Photochromic Groups Research Articles

In Situ Control of Photochromic Behavior through Dual Photo-Isomerization Using Cobaloxime Complexes with Salicylidene-3-aminopyridine and 3-Cyanopropyl Ligands

In situ control of crystalline-state photochromism was achieved using a photo-isomerization reaction of cobaloxime complexes. These dual photoreactive complexes that have the photochromic salicylideneaniline ligand and 3-cyanopropyl group as the axial alkyl group were synthesized and crystallographically characterized. When each crystal was exposed to visible light, the 3-cyanopropyl group isomerized to a 1-cyanopropyl group while retaining the single crystal form. Although both 3-cyanopropyl and 1-cyanopropyl group complex crystals showed the yellow (or orange) to orange (or light brown) photochromism upon UV light irradiation, the fading rate of the photochromic color was significantly changed after the 3–1 isomerization. The differences in fading rates can be rationalized by a change of the volume of the cavity around the carbon–nitrogen bonds of the three salicylideneaniline derivatives, which is caused by the 3–1 photo-isomerization in the crystal. Also, the reactivity of 3–1 photo-isomerization was explained by the cavity around the 3-cyanopropyl group.

Optical Behaviors of Cholesteric Liquid-Crystalline Polyester Composites with Various Chiral Photochromic Dopants.

New developments in the field of chiral nematic liquid crystals, such as color displays, are now being widely proposed. This article describes the tunable incident reflection band based on composite materials of low-molecular-weight chiroptical dopants and polymeric networks. These materials have advantages including easily manageable color according to a change in the helical pitch of the cholesteric liquid crystal upon exposure to light. A series of novel chiral dopants of isosorbide derivatives containing photochromic groups and three new main-chain liquid crystalline polyesters were synthesized and identified using nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and elemental analyses. The phase-transition temperatures and the liquid-crystal phase determination of the synthesized polymers were estimated using DSC, WAXD, and POM analyses. The influence of the dopant concentrations and the solubility in a liquid crystalline polymer blend were also studied. The reflection band of the cholesteric liquid crystalline composites could be adjusted and tuned with a wide range of color variation across the entire visible region. A real image recording of the chiral photochromic liquid crystalline polymer blend was achieved by exposing it to UV light through a mask.

Electrochemical and spectrophotometric properties of polymers based on derivatives of di- and triphenylamines as promising materials for electronic applications

Novel phenylamine-substituted derivatives, possessing different photochromic groups, were investigated. The electrochemical activity of the monomers and polymers were studied by usage of the electrochemical and spectroelectrochemical measurements. Heterocyclic side rings influence on the oxidation potential of monomers, decreasing its value below oxidation potential in comparison to parent phenylamine units. The removal of electron is easier for diphenylamine derivatives than for the triphenylamine ones. Electroactivity of monomers allows to polymerize them into macromolecule chains. Triphenylamine-based polymers are more stable as a result of the enlarged conjugated systems. Furthermore, the energy gap value of the final polymer can be reduced by introduction of additional branch into the monomer structure.

Photoisomerisation in Aminoazobenzene-Substituted Ruthenium(II) Tris(bipyridine) Complexes: Influence of the Conjugation Pathway.

Transition-metal complexes containing stimuli-responsive systems are attractive for applications in optical devices, photonic memory, photosensing, as well as luminescence imaging. Amongst them, photochromic metal complexes offer the possibility of combining the specific properties of the metal centre and the optical response of the photochromic group. The synthesis, the electrochemical properties and the photophysical characterisation of a series of donor-acceptor azobenzene derivatives that possess bipyridine groups connected to a 4-dialkylaminoazobenzene moiety through various linkers are presented. DFT and TD-DFT calculations were performed to complement the experimental findings and contribute to their interpretation. The position and nature of the linker (ethynyl, triazolyl, none) were engineered and shown to induce different electronic coupling between donor and acceptor in ligands and complexes. This in turn led to strong modulations in terms of photoisomerisation of the ligands and complexes.

