Photoactive Moieties Research Articles

Ligand-driven light-induced spin transition in spin crossover compounds

Spin crossover (SCO) coordination compounds that show bistability between low spin and high spin states are promising light-controllable molecular switches. Selective wavelength irradiation of the coordination centre at low temperatures is known as a light-induced excited spin state trapping (LIESST effect) and it leads to the modulation of physical properties of SCO materials on the macroscopic as well as on the molecular level. Another way to trigger the spin state conversion by light is based on the isomerization of photoactive ligand moieties. The ligand field strength is changed due to light-induced photoisomerization and, therefore, corresponding cis–trans or ring-closing/ring-opening isomeric couples might exhibit different spin states at isothermal conditions. Such an approach is called as ligand driven light-induced spin change (LD LISC effect). From the application point of view, it presents a promising alternative to the LIESST effect because it can operate at room temperature. This article is focused on the most interesting iron and cobalt SCO compounds with photoisomerizable ligands and provides the overview of achieving results based on the LD LISC effect.

Optical Control of Antimicrobial Activity in Quinolone Derivatives

A series of photoswitchable compounds based on the antibiotics nalidixic acid and ciprofloxacin has been designed and prepared. Different photoactive moieties have been used as templates in order to allow for the photocontrol of the antimicrobial properties while providing the adequate photophysical features and solubility required for practical applications. The designed compounds feature strong absorptions up to the visible region, are water‐soluble and photoisomerize with high quantum yield. In the best case, a clear difference in the antimicrobial activity expressed as the minimal inhibitory concentration between the initial and the irradiated species was found. The complementary computational study allowed for the rationalization of the results found.

Functionalization of MoS2 with 1,2-dithiolanes: toward donor-acceptor nanohybrids for energy conversion

The covalent functionalization of exfoliated semiconducting MoS2 by 1,2-dithiolanes bearing an ethylene glycol alkyl chain terminated to a butoxycarbonyl-protected amine and a photoactive pyrene moiety is accomplished. The MoS2-based nanohybrids were fully characterized by complementary spectroscopic, thermal, and microscopy techniques. Markedly, density functional theoretical studies combined with X-ray photoelectron spectroscopy analysis demonstrate preferential edge functionalization, primarily via sulfur addition along partially sulfur saturated zig-zag MoS2 molybdenum-edges, preserving intact the 2D basal structure of functionalized MoS2-based nanohybrids as confirmed by high-resolution transmission electron microscopy and electron energy loss spectroscopy. Furthermore, in the MoS2-pyrene hybrid, appreciable electronic interactions at the excited state between the photoactive pyrene and the semiconducting MoS2 were revealed as inferred by steady-state and time-resolved photoluminescence spectroscopy, implying its high potentiality to function in energy conversion schemes.

Photoactive Polymers with Benzocyclobutene/Silacyclobutane Dual Crosslinked Structure and Low Dielectric Constant

ABSTRACTLow dielectric photopatternable materials have aroused much interest owing to their potential application as alternatives of conventional photoresists. Although a number of photosensitive groups have been established to construct photopatternable materials for many years, it is still a challenge to introduce them into polymer chains via a facile and control polymerization technique, such as living free radical polymerization. In this work, on the basis of the photoactive silaycyclobutene moiety, a new monomer, 1‐methyl‐1‐(4‐vinylphenyl) silacyclobutane (1‐MVPSCB), was synthesized and demonstrated successful to conduct atom transfer radical polymerization (ATRP). Subsequently, the copolymerization of 1‐MVPSCB with 4‐vinylbenzocyclobutene (4‐VBCB) and styrene produced a kind of benzocyclobutene/silacyclobutane double‐crosslinked polymer (BS‐DCP) with controlled benzocyclobutene/silacyclobutane ratios and low polydispersity index. Owing to the UV/thermally dual crosslinked structure, BS‐DCP possesses photapatternability, high dimensional stability and low dielectric constant (2.37 at 10 MHz). These properties make BS‐DCP a potential photoresist that could be directly used as interconnected dielectrics. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1920–1928

Phototriggered release of tetrapeptide AAPV from coumarinyl and pyrenyl cages.

