Photoactive Moieties Research Articles

Synthesis of orthogonally addressable block copolymers via reversible addition fragmentation chain transfer polymerization and subsequent chemoselective postmodification

ABSTRACTThis article describes the synthesis of bifunctional block copolymers (BCPs) of type 4 bearing orthogonally reactive backbone substituents such as 1,1,1,3,3,3‐hexafluoroisopropoxycarbonyl groups as active esters and α‐hydroxyalkylphenylketones (2‐hydroxy‐2‐methyl‐1‐phenylpropan‐1‐one) as additional photoactive moieties via reversible addition fragmentation chain transfer (RAFT) polymerization. As monomers 1,1,1,3,3,3‐hexafluoroisopropyl acrylate (HFIPA) and 2‐hydroxy‐2‐methyl‐1‐(4‐vinyl)phenylpropan‐1‐one (HAK) are used. Controlled radical polymerization provides BCPs p(HFIPA)‐b‐p(HAK) with molecular weights (Mn) ranging from 15,000 to 37,000 g mol−1 and low molecular weight distributions (PDI = 1.2–1.4). The incorporated HFIPA and HAK moieties are used for sequential chemoselective postmodification of 4. The photoactive block of 4 can be functionalized through a nitroxide photoclick trapping reaction in the presence of functionalized nitroxides and the active ester moieties of the p(HFIPA)‐block are readily thermally amidated using various amines. Chemically modified polymers are characterized by NMR, FTIR, and GPC methods which reveal a high degree of postfunctionalization, typically >95% for both orthogonal processes. The chemically modified polymers feature a narrow molecular weight distribution. The process is successfully applied to the synthesis of a small polymer library and also to the preparation of homo and block polynitroxides using 4‐amino‐TEMPO as amine component in the transamidation reaction. The polynitroxides obtained are characterized by cyclic voltammetry, FTIR, and UV–vis spectroscopy. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 52, 258–266

ON-OFF Luminescence Signaling of Hybrid Organic–Inorganic Switches

The dyads 1OFF and 2OFF were prepared by combining the inorganic luminophores [Ru(phen)2(2-[imidazol-2-yl]pyridine)](2+) and [Re(CO)3Cl(2-[imidazol-2-yl]pyridine)] with 2-(anthracen-9-yl)-4-methylphenol as a second photoactive moiety. In both cases, the inorganic unit operates as the emitter, whereas the organic part acts as a controller. Emission of the inorganic luminophore can be reversibly switched ON and OFF by adjusting the energetic level of the (3)π-π* state of the appended anthracene unit through either dearomatization using a photohydration or aromatization applying a thermal dehydration. Emission of both switches is reversibly recorded and erased multiple times without significant degradation.

Photocatalytic Conversion of CO2 to CO using Rhenium Bipyridine Platforms Containing Ancillary Phenyl or BODIPY Moieties.

Harnessing of solar energy to drive the reduction of carbon dioxide to fuels requires the development of efficient catalysts that absorb sunlight. In this work, we detail the synthesis, electrochemistry and photophysical properties of a set of homologous fac-ReI(CO)3 complexes containing either an ancillary phenyl (8) or BODIPY (12) substituent. These studies demonstrate that both the electronic properties of the rhenium center and BODIPY chromophore are maintained for these complexes. Photolysis studies demonstrate that both assemblies 8 and 12 are competent catalysts for the photochemical reduction of CO2 to CO in DMF using triethanolamine (TEOA) as a sacrificial reductant. Both compounds 8 and 12 display TOFs for photocatalytic CO production upon irradiation with light (λex ≥ 400 nm) of ~5 hr-1 with TON values of approximately 20. Although structural and photophysical measurements demonstrate that electronic coupling between the BODIPY and fac-ReI(CO)3 units is limited for complex 12, this work clearly shows that the photoactive BODIPY moiety is tolerated during catalysis and does not interfere with the observed photochemistry. When taken together, these results provide a clear roadmap for the development of advanced rhenium bipyridine complexes bearing ancillary BODIPY groups for the efficient photocatalytic reduction of CO2 using visible light.

A new approach to light-gated Pt catalysts for the hydrosilylation

A new concept for a light-gated transition metal catalyst is presented based on a photo-active moiety in the outer ligand sphere of the complex which on irradiation reacts irreversibly with some part of the inner ligand sphere releasing a free coordination site. The principle is exemplified on a platinum complex for the hydrosilylation. It is proven that the catalytic properties of the complex and the properties of the photo-gate can be fine-tuned on the chemical problem independently of each other.