Photoswitchable semiconductor nanocrystals with self-regulating photochromic Förster resonance energy transfer acceptors.

Photoswitchable molecules and nanoparticles constitute superior biosensors for a wide range of industrial, research and biomedical applications. Rendered reversible by spontaneous or deterministic means, such probes facilitate many of the techniques in fluorescence microscopy that surpass the optical resolution dictated by diffraction. Here we have devised a family of photoswitchable quantum dots (psQDs) in which the semiconductor core functions as a fluorescence donor in Förster resonance energy transfer (FRET), and multiple photochromic diheteroarylethene groups function as acceptors upon activation by ultraviolet light. The QDs were coated with a polymer bearing photochromic groups attached via linkers of different length. Despite the resulting nominal differences in donor-acceptor separation and anticipated FRET efficiencies, the maximum quenching of all psQD preparations was 38±2%. This result was attributable to the large ultraviolet absorption cross-section of the QDs, leading to preferential cycloreversion of photochromic groups situated closer to the nanoparticle surface and/or with a more favourable orientation.

Light-responsive polymer surfaces via postpolymerization modification of grafted polymer-brush structures.

Light-induced, spatially well-defined, reversible switching of surface properties enables the creation of remote-controlled smart surfaces. We have taken advantage of the unique high-resolution structuring capabilities of extreme ultraviolet (EUV) interference lithography to produce nanostructured photoresponsive polymer brushes. Patterns of poly(glycidyl methacrylate) (PGMA) and poly(methacrylic acid) (PMAA) were grafted from two different 100 μm thick fluoropolymer substrates by means of a radiation-initiated, grafting-from approach based on free-radical polymerization (FRP). Photochromic properties were introduced via novel one- or two-step postpolymerization modifications with spiropyran (SP) derivatives, which allowed us to control the number of photochromic groups on the polymer brushes. Depending on the degree of functionalization and the local chemical environment, the SP moieties can open upon UV-light exposure to form zwitterionic, deeply colored, and fluorescent merocyanines (MCs) and reclose to the colorless SP configuration via thermal or visible light-induced relaxation. Switching kinetics were studied by means of time-resolved fluorescence microscopy and compared with kinetic measurements of the SP moiety in solution. The results indicated the importance, for the intensity of the switching, of the local chemical environment provided by both the polymer brush and added solvents, and showed the predominant influence on the ring-closing kinetics of polar solvents, which stabilize the MC form. To allow further characterization of the polymer-brush arrangements on a macroscopic scale, similar, but unstructured brush systems were grafted from fluoropolymers after large-area activation using EUV radiation or argon plasma. All steps of the postpolymerization modification were characterized in detail using attenuated total reflection infrared (ATR-IR) spectroscopy. Furthermore, a light-induced reversible static-contact-angle switch with a range of up to 15° for PGMA-SP brushes and up to 30° for PMA-SP brushes was demonstrated upon alternating UV- and visible-light irradiation.

Liquid-crystalline polymer systems: From the past to the present

In the first part of this review, in a brief historical perspective, we consider the evolution of the scientific activity of Nikolai Al’fredovich Plate, Academician of the Russian Academy of Sciences: from grafted polymer systems to comb-shaped and liquid-crystalline polymers. The main biographical data on Plate are related to his scientific work at Moscow State University, and his research-development strategy to create and study of LC polymers with comb-shaped structure is considered. The second part of the article is devoted to discussion of scientific directions in this area that were developed in the last five years at the Laboratory of Chemical Transformations of Polymers, where Plate started his scientific activity. Special attention is paid to the research data on photochromic liquid-crystal polymers and composites. A concept of the preparation of multifunctional comb-shaped LC polymers containing mesogenic, photochromic, and chiral groups, as well as functional (crown ether) fragments, is presented. The photo-orientational processes occurring in photochromic LC polymers, which were used to prepare “command” surfaces and photo-orientators, are considered in detail. The preparation of a new class of photochromic polyamides with azobenzene, cinnamoyl and coumarin groups, which have been proposed for the obtaining of polymer films with latent data recording, is described. The phase behaviors and photo-optical properties of synthesized photochromic triple LC block copolymers are reported. Examples of holograms based on cholesteric LC blends, which allow double recording on the same polymer film, are presented. The results of investigations of light-controlled cholesteric polymer-stabilized LC networks with crown ether fragments in the compositions of macromolecules that are able to form complexes with metal ions are presented. The methods of preparation of photocontrolled and electrically controlled polymer LC nanocomposites with nanoparticles, as well as research data on their photo-optical properties, are considered.