Ala-Ala-Pro-Val (AAPV) is a bioactive tetrapeptide that inhibits human neutrophil elastase, an enzyme involved in skin chronic inflammatory diseases like psoriasis. Caged derivatives of this peptide were prepared by proper N- and C-terminal derivatisation through a carbamate or ester linkage, respectively, with two photoactive moieties, namely 7-methoxycoumarin-2-ylmethyl and pyren-2-ylmethyl groups. These groups were chosen to assess the influence of the photosensitive group and the type of linkage in the controlled photo release of the active molecule. The caged peptides were irradiated at selected wavelengths of irradiation (254, 300, and 350nm), and the photolytic process was monitored by HPLC-UV. The results established the applicability of the tested photoactive groups for the release of AAPV, especially for the derivative bearing the carbamate-linked pyrenylmethyl group, which displayed the shortest irradiation times for the release at the various wavelengths of irradiation (ca. 4min at 254nm, 8min at 300nm and 46min at 350nm).

Multifunctional TiO2/FexOy/Ag based nanocrystalline heterostructures for photocatalytic degradation of a recalcitrant pollutant

The photocatalytic degradation of pollutants is a key technological application for nanomaterials. Our work aims at developing a multifunctional nanocrystalline heterostructure based on TiO2 nanorods, FexOy and Ag nanoparticles (NPs), TiO2NRs/FexOy/Ag, integrating in one nanostructure a visible light photoactive moiety (TiO2NRs/Ag) and a magnetic domain (FexOy), in order to address the photoactivity under visible light and the possibility of recovery and reuse the photocatalyst. The synthesis was carried by preparing first the TiO2NRs/FexOy based heterostructure and then growing Ag NPs with control on size. The resulting multidomain structures were characterized by FTIR and absorption spectroscopy, TEM and SEM microscopy, EDS and XRD analysis. The influence of the Ag NP domain and of its size on the photoactivity of the TiO2NRs/FexOy/Ag nanostructures under visible light were investigated in the photocatalytic degradation of the Nalidixic Acid, an antibiotic used as a model compound representative of recalcitrant pollutants. In the presence of the Ag domain a significant increase of the photoactivity with respect to TiO2NRs/FexOy heterostructures and to the commercially available TiO2 P25 was observed. Such an enhanced photocatalytic efficiency was found dependent on the size of the Ag domain and explained taking into account the plasmonic properties and the different possible photoactivation mechanisms.

Photoactive Metal-Organic Framework and Its Film for Light-Driven Hydrogen Production and Carbon Dioxide Reduction.

The design of a new photocatalytic system and integrating the essential components in a structurally controlled manner to create artificially photosynthetic systems is high desirable. By incorporating a photoactive triphenylamine moiety to assemble a Gd-based metal-organic framework as a heterogeneous photosensitizer, new artificial systems were constructed for the proton and carbon dioxide reduction under irradiation. The assembled MOFs exhibited a one-dimensional metal-oxygen pillar that was connected together by the depronated TCA(3-) ligands to form a three-dimensional noninterpenetrating porous framework. The combining of proton reduction and/or the carbon dioxide reduction catalysts, i.e., the Fe-Fe hydrogenase active site models and the Ni(Cyclam) complexes, initiated a photoinduced single electron transfer from its excited state to the substrate. The system exhibited an initial TOF of 320 h(-1) of hydrogen per catalyst and an overall quantum yield of about 0.21% and is able to reduce carbon dioxide under irradiation. The deposit of the photoactive Gd-TCA into the film of an α-Al2O3 plate provided a platform for the practical applications through prolonging the lifetime of the artifical system and allowed the easily operated devices being recyclable as a promising photocatalytic system.