Chemical Modification of Polymer Brushes via Nitroxide Photoclick Trapping

The preparation of polymer brushes (PBs) bearing α-hydroxyalkylphenylketone (2-hydroxy-2-methyl-1-phenylpropan-1-one) moieties as photoreactive polymer backbone substituents is presented. Photoreactive polymer brushes with defined thicknesses (up to 60 nm) and high grafting densities are readily prepared by surface initiated nitroxide mediated radical polymerization (SINMP). The photoactive moieties can be transformed via Norrish-type I photoreaction to surface-bound acyl radicals. Photolysis in the presence of a persistent nitroxide leads to chemically modified PBs bearing acylalkoxyamine moieties as side chains resulting from trapping of the photogenerated acyl radicals with nitroxides. Application of functionalized nitroxides to the photochemical PB postmodification provides functionalized PBs bearing cyano, polyethylene glycol (PEG), perfluoroalkyl, and biotin moieties. As shown for one case, photochemical postfunctionalization of the PB through a mask using a biotin-conjugated nitroxide as the trapping reagent leads to the corresponding site-selective chemically modified PB, which is successfully used for site-specific streptavidin immobilization. Surface analysis of PBs was performed by contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), attenuated total reflection (ATR), fourier transform infrared (FTIR) spectroscopy, and fluorescence microscopy.

Tandem Synthesis of Photoactive Benzodifuran Moieties in the Formation of Microporous Organic Networks

Tandem Synthesis of Photoactive Benzodifuran Moieties in the Formation of Microporous Organic Networks

Tandem Synthesis of Photoactive Benzodifuran Moieties in the Formation of Microporous Organic Networks

Tandem Synthesis of Photoactive Benzodifuran Moieties in the Formation of Microporous Organic Networks

Photografting as a versatile, localizable, and single‐step surface functionalization of silica‐based monoliths dedicated to microscale separation techniques

In this work, we developed a surface functionalization way of silica monoliths with a rapid, simple, versatile, and localizable photografting step. The elaboration of a photoreactive layer at the surface of monoliths was first optimized. The functionalization with [γ-(methacryloyloxy)propyl]trimethoxysilane at 80°C in a hydro-organic solution containing triethylamine as catalyst allows reachng the highest density of methacrylate photoactive moieties on silica surfaces. These methacrylate reactive surfaces were subsequently photografted within few minutes with acrylate monomers bearing alkyl chains (C12 and C18). The photografting efficiency was determined by monitoring the retentive properties of monoliths in the RP mode. The retention factors are of the same order of magnitude as highly retentive columns obtained by modification of silica surface with long-alkyl chain silanes or by thermal polymerization of long-alkyl chain monomers. It was also verified that such grafting neither impaired the efficiency of the monolithic stationary phase (Hmin = 6-8 μm in nano-LC) nor its permeability (about 6 × 10(-14) m(2)). Further, it was also demonstrated that photografting is localizable in nonmasked defined areas. Results obtained in anion-exchange chromatography after photopolymerization of [2-(methacryloyloxy)ethyl]trimethylammonium chloride are presented as well to demonstrate the versatility of the developed approach.

Förster resonance energy transfer and carbon dots enhance light harvesting in a solid-state quantum dot solar cell

A novel yet inexpensive quantum dot solar cell (QDSC) configuration relying on Forster resonance energy transfer (FRET) from electrode bound excited cadmium sulfide (CdS) quantum dots ensconced in zinc sulfide (ZnS) monolayers to unattached copper phthalocyanine (CuPc) molecules, dissolved in a free standing sulfide ion based gel polymeric electrolyte, is presented. Luminescent and conducting carbon dots (C-dots) are incorporated in the anode to improve the electron transfer and transport characteristics of the photoactive assembly. Fluorescence quenching and lifetime measurements provide unambiguous proof of dominant energy and not electron transfer from the blue/green absorbing ZnS/CdS/ZnS donor QDs to the red absorbing CuPc acceptor molecules. The subsequent charge transfer rate from CuPc to the current collector via C-dots in the ZnS/CdS/ZnS/C-dot/CuPc assembly is faster and the electron recombination lifetime (with the oxidized species in the electrolyte, τ) is longer, in contrast with the slower rate and shorter τ in the assembly devoid of C-dots, thus confirming the role of C-dots in facilitating charge propagation. The Forster radius calculated from the overlap integral and the actual separation estimated from high resolution transmission electron microscopy between the CdS and CuPc are close, and the energy transfer efficiency is deduced to be 40%. Incident photon to current conversion efficiency (IPCE) measurements revealed an optimal coverage of the visible spectrum for the cells with both donors and acceptors: the ZnS/CdS/ZnS/C-dot/CuPc assembly shows a 5.76 times increment of photocurrent in the blue/green region in comparison with cells with only donor (ZnS/CdS/ZnS). The demonstration of a quasi solid-state FRET enabled cell not only opens up avenues to use photoactive moieties that do not undergo charge transfer as dictated by conventional energy level offsets, but also shows the viability of producing laminated, cheap QDSCs capable of harvesting broader regions of the visible spectrum.