Photochemical characterization of bi-functional compounds containing indolinospiropyran and chalcone groups

Two bi-functional compounds with a structure containing both a photochromic group indolinospiropyran and a photo-crosslinkable group chalcone connected by a soft spacer chain with alkyloxy and alkyl ester, or alkyldiester groups, were synthesized and the structures were confirmed with 1H NMR, FTIR, and UV–Vis spectroscopy. The bi-functional compounds were dissolved in polymethyl methacrylate (PMMA) or PMMA-co-4-hydroxychalcone methacrylate chloroform solution, and used to prepare photochromic PMMA films by a facile spin-coating method. Photocrosslinking reaction between the chalcone groups and photochromism of the spiropyran groups were accompanied under irradiation of 365 nm UV light. It was proved that the chalcone derivatives containing polymer films effectively retarded the decaying behavior of photochromism after photocycloaddition of the chalcone groups.

Photochromic Properties of Polyoxotungstates with Grafted Spiropyran Molecules

The first systems associating in a single molecule polyoxotungstates (POTs) and photochromic organic groups have been elaborated. Using the (TBA)4[PW11O39{Sn(C6H4I)}] precursor, two hybrid organic-inorganic species where a spiropyran derivative (SP) has been covalently grafted onto a {PW11Sn} fragment via a Sonogashira coupling have been successfully obtained. Alternatively, a complex containing a silicotungstate {PW11Si2} unit connected to two spiropyran entities has been characterized. The purity of these species has been assessed using several techniques, including (1)H and (31)P NMR spectroscopy, mass spectrometry, and electrochemical measurements. The optical properties of the hybrid materials have been investigated both in solution and in the solid state. These studies reveal that the grafting of SPs onto POTs does not significantly alter the photochromic behavior of the organic chromophore in solution. In contrast, these novel hybrid SP-POT materials display highly effective solid-state photochromism from neutral SP molecules initially nonphotochromic in the crystalline state. The photoresponses of the SP-POT systems in the solid state strongly depend on the nature and the number of grafted SP groups.

Quantum Dots as Templates for Self-Assembly of Photoswitchable Polymers: Small, Dual-Color Nanoparticles Capable of Facile Photomodulation

A photomodulatable amphiphilic polymer has been synthesized with a backbone of poly[isobutylene-alt-maleic anhydride] and pendant dodecyl alkyl chains, Lucifer Yellow (LY) fluorescent probes, and diheteroarylethenes photochromic (PC) groups. The latter serve as reversible UV-activated FRET acceptors for the LY donors. We characterized the spectral and switching properties of the polymer in an organic solvent (CHCl(3)). In an aqueous medium the polymer forms polymersomes, constituting fluorescence probes ~75 nm in diameter. Self-assembly of the polymer on the surface of a quantum dot (QD) serving as a template creates a dual-color photoswitchable nanoparticle (psNP) with improved properties due to the increase in polymer density and efficiency of PC photoconversion. The psNP exhibits a second QD red emission band that functions as an internal standard requiring only a single excitation wavelength, and is much reduced in size (<20 nm diameter) compared to the polymersomes. The QD template also greatly increases the depth of modulation by photochromic FRET of the LY emission monitored by both steady-state and time-resolved (lifetime) fluorescence (from 20%→70%, and from 12%→55%, respectively).

