2)-CDs(SP:螺吡喃),该材料是通过将螺吡喃化合物封装到碳点功能化的二氧化硅中得到的.这种复合材料显示碳点在470 nm处发射蓝色光,螺吡喃在620 nm处发射红色光.在连续紫外光(365 nm)照射下,螺吡喃分子经历从闭环到开环的过程,SiO_(2)-CDs和异构部花青之间可以实现显著的荧光能量共振转移.SP@SiO_(2)-CDs复合物粉末不仅可以在紫外光刺激下光致变色从黄色到粉色,而且可以实现从淡蓝色到橙红色的双发射荧光转换.当暴露在白光下时,这种动态荧光行为可以完全恢复到初始状态.基于荧光的时间依赖性,本文成功开发了动态防伪图案和多重编码.此外,通过掺杂聚二甲基硅氧烷,获得了具有高柔韧性和机械强度的薄膜,并展示了其在高级信息加密中的应用.该工作为提高离线便携式信息加密的安全性提供了一种新方法.

The guest CH_(3)CN molecule triggers solid-state photochromism in a Cu_(2)I_(2)-based MOF for advanced time-dependent encryption and inkless erasable printing

It remains a big challenge to develop solid-state stimuli-responsive materials for time-dependent information encryption and inkless erasable printing with long retention times.Herein,a 2D Cu_(2)I_(2)-based MOF with photoresponsive spiropyran(SP)groups orderly installed on its skeleton is developed.The structural isomerization from SP to colored merocyanine(MC)form can be triggered by removing the CH_(3)CN guests.Besides,the degree of structural isomerization and the retention time can be adjusted by controlling the amount of CH_(3)CN guests,exhibiting dynamic photochromic behavior with multicolor states and tunable retention time.Based on these advantages,time-dependent information encryption is successfully achieved.Furthermore,the long retention time(>72 h)of the MC form under daylight conditions in the CH_(3)CN-removed Cu_(2)I_(2)-based MOF and good repeatability make it promising in various applications,such as temporary calendars,price-cards,billboards,and reusable identity cards.This work provides a novel design strategy to fabricate multi-functional MOF-based smart materials for challenging applications of time-dependent information encryption and inkless erasable printing.

Spiropyran isomerization triggering ESIPT for visualization of pH fluctuations during oxidative stress in living cells

Intracellular pH homeostasis is foundation of maintaining normal physiological functions.More and more evidences show that intracellular pH fluctuations were usually associated with many diseases(such as cancer,epilepsy and neurodegenerative diseases).It is very important to develop in situ real-time determination of pH.In recent years,it has been verified that pH can regulate the isomerization process of spiropyran.Thus,we report a pH fluorescent probe BSL,which is a closed loop spiropyran structure by coupling benzothiazole derivatives with indole salts.We utilizes the process of spiropyran isomerization as the trigger of excited state intramolecular proton transfer(ESIPT)effect,and adjust the process of spiropyran isomerization through pH,and then the molecular transformation from enol to ketone(enol:525 nm,ketone:677 nm)through the ESIPT effect.This process achieved accurate measurement of pH.The probe BSL showed sensitive and reversible fluorescence response to pH in vitro.Ultimately,BSL was successfully applied to detect pH fluctuations in cell oxidative stress model.

Visible light responsive spiropyran derivatives based on dynamic coordination bonds

Spiropyrans(SPs) are a well-known class of photochromic compounds and have found widespread application due to their unique properties. However, for many conventional SPs, high energy ultraviolet(UV)light is commonly essential to drive photoisomerization, leading to poor fatigue resistance. Moreover, the practical application of spiropyrans is hindered by their fast fading speed due to the instability of closed forms(SP) or open forms(MC). Herein, we disclose a novel strategy to address these challenges through introducing both electron-donating substituents to stabilize the SP and dynamic coordination bonds to stabilize the MC. The resulting new spiropyrans complexes exhibit negative photochromic properties, with fast visible light response, good stability of both SP and MC, and significantly improved fatigue resistance.

Two-photon photopolymerization directly initiated by spiropyran photochromic molecules

Here,we report the ability of spiropyrans to initiate two-photon polymerization(TPP)for the first time in the literature.The comparison and synergies between the spiropyran photochromic molecule of interest,namely 6-nitro-BIPS,and well-known photoinitiators of radical photopolymerization have been studied.The spiropyran(SPy)molecule can initiate TPP in the presence of trifunctional acrylic monomers and create true 3D structures.The comparison with Irgacure 819,a well-known Type-I photoinitiator,shows that SPy has a comparable capability for TPP.In addition,the combination of SPy with methyl diethanolamine increased the reactivity of both one-and two-photon polymerizations.In the last section,we discuss which SPy isomer is the active photochromic species capable of generating radicals for initiating two-photon polymerization.