Targeted photocytotoxicity by copper(II) complexes having vitamin B6 and photoactive acridine moieties

Copper(II) pyridoxal Schiff base complexes [Cu(L1/L2)(B)]ClO4 (1–4), where HL1 is 4-(((2-(1H-imidazol-4-yl)ethyl)imino)methyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol (in 1 and 2), HL2 is 2-(((2-(1H-imidazol-4-yl)ethyl)imino)methyl)phenol (in 3, 4), B is 11-(9-acridinyl)dipyrido[3,2-a:2′,3′-c]phenazine (acdppz in 1 and 3), dipyrido[3,2-a:2′,3′-c]phenazine (in 2) and 1,10-phenanthroline (in 4), were synthesized, characterized and their photocytotoxicity in visible light, intracellular localization, cellular uptake and DNA photocleavage activity were studied. Complex 4 was characterized by X-ray crystallography. Complexes 1 and 3 having acdppz as photosensitizer showed significant photocytotoxicity in visible light in HeLa and MCF7 cells giving IC50 value of <0.6 μM, while being relatively non-toxic in dark. The complexes were non-toxic to non-tumorigenic HPL1D cells both in light and dark conditions. Complex 1 showed significant localization in the cytoplasm of HeLa cells within 4 h of treatment, as evidenced from confocal microscopy. DCFDA assay on 1 suggested generation of intracellular reactive oxygen species in HeLa cells upon photo-exposure. Importantly, Annexin-V-FITC/PI assay indicated photo-induced apoptotic cell death.

Microcantilever arrays functionalised with spiropyran photoactive moieties as systems to measure photo-induced surface stress changes

Herein we investigate the feasibility of detecting photo-induced surface stress changes using the deflection response of cantilevers. For this purpose, silicon microcantilevers have been functionalised with spiropyran photochromic molecules, using both a monolayer and a polymeric brushes approach. Upon ultraviolet light irradiation, the spiropyran unit is converted to the merocyanine form due to the photo-induced cleavage of the Cspiro-O bond. The two forms of the molecule have dramatically different charge, polarity and molecular conformations. This makes spiropyrans an ideal system to study the correlation between photo-induced molecular changes and corresponding changes in surface stress. Our investigations include monitoring the changes in static cantilever deflection, and consequently, surface stress of the spiropyran functionalised cantilevers on exposure to ultraviolet light. Cantilever deflection data reveals that ultraviolet induced conformational changes in the spiropyran moiety cause a change in compressive surface stress and this varies with the type of functionalisation method implemented. The change in surface stress response from the spiropyran polymer brushes functionalised cantilevers gives an average surface stress change of 98 Nm−1 (n=24) while the spiropyran monolayer coated cantilevers have an average surface stress change of about 446 Nm−1 (n=8) upon irradiation with UV light.

Liquid crystalline dendrimers based on cinnamates and coumarins

ABSTRACTNew poly(propylene imine) (PPI) dendrimers modified at the periphery with mesomorphic 4-cyanobiphenyl units and cinnamate- or coumarin-based photoactive moieties were synthesised and structurally characterised. The photoactive moieties were structurally designed to be liquid crystalline compatible and to reduce the tendency towards crystallisation of the final material. Thermal and liquid crystal properties were studied by POM, DSC, TGA and XRD. The results show that all dendrimers displayed a smectic A mesophase. Dendrimers with high transparency in the visible region but with different absorption spectra were obtained, rendering materials that are easy to monitor in light-irradiation experiments.

Synthesis and application of photo-active carboxymethyl cellulose derivatives

In this work, the polysaccharide carboxymethyl cellulose (CMC) was first activated via periodate oxidation then modified by insertion of photo-active cinnamic acid hydrazide moieties to finally produce the photo-crosslinkable CMC-CM with various extents of functionalizations. The chemical structures of the manufactured polymeric materials were entirely investigated utilizing FTIR, 1H, 13C NMR, and UV–vis spectra. Upon irradiation in UV light, the progress and kinetics of the cross-linking were detected using UV–vis spectra. Moreover, the crystallinity changes before and after chemical modification and subsequent UV irradiation were examined by XRD spectra. Also, the obtained hydrogels with various cross-linking densities were freeze dried to visualize the morphological changes using SEM. In addition, the rheological experiments indicated the improvement of the hydrogel mechanical properties by increasing both UV irradiation time and degree of cinnamate functionalization. The obtained hydrogel exhibited good swelling, gelation and biodegradation properties, which indicate a promising potential in different biomedical applications.