Photomagnetic Studies of Spin‐Crossover‐ and Photochromic‐Based Complexes

AbstractThis work reports on the combination between photochromic complexes (Na2[Fe(CN)5(NO)]·2H2O and K2[RuCl5(NO)]) with spin‐crossover compounds derived from FeIII complexes {[Fe(qsal)2]+ and [Fe(salEen)2]+; Hqsal = N‐(8‐quinolyl)salicylaldimine; HsalEen = N‐[(2‐ethylamino)ethyl]salicylaldimine}. These associations have resulted in the synthesis of new materials that contain a spin‐crossover unit and a photochromic unit, as evidenced by their X‐ray structure. Spectroscopic, magnetic and photomagnetic properties of these complexes were studied, with or without light irradiation, to evaluate the possible influence of the photochromic group on the spin transition. [Fe(qsal)2]2[Fe(CN)5(NO)]·solvent, [Fe(salEen)2]2[Fe(CN)5(NO)] and [Fe(qsal)2]2[Ru(CN)5(NO)]·2.5H2O all exhibit a spin transition. The light‐induced excited spin‐state trapping (LIESST) effect was detected in the (Fe‐qsal)‐based complexes. [Fe(qsal)2]2[Ru(CN)5(NO)]·2.5H2O also exhibits a reverse‐LIESST effect. Regardless of the complex, no photochromic effect from the nitroprusside units was detected.

Thermo- and photoresponsive reversible changes in localized surface plasmon resonance of gold nanoparticles covered by poly(N-isopropylacrylamide) with photochromic diarylethene end group

Abstract Thermoresponsive poly( N -isopropylacrylamide) (poly(NIPAm)) with a diarylethene (DE) chromophore at the end group (DE–poly(NIPAm)) was synthesized by reversible addition-fragmentation chain transfer polymerization. The resulting polymer has a lower critical solution temperature at 33 °C and exhibits photochromism in water upon photoirradiation. Gold nanoparticles covered with DE–poly(NIPAm) were prepared by malate reduction, followed by the addition of DE–poly(NIPAm) with SH at the ω-end group. The localized surface plasmon resonance band of the gold nanoparticles exhibits a bathochromic shift with heating and photoirradiation. This is ascribed to changes in the refractive index by the shrunken dehydrated state and the photochromic reaction of the DE chromophore with heating and photoirradiation, respectively.

Polarised light-induced orientation and reorientation processes and unexpected ‘memory effect’ in side-chain azobenzene-containing LC polymers

Photoorientation phenomena in thin films of side-chain azobenzene-containing polymethacrylates having different length of spacer (4, 6 and 10 methylene units) were studied in detail. Irradiation of these films with polarised blue light (473 nm) leads to photoorientation of photochromic side groups in a direction perpendicular to the polarisation plane of the incident light. It was shown that values of photoinduced dichroism increase with the lengthening of the methylene spacer. Annealing of the polymers films at a temperature higher than glass transition results in an additional growth of dichroism. However, the degree of uniaxial order of the annealed films was almost the same. The reorientation phenomena in irradiated and annealed films were studied by the irradiation of these films with the light of the same wavelength (473 nm) but polarisation rotated by 90° with respect to the first irradiation cycle. A study of the kinetics of the reorientation showed that the polymers with a spacer having four and six methylenic groups undergo the fast complete reorientation, whereas the polymer with 10 methylenic units is characterised by a much slower reorientation process. Moreover, an unusual ‘memory effect’ was found for the polymer films deposited on quartz substrates; annealing of the films after reorientation restores an initial orientation state achieved by the first irradiation cycle, whereas the films spin-coated on mica surface do not demonstrate this phenomenon. The ‘memory effect’ is probably associated with the roughness of the quartz substrates.