Sol–gel conversion based on photoswitching between noncovalently and covalently linked netlike supramolecular polymers

Photo-control over supramolecular sol-gel conversion is achieved by incorporating photoactive coumarin moieties into a tribranched monomer and the self-assembly with γ-CD followed by noncovalent-covalent switchover.

Photo-induced anticancer activity of polypyridyl platinum(II) complexes

Polypyridyl platinum(II) complexes (1–5), viz., [Pt(pyphen)Cl]Cl (1), [Pt(pyphen)(C≡CFc)]Cl (2), [Pt(pydppz)Cl]Cl (3), [Pt(pydppz)(C≡CPh)]Cl (4) and [Pt(pydppz)(C≡CFc)]Cl (5), where pyphen is 6-(2-pyridyl)-1,10-phenanthroline, pydppz is 6-(2-pyridyl)-dipyrido-[3,2-a:2′,3′-c]-phenazine, FcC≡CH is ferrocenyl acetylene and PhC≡CH is phenyl acetylene, were synthesized, characterized and their DNA binding and photocytotoxic properties studied. The complexes showed strong binding affinity to calf-thymus DNA giving Kapp of ∼106–107 M−1. Complexes 4 and 5 showed dual mode of binding to ct-DNA. The pydppz complexes 3–5 having a photoactive phenazine moiety showed photocytotoxicity in HeLa and MCF-7 cells in UV-A light of 365 nm with apoptotic cell death as evidenced from the acridine orange/ethidium bromide dual staining and the FACS data.

Photoinduced Polymer Chain Scission of Alkoxyphenacyl Based Polycarbonates.

We report the design and development of a new class of alkoxyphenacyl based photodegradable polycarbonates. These polymers incorporate the photoactive moiety in the backbone and, when irradiated at 300 nm, undergo controlled chain scission. Micropatterned thin films of these polymers were fabricated by photolithographic techniques. The use of these photodegradable polymers for controlled release applications was demonstrated by the release of Nile Red from polymeric nanoparticles. In addition, these polymers are mechanically robust, thermally stable, and hydrolytically degradable.

酞菁-富勒烯给受体体系研究进展

Phthalocyanine possesses strong electron-donating ability and visible light absorbing property due to the large p conjugated system, which makes it a good light-harvesting antenna for artificial photosynthetic systems. Meanwhile, the excellent electron-accepting property of fullerene C 60 , together with its lower organization energy, renders this spherical carbon cage a perfect acceptor for photo- and electroactive molecular systems. The combination of phthalocyanine and fullerene in one compound provides the system with new properties due to the interaction between the two photoactive moieties. As such, these systems display good application prospect and are hot topics in related research fields. In this review, the structures and properties of covalent and supramolecular noncovalent phthalocyanine-fullerene systems and their relationship are introduced. Moreover, the recent application progress of these systems in the fields of organic solar cell, nonlinear optics and liquid crystal property is summarized, and their future development trend is prospected.