Synthesis and characterization of photo-crosslinkable 4-styryl-pyridine modified alginate

In this article photo-crosslinkablestyryl-pyridine modified alginate (ASP-Alg) was prepared and entirely investigated utilizing different instrumental techniques such as Elemental analysis, Fourier transform infrared (FTIR),13C and 1H nuclear magnetic resonance (NMR), ultraviolet-visible light (UV-vis), X-ray diffraction (XRD) spectra and scanning electron microscope (SEM). Upon irradiation in the UV region, the casted ASP-Alg membranes were cross-linked through the [2π+2π] cycloaddition reaction of the inserted photo-active styryl pyridine moieties. Both cross-linking density and kinetics were monitored by examining the UV–vis light spectra of the irradiated membrane at predetermined time intervals and the obtained results were found to fit with the second order mathematical kinetic model, revealing the performance of the cross-linking via bimolecular [2π+2π] cycloaddition reaction. Also, the swelling behaviors along with biodegradability were also studied, and the results indicated the decrease of the swelling ratio and degradation rate by increasing the cross-linking density. Moreover, the mechanical properties were also examined under both wet and dry conditions.

Wavelength selective polymer network formation of end-functional star polymers.

A wavelength selective technique for light-induced network formation based on two photo-active moieties, namely ortho-methylbenzaldehyde and tetrazole is introduced. The network forming species are photo-reactive star polymers generated via reversible activation fragmentation chain transfer (RAFT) polymerization, allowing the network to be based on almost any vinylic monomer. Direct laser writing (DLW) allows to form any complex three-dimensional structure based on the photo-reactive star polymers.

Chromenes involving a two-photon absorbing moiety: photochromism via intramolecular resonance energy transfer

A general approach toward the synthesis of molecular dyads involving the photoactive moieties connected by a non-conjugative link is described.

Iron(III) salicylates of dipicolylamine bases showing photo-induced anticancer activity and cytosolic localization

An iron(III) salicylate having a dipicolylamine base (andpa) with a photoactive anthracenyl moiety is prepared, characterized, and studied for its photo-induced anticancer activity and cellular localization in HeLa and MCF-7 cells. Its phenyl analogue is structurally characterized by X-ray crystallography. The complex has a ternary structure in which the dipicolylamine ligand and salicylic acid in dianionic form (sal) display respective tridentate and bidentate mode of coordination in [Fe(sal)(phdpa)Cl] (1). Complex [Fe(sal)(andpa)Cl] (2) having a pendant anthracenyl moiety shows significant photocytotoxicity in visible light (400–700nm) giving IC50 values of 8.6±0.7 and 3.4±0.9μM in HeLa and MCF-7 cells, while being essentially nontoxic in the dark (IC50>100μM). The complex shows cytosolic localization in the cancer cells. Formation of hydroxyl radicals (OH) as the reactive oxygen species is evidenced from the pUC19 DNA photocleavage studies.

Controlled Formation of Star Polymer Nanoparticles via Visible Light Photopolymerization.

A recently developed visible light mediated photocontrolled radical polymerization technique using trithiocarbonates (i.e., conventional RAFT agents) as the sole control agent in the absence of additional photoinitiators or catalysts is utilized for the synthesis of core cross-linked star (CCS) polymer nanoparticles. The attractive features of this photopolymerization system, including high end-group fidelity at (near) complete monomer conversion, are exploited to facilitate a high-yielding, one-pot pathway toward well-defined star polymer products. Moreover, reinitiation of the photoactive trithiocarbonate moieties from within the star core is demonstrated to form (pseudo)miktoarm stars via an "in-out" approach, showing extremely high initiation efficiency (95%).

Phototriggered functionalization of hierarchically structured polymer brushes.