Synthesis and Properties of a Novel Photochromic Diarylethene Bearing Methyl Group

A new unsymmetrical photochromic diarylethene 1-(2,4-dimethyl-3-isoxazol)-2-[2-methyl-5-(2-methyl)-3-thienyl]perfluorocyclopentene (1a) has been synthesized. Its photochromic properties in solution and PMMA film were investigated. Diarylethene 1a changed the color from colorless to pink upon irradiation with 297 nm UV light, in which absorption maxima were observed at 518 nm in hexane and at 527 nm in PMMA film, respectively. In hexane solution, the open-ring isomer of the diarylethene 1 exhibited relatively fluorescence at 386 nm when excited at 309 nm.

A fluorescence switch based on a controllable photochromic naphthopyran group

A fluorescence switch based on photoisomerization of naphthopyran (NP) has been designed by employing 2-(pyridin-2-yl)-benzimidazole (BPI) and the naphthopyran containing two pyran rings (NP) as fluorescent dye and photochromic compound, respectively. The fluorescence switch of benzimidazole derivative can be modulated either by controlling the irradiation time of UV light or by adjusting the amount ratio of fluorescent benzimidazole derivative to photochromic naphthopyran in both solution and polymethyl methacrylate (PMMA) film. The experimental results indicated that the decrease of fluorescence intensity of benzimidazole derivative is attributed to the interaction of benzimidazole with naphthopyran.

Effect of Molecular Structure and Thermal Treatment on Photo‐optical Properties of Photochromic Azobenzene‐containing Polymer Films

AbstractThree novel photochromic azobenzene‐containing comb‐shaped polyacrylates are synthesized and their phase behavior and photo‐optical properties are studied. The influence of the side photochromic group structure, thermal treatment, and light irradiation on aggregation of azobenzene chromophores in thin spin‐coated films of the polymers is investigated in detail. Special attention is paid to studying the photo‐orientation processes in polymers films induced by polarized blue light (473 nm). The relationship between the photochromic group architecture, phase behavior, thermal treatment of films, and kinetics of chromophore photo‐orientation is established and discussed. It is found that the position of the NN bond in chromophores plays an important role in the kinetics of the process, but does not affect the maximum value of dichroism. magnified image

Comparison of photochromic, yellow, and clear intraocular lenses in human eyes under photopic and mesopic lighting conditions

To evaluate the results of the first blue light-filtering photochromic intraocular lens (IOL) and compare them with those of a regular yellow blue light-filtering IOL and a clear ultraviolet-filtering IOL in human eyes under various lighting conditions. Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University; Beijing Ophthalmology & Visual Sciences Key Laboratory, Beijing, China. Prospective comparative clinical study. This study evaluated eyes that had implantation of 1 of the following 3 IOLs: photochromic Aurium Matrix acrylic, model 400; yellow AF-1 (UY); or clear MC611MI. All eyes were followed for 3 months. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities, contrast vision (lighting 400 lux, 30 lux, 5 lux), contrast sensitivity, color vision (Farnsworth-Munsell 100-hue test under 400 lux, 30 lux), and patient questionnaire responses were evaluated. The photochromic IOL group comprised 39 eyes; the yellow IOL group, 41 eyes; and the clear IOL group, 38 eyes. There were no significant differences between the 3 IOLs in UDVA, CDVA, contrast sensitivity, or questionnaire responses. The photochromic group had significantly better color vision than the yellow IOL group at 30 lux and better contrast vision at 5% contrast (P < .05); however, there were no significant differences between the photochromic IOL group and the clear IOL group (P > .05). The photochromic blue light-filtering IOL performed as well as the yellow and clear IOLs under photopic conditions. Under mesopic conditions, the yellow IOL gave poor color vision and contrast sensitivity.

Bridging the Visible: The Modulation of the Absorption by More than 450 nm

The coexistence of 18 isomers, identified by NMR spectroscopy and gathered into six states with very different absorption properties, is observed upon irradiation with selective wavelengths of a triphotochromic system joining two naphthopyran entities through a dithienylethene bridge. The sequential electronic coupling of photochromic groups resulted in an absorption behavior reaching far into NIR.