Evaluation of substrate and inhibitor binding to yeast and human isoprenylcysteine carboxyl methyltransferases (Icmts) using biotinylated benzophenone-containing photoaffinity probes

Isoprenylcysteine carboxyl methyltransferases (Icmts) are a class of integral membrane protein methyltransferases localized to the endoplasmic reticulum (ER) membrane in eukaryotes. The Icmts from human (hIcmt) and Saccharomyces cerevisiae (Ste14p) catalyze the α-carboxyl methyl esterification step in the post-translational processing of CaaX proteins, including the yeast a-factor mating pheromones and both human and yeast Ras proteins. Herein, we evaluated synthetic analogs of two well-characterized Icmt substrates, N-acetyl-S-farnesyl-l-cysteine (AFC) and the yeast a-factor peptide mating pheromone, that contain photoactive benzophenone moieties in either the lipid or peptide portion of the molecule. The AFC based-compounds were substrates for both hIcmt and Ste14p, whereas the a-factor analogs were only substrates for Ste14p. However, the a-factor analogs were found to be micromolar inhibitors of hIcmt. Together, these data suggest that the Icmt substrate binding site is dependent upon features in both the isoprenyl moiety and upstream amino acid composition. Furthermore, these data suggest that hIcmt and Ste14p have overlapping, yet distinct, substrate specificities. Photocrosslinking and neutravidin–agarose capture experiments with these analogs revealed that both hIcmt and Ste14p were specifically photolabeled to varying degrees with all of the compounds tested. Our data suggest that these analogs will be useful for the future identification of the Icmt substrate binding sites.

Synthesis, Structural Characterization, and Sensing Properties of Clickable Unsymmetrical 1,1′-Disubstituted Ferrocene–Triazole Derivatives

A variety of unsymmetrically 1,1′-disubstituted ferrocenes 3–5 have been prepared by using the tandem click reaction/Staudinger-azaWittig process and their cation complexation properties studied using electrochemical and spectroscopic techniques. The common structural features present in these ligands are the presence of another redox unit, connected to the 1-position of the central ferrocene core through a triazole ring, and a photoactive moiety linked to the 1′ -position of such core through an imine group. Receptors 3 and 5 undergo perturbation of the CV in the presence of Pb2+ and Zn2+ cations, whereas receptor 4 undergoes a different type of perturbation in the presence of Ni2+, Cd2+, Zn2+, and Pb2+ cations. The low-energy band of the absorption spectra of receptor 3 is blue-shifted, upon addition of Zn2+, and Pb2+ cations, whereas receptor 4 in the presence of Ni2+ and Cd2+ undergoes a remarkable red shift (Δλ = 110 nm) of the LE band which is responsible for the change of color from red to blue. Moreover, receptor 3 underwent a significant increase in its emission band in the presence of Pb2+, whereas in receptor 5, such an increase is notably lower. In conclusion, receptor 4 behaves as a colorimetric receptor for Ni2+and Cd2+ and 5 acts as a selective fluorescent receptor for the Pb2+ cation. On the basis of the 1H NMR titration data and from the DFT theoretical calculations, tentative binding modes have been proposed for the metal complexes formed.

Synthesis and Photophysical Properties of Fullerene–Phthalocyanine–Porphyrin Triads and Pentads

The synthesis and photophysical properties of several fullerene-phthalocyanine-porphyrin triads (1-3) and pentads (4-6) are described. The three photoactive moieties were covalently connected in an one-step synthesis through 1,3-dipolar cycloaddition to C(60) of the corresponding azomethine ylides generated in situ by condensation reaction of a substituted N-porphyrinylmethylglycine derivative and an appropriated formyl phthalocyanine or a diformyl phthalocyanine derivative, respectively. ZnP-C(60)-ZnPc (3), (ZnP)(2)-ZnPc-(C(60))(2) (6), and (H(2)P)(2)-ZnPc-(C(60))(2) (5) give rise upon excitation of their ZnP or H(2)P components to a sequence of energy and charge-transfer reactions with, however, fundamentally different outcomes. With (ZnP)(2)-ZnPc-(C(60))(2) (6) the major pathway is an highly exothermic charge transfer to afford (ZnP)(ZnP(.+))-ZnPc-(C(60)(.-))(C(60)). The lower singlet excited state energy of H(2)P (i.e., ca. 0.2 eV) and likewise its more anodic oxidation (i.e., ca. 0.2 V) renders the direct charge transfer in (H(2)P)(2)-ZnPc-(C(60))(2) (5) not competitive. Instead, a transduction of singlet excited state energy prevails to form the ZnPc singlet excited state. This triggers then an intramolecular charge transfer reaction to form exclusively (H(2)P)(2)-ZnPc(.+)-(C(60)(.-))(C(60)). A similar sequence is found for ZnP-C(60)-ZnPc (3).