The precise design of bioactive surfaces, essential for the advancement of many biomedical applications, depends on achieving control of the surface architecture as well as on the ability to attach bioreceptors to antifouling surfaces. Herein, we report a facile avenue toward hierarchically structured antifouling polymer brushes of oligo(ethylene glycol) methacrylates via surface-initiated atom transfer radical polymerization (SI-ATRP) presenting photoactive tetrazole moieties, which permitted their functionalization via nitrile imine-mediated tetrazole-ene cyclocloaddition (NITEC). A maleimide-functional ATRP initiator was photoclicked to the side chains of a brush enabling a subsequent polymerization of carboxybetaine acrylamide to generate a micropatterned graft-on-graft polymer architecture as evidenced by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Furthermore, the spatially resolved biofunctionalization of the tetrazole-presenting brushes was accessed by the photoligation of biotin-maleimide and subsequent binding of streptavidin. The functionalized brushes bearing streptavidin were able to resist the fouling from blood plasma (90% reduction with respect to bare gold). Moreover, they were employed to demonstrate a model biosensor by immobilization of a biotinylated antibody and subsequent capture of an antigen as monitored in real time by surface plasmon resonance.

Photosensitization by imatinib. A photochemical and photobiological study of the drug and its substructures.

Imatinib (IMT) is a promising tyrosine kinase inhibitor used in the treatment of some types of human cancer. It constitutes a successful example of rational drug design based on the optimization of the chemical structure to reach an improved pharmacological activity. Cutaneous reactions, such as increased photosensitivity or pseudoporphyria, are among the most common nonhematological IMT side effects; however, the molecular bases of these clinical observations have not been determined. Thus, to gain insight into the IMT photosensitizing properties, we addressed its photobehavior together with that of its potentially photoactive anilino-pyrimidine and pyridyl-pyrimidine fragments. In this context, steady-state and time-resolved fluorescence as well as laser flash photolysis experiments have been conducted, and the DNA photosensitization potential has been investigated by means of single-strand break detection using agarose gel electrophoresis. The obtained results reveal that the drug itself and its anilino-pyrimidine fragment are not DNA photosensitizers. By contrast, the pyridyl-pyrimidine substructure displays a marked phototoxic potential, which has been associated with the generation of a long-lived triplet excited state. Interestingly, this reactive species is efficiently quenched by benzanilide, another molecular fragment of IMT. Clearly, integration of the photoactive pyridyl-pyrimidine moiety in a more complex structure strongly modifies its photobehavior, which in this case is fortunate as it leads to an improved toxicological profile. Thus, on the bases of the experimental results, direct in vivo photosensitization by IMT seems unlikely. Instead, the reported photosensitivity disorders could be related to indirect processes, such as the previously suggested impairment of melanogenesis or the accumulation of endogenous porphyrins.

Encapsulation of phthalocyanine-C$_{60}$ fullerene conjugates into metallosupramolecular subphthalocyanine capsules: a turn of the screw

In this communication, encapsulation studies between metallosupramolecular capsule 1, formed by 2 subphthalocyanines (SubPcs) coordinated to 3 metallic centers, and phthalocyanine (Pc)-C_{60} fullerene conjugates 2--5 have been carried out. It was shown that the encapsulation of the C_{60} moiety by the SubPc cage occurred exclusively for dyads 2--4, whereas it was not observed in the case of triad 5. The rigidity of the linker between the Pc and the fullerene unit proved to have an important impact in the complex formation. Complex formation was tested in 2 different solvents, where the importance of solvophobic effects was highlighted. The resulting multicomponent supramolecular systems represent a unique combination of photoactive moieties where covalent and supramolecular chemistry coexist.

Azobenzene moiety variation directing self-assembly and photoresponsive behavior of azo-surfactants

We report two photoresponsive amphiphiles with comparable structures consisting of hydrophilic oligooxyethylene units, a hydrophobic alkyl chain and a light-sensitive azobenzene moiety, demonstrating that self-assembly and photoresponsive behaviour is extremely sensitive to the position of the photoactive moiety within the surfactant molecular architecture.