Synthesis of novel chalcone derivatives and their stabilization effect of spiropyran in PMMA films

Three novel bis-chalcone derivatives with different alkyldioxy spacers were synthesized and dispersed into polymethyl methacrylate （PMMA） chloroform solution with 6-nitro-1＇-ethyl-3＇,3＇-dimethylspiro-2H-1-benzopyran-2,U-indoline （ESP） to prepare photochromic PMMA films in a facile way. After irradiation with 365 nm UV light, the photocrosslinking reaction between chalcone units was proved to retard the decolorization of merocyanine form of the photochromic spiropyran effectively, as results of the steric hindrance produced by photocycloaddition of chalcone groups. It has been found that the bis-chalcone molecule with the shortest spacer has the most effective stabilizing effect on retardation of decoloration of spiropyran. reserved.

A Multiresponsive Hydrophobic Associating Hydrogel Based on Azobenzene and Spiropyran

Summary of main observation and conclusion Stimuli-responsive hydrogels crosslinked by weak noncovalent bonds such as hydrogen bonds,ionic interactions,host-guest interactions and hydrophobic interactions have been extensively investigated.Herein,azobenzene and spiropyran acting as two hydrophobic pendant groups were introduced into a hydrophilic polyacrylamide (PAM) via free radical copolymerization to construct a hydrophobic interaction based thermo-,light-responsive polymer hydrogel.Its viscosity and color could be reversibly regulated by heating and cooling.Meanwhile,its color could be specifically switched by light without obvious viscosity change.The gel was also capable of being transited to sol by addition of β-cyclodextrin (β-CD),which encaged the hydrophobic groups and then increased the solubility of polymer in water.The hydrogel could be regained after UV irradiation at λ=365 nm,and after irradiation at λ=440 nm,the hydrogel changed into a clear sol again.

A fluorescent probe based on a spiropyran for sensitive detection of Ce^3+ ion

A spiropyran-based probe was developed.It serves as a fluorescence turn-on probe for selective detection of Ce^3+in both ethanol and aqueous(water/ethanol,1:9 or 9:1,v/v)media.Ce3+can induce photochromism of the probe though the probe exhibits negligible photochromic property by itself.The probe is sensitive to Ce3+and the detection limit reaches 1.7μmol/L.It exhibits a high selectivity for Ce^3+ion over other common metal cations including Li^+,Na^+,Ag^+,Sr^2+,Ni^2+,Co^2+,Hg^2+,Zn^2+,Cr^3+,Al^3+,Fe^3+and Bi^3+and lanthanide ions Nd^3+,Yb^3+and La^3+.The probe may be used for quantitative determination of the concentration of Ce3+ion in a range of 1-10μmol/L and for application to environmental water samples.Sensing mechanism of the probe towards Ce3+ion is proposed.

Mechanically controlled FRET to achieve high-contrast fluorescence switching

Organic luminescent materials with the ability to reversibly switch the luminescence when subjected to external stimuli have attracted considerable interest in recent years. However, luminescent materials with mechanochromic and photochromic dualresponsive properties are rarely reported. Hererin, we designed and synthesized a molecule P1 with dipeptide as a spacer to link rhodamine B and spiropyran moieties. P1 exhibited efficient photochromic properties both in solution and solid state. Highcontrast independent fluorescence switch was also realized under the stimulus of external force. Moreover, two-step ring opening reaction and subsequent fluorescence resonance energy transfer process between the donor-acceptor pairs within one single molecule achieved successive color switch by mechanical control. Therefore, this behavior of P1 made it a promising candidate for high-contrast and sensitive optical recording and mechanical sensing system.

Structure and photochromism of spiropyran assemblies

Nanocluster assemblies of spiropyran compounds have been prepared by means of LB technique, and the relations between the subphase, pH value, condition of preparation and the structure of the fabricated LB film are systematically investigated. The stability, photochromic fatigue properties of the spiropyran LB film, which are of primary importance in optic signal storage applications, are also studied in detail. A kind of supermolecular film with homogeneously distributed J aggregates of similar granular size has been obtained with the optical resolution in the order of micrometer. Finally, a nondestructive readout method for such an LB film to be used as the optic signal storage film is proposed.