Conformational Switching of G‐Quadruplex DNA by Photoregulation

Native, self-assembling nucleic acid nanomachines that can walk, move, or rotate have been developed. Owing to their ability to form diverse secondary structures, for example, by the highly sequence-specific hybridization of complementary sequences, the hybridization of DNA and RNA through Watson–Crick H bonds, and the assembly of triplexes through Hoogsteen bonds, nucleic acids are ideal building blocks for the construction of nanodevices. Quadruplex architecture is a nucleic acid secondary structure that plays an important role in nanomachine research, particularly in the control of reversible folding and extension of the G quadruplex of DNA in the presence of external stimuli. Mergny and coworkers reported that a copper(II)-mediated structural switch with a flexible ligand could regulate the conformation of the G quadruplex. Nanodevices based on a quadruplex-toduplex-transition that rely on the use of single-stranded DNA as fuels have been shown to perform rotary movements. Among external stimuli, such as temperature, pH value, electrical-field strength, and molecular recognition, photoregulation is particularly advantageous for controlling movement and conformation. For example, photoregulation does not require any additional components and does not cause undesirable side reactions. Irradiation is an accurate and simple method, and the timing, location, and strength of light can be controlled readily. Moreover, photoregulation provides a clean source of energy and can be repeated many times without loss of efficiency. The introduction of a photochromic group into biomolecules, such as peptides, oligonucleotides, sugar scaffolds, and phospholipids, can cause conformational changes that alter the photochemical properties of the biomolecule. Accordingly, various biological processes involving modified biomolecules can be regulated in a straightforward manner by irradiation. Recently, Ogasawara and Maeda demonstrated the successful photoregulation of G-quadruplex formation through isomerization of a photochromic nucleobase, G, incorporated in aptamers. Spada and co-workers introduced a photoactive moiety at the C8 position of a lipophilic guanosine derivative to regulate the existence of G quartets. However, all these photocontrollers are photochromic modified nucleobases. Specific molecules have not been shown to function as G-quadruplex photocontrollers; thus, we became interested in designing a photoswitch to regulate the formation of G-quadruplex DNA. The azobenzene moiety is widely used as a photoresponsive molecular tool because it possesses excellent photochemical characteristics. Specifically, azobenzene isomerizes to predominantly trans and cis forms under visible (Vis) and ultraviolet (UV) light, respectively. In this study, we synthesized the azobenzene derivative 1 (Scheme 1) to control the movement and conformation of a G quadruplex by irradiation. Our results suggest that the formation and dissociation of G-quadruplex DNAwas induced by interconversion of the trans and cis forms of compound 1. Compound 1 was synthesized by treating 4,4’-dihydroxyazobenzene with 1-(2-chloroethyl)piperidine hydrochloride

Liquid-crystalline polymers: Past, present, and future

The main steps of the evolution in studies related to the design and investigation of the structure and properties of thermotropic LC polymers containing mesogenic groups are discussed. The principal attention is focused on the results of experiments performed at the Laboratory of Chemical Transformations of Polymers, Faculty of Chemistry, Moscow State University, which was established and guided by Academician N.A. Plate from 1966 to 1985 and then supervised by V.P. Shibaev, the author of this review. Historical evidence is presented to demonstrate the contribution of Russian scientists to the development of approaches to the synthesis and study of chiral and electro- and photocontrollable comb-shaped LC polymers and related composites. The concept of preparing multifunctional LC copolymers and LC networks containing mesogenic, chiral, photochromic, and functional (including ionophoric) groups that can undergo hydrogen bonding, form complexes with metal ions, and interact with nanoparticles is scrutinized. Specific features of the structural organization of polymer mesophases are covered. The data on multifunctional comb-shaped LC polymers, LC ionomers, and LC dendrimers are examined, and the problems concerning the design of light-controllable LC copolymers and polymer photochromic composites and networks are reviewed. Some applied aspects of using LC polymers are considered: specifically, approaches to creation of lasers based on cholesterics and photo- and electroactive media in optics and photonics, systems for data recording and storage, holography, display technology, and other fields.