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.

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.

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.

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.

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.

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.

Utilization of a spiropyran derivative in a polymeric film optode for selective fluorescent sensing of zinc ion

A new spiropyran derivative was synthesized and first utilized in a polymeric film-based optical sensor for zinc ion. Spiropyrans, combining the characteristics of metal binding and signal transduction, show potential function in the design of optical chemical sensors (optodes) toward metal ions. When embedded in a plasticized poly (vinyl chloride) (PVC) membrane, the newly synthesized spiropyran derivative 1 exhibits obvious fluorescence enhancement at 630 nm in the presence of zinc ion in aqueous solution. With the optimum condition described, the optode membrane responds to zinc ion over a dynamic range of 4.94×10?7 to 4.15×10?4 mol·L?1, with a detection limit of 1.51×10?7 mol·L?1. The membrane not only displays excellent photostability, reproducibility and reversibility, but also exhibits high selectivity toward zinc ion over transition metal ions including Hg2+, Cd2+, Pb2+, Cu2+, Fe3+and common cationic ions presented in the physiological fluids.

In situ Observation of the Photochromism in the Langmuir Monolayer of a Non-typical Amphiphilic Spiropyran Derivative at the Air/Water Interface

In situ photochromic process in the monolayer of a photochromic spiropyran derivative without long alkyl chain, was investigated. The photochromism at the air/water interface under different surface pressures was studied by surface pressure area isotherms, surface pressure time curves, area time curves and Brewster angle microscopy. Both forms of the compound were found to form monolayers at the air/water interface although it does not have long alkyl chain. A large area expansion in the monolayer corresponding to a zero th order reaction was found at the initial stage of the UV light irradiation. A series of dynamic investigations revealed that at high pressure after phase transition in the monolayer, the surface pressure changes greatly under alternative irradiation of UV and visible light. An obvious morphological change accompanying with the photochromism was observed in situ .

Dual sensitivity of spiropyran-functionalized carbon dots for full color conversions

Multicolor phosphors that respond rapidly to external stimuli are highly desirable for many applications, including lighting,optical displays and sensors. Herein, spiropyran(SP)-functionalized carbon dots(CDs) were synthesized with a broad-spectrum output that were responsive to both ultraviolet(UV)/visible light and pH. The SP-CDs possessed strong ester linkages between the UV-absorbing/blue-emitting CDs and blue-absorbing/red-emitting surface SP groups, allowing efficient F?rster resonance energy transfer(FRET) between the donor and acceptor. UV irradiation or acid addition cause the SP ring opening to merocyanine(MC) or protonated MCH+forms, respectively, together with the formation of sheet-like aggregates. These processes enhanced the red emissions by the SP groups and attenuated blue emissions from the CDs. These changes were fully reversible under visible light or basic conditions, respectively, allowing dynamic regulation of the fluorescence properties(emission colors from blue to red, photoluminescence(PL) intensity) under photoirradiation on the timescale of minutes. As proof-of concept, we demonstrate that the emission properties of the SP-CDs can be used to construct UV and pH sensing materials as well as light emitting diode(LED) with different colors.

A semiclassical molecular dynamics of the photochromic ring-opening reaction of spiropyran

The photochromic ring-opening reaction of spiropyran（SP） has been investigated by a realistic semiclassical dynamics simulation,accompanied by SA3-CASSCF（12 10）/MS-CASPT2 potential energy curves（PECs） of S0–S2.The main simulation results show the dominate pathway corresponds to the ringopening process of trans-SP to form the most stable merocyanine（MC） product.These findings provide more important complementarity for interpreting experimental observations.

UV-induced self-assembly of the inclusion complexes formed between a long-chain photochromic spiropyran and cyclodextrins

Photochromic spiropyran with a long chain alkyl substitute can form axial complexes with α-, β-, and γ-cyclodextrin, respectively. The complexes show normal photochromism. The novel property of the colored forms of the inclusion complexes is that they can assemble into dimers at relatively low concentration or J-aggregates at relatively high concentration. For α-, β-, and γ-cyclodextrin, λmax of the J-aggregates appear at 700 650, and 630 nm, respectively. The sizes of the cavities of cyclodextrins have very little effect on the spectra and decoloration kinetics of the dimers, but have great effects on the spectra of the J-aggregates. Unlike the charge transfer complex of Krongauz, the decoloration process of the dimers or J-aggregates cannot be described by an exponential or a two-exponential kinetics, but obey half-order kinetics very well. Another result that can be deduced from the kinetic analysis is that unlike the dimers formed in apolar solvents or in polymers, which consist of a

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.

Dual-Responsive Thermally Activated Delayed Fluorescence of Spiropyran Derivatives

For the first time,a series of photochromic dyes SP1-3 with dual-responsive thermally activated delayed fluorescence(TADF)characteristics were reported in this research.Benefitting from the reversible light-responsive property of SP1-3,the eigen TADF of these compounds could be regulated between 588 and 678 nm or turned on/off by different wavelengths of light irradiation in a polyvinylpyrrolidone(PVP)matrix.The emission lifetime of the spiropyran derivative was prolonged to millisecond level for the first time.Moreover,the delayed fluorescence of SP1 and SP3 could also be manipulated by mechanical force because of the mechanochromistic properties of SP1 and SP3.This research is a significant breakthrough for photochromic materials and may broaden its scope.