Location of the Azobenzene Moieties within the Cross-Linked Liquid-Crystalline Polymers Can Dictate the Direction of Photoinduced Bending.

We present a simple way to control the photoinduced bending direction of azobenzene-containing cross-linked liquid-crystalline polymers. By changing the location of the photoactive azobenzene moieties from cross-links to side-chains, the bending direction of the sample is reversed under identical irradiation conditions. In addition to providing a versatile route toward directionality control of the photoinduced macroscopic motions, this observation highlights the complicated nature of the photomechanical response of azobenzene-containing cross-linked liquid-crystalline polymers, showing that the photomobile behavior can be determined by seemingly small details on the materials design.

Identification of the PGRMC1 protein complex as the putative sigma-2 receptor binding site

The sigma-2 receptor, whose gene remains to be cloned, has been validated as a biomarker for tumor cell proliferation. Here we report the use of a novel photoaffinity probe, WC-21, to identify the sigma-2 receptor binding site. WC-21, a sigma-2 ligand containing both a photoactive moiety azide and a fluorescein isothiocyanate group, irreversibly labels sigma-2 receptors in rat liver; the membrane-bound protein was then identified as PGRMC1 (progesterone receptor membrane component-1). Immunocytochemistry reveals that both PGRMC1 and SW120, a fluorescent sigma-2 receptor ligand, colocalizes with molecular markers of the endoplasmic reticulum and mitochondria in HeLa cells. Overexpression and knockdown of the PGRMC1 protein results in an increase and a decrease in binding of a sigma-2 selective radioligand, respectively. The identification of the putative sigma-2 receptor binding site as PGRMC1 should stimulate the development of unique imaging agents and cancer therapeutics that target the sigma-2 receptor/PGRMC1 complex.

Polymer-Based Photocoupling Agent for the Efficient Immobilization of Nanomaterials and Small Molecules

A highly efficient photocoupling agent, based on perfluorophenylazide (PFPA)-conjugated polyallylamine (PAAm), was developed for the efficient immobilization of polymers, nanoparticles, graphene, and small molecules. The conjugate, PAAm-PFPA, was synthesized, and the percentage of the photoactive moiety, PFPA, can be controlled by the ratio of the two components in the synthesis. By treating epoxy-functionalized wafers with PAAm-PFPA, photoactive surfaces were generated. Compared with the PFPA surface, these polymer-based photocoupling matrix resulted in significantly enhanced immobilization efficiencies, especially for nanomaterials and small molecules. Thus, polystyrene nanoparticles (PS NPs) and alkyl-functionalized silica nanoparticles (SNPs) were successfully immobilized on the PAAm-PFPA surface, resulting in a high material density. Graphene flakes patterned on the PAAm-PFPA surface showed improved feature resolution in addition to a higher material density compared to that of flakes immobilized on the PFPA surface. Furthermore, 2-O-α-D-mannopyranosyl-D-mannopyranose (Man2) immobilized on the PAAm-PFPA surface exhibited significantly enhanced signals when treated with lectin concanavalin A (Con A).

Photo-activated cytotoxicity of a pyrenyl-terpyridine copper(II) complex in HeLa cells

Terpyridine copper(II) complexes [Cu(L) 2](NO 3) 2, where L is (4′-phenyl)-2,2′:6′,2′′-terpyridine (ph-tpy in 1) and [4′-(1-pyrenyl)]-2,2′:6′,2′′-terpyridine (py-tpy in 2), are prepared, characterized and their photocytotoxic activity studied. The crystal structure of complex 1 shows distorted octahedral CuN 6 coordination geometry. The 1:2 electrolytic and one-electron paramagnetic complexes show a visible band near 650 nm in DMF–H 2O. The complexes show emission band at 352 nm for 1 and 425 nm for 2 when excited at 283 and 346 nm, respectively. The Cu(II)–Cu(I) redox couple is observed near −0.2 V versus SCE in DMF–0.1 M TBAP. The complexes are avid partial-intercalative binders to calf thymus DNA giving binding constant ( K b) values of ∼10 6 M −1. Complex 2 with its photoactive pyrenyl moiety exhibits significant photocleavage of pUC19 DNA in red light via singlet oxygen pathway. Complex 2 also exhibits significant photo-activated cytotoxicity in HeLa cancer cells in visible light giving IC 50 value of 11.9 μM, while being non-toxic in dark with an IC 50 value of 130.5 μM.