Photoinitiated Reaction Research Articles

Influence of the structure of nanoscopic building blocks on the assembly of micropatterned surfaces

AbstractThe effect of solution‐state nanoscale structures on the assembly of micropatterns by solvent evaporation was explored with a novel amphiphilic diblock copolymer synthesized by reversible addition–fragmentation chain transfer polymerization. A copolymer of the structure poly(styrene‐alt‐maleic anhydride)75‐b‐isoprene84 was assembled into inverse micelles in toluene, and covalently stabilized in the core by reactive amidation of maleic anhydride residues with 2,2′‐(ethylenedioxy)bis(ethylamine) to create core‐crosslinked nanoparticles (CCNPs) or in the shell by the photoinitiated radical crosslinking reactions of isoprene units to create large crosslinked aggregates (LCAs) of heterogeneous sizes and shapes. Micropatterned films were prepared by the deposition of the diblock copolymer as a solution in acetone and the nanoscale structures (inverse micelle, crosslinked aggregate, and CCNP) as solutions in toluene onto trimethylysilyl chloride treated glass microscope slides under ambient conditions. An analysis by optical microscopy and tapping‐mode atomic force microscopy (AFM) indicated that the nanoscale surface topology could be controlled by the pre‐establishment of the block copolymer phase segregation into well‐defined core–shell nanoassemblies in solution. The most interesting films resulted from the evaporative deposition of inverse micelle and CCNP solutions, which afforded uniform, straplike micropatterns of similar dimensions on the microscale and low surface roughness on the nanoscale (roughness = 4 ± 1 and 6± 1 nm by AFM). © 2006 Wiley Periodicals, Inc. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5218–5228, 2006

Antibody-modified microwell arrays and photobiotin patterning on hydrocarbon-free glass

Antibody-modified microwell arrays were fabricated using site-selective photobiotin chemistry and the biotin–avidin interaction. In one scheme, an aminopropyl-functionalized glass surface was the starting substrate and in the other an acid-treated glass surface was employed. In both schemes, the substrates were coated with the aryl azide photobiotin, and photoactivated with ultraviolet radiation to afford biotin-modified arrays before sequential reactions with ExtrAvidin, biotinylated-IgG, and dye-labeled anti-IgG. Antibody-modified microwell arrays were characterized using fluorescence microscopy. In both schemes, the biotin–avidin–biotin linkage was stable, and there was negligible non-specific binding (NSB) of photobiotin, ExtrAvidin, and dye-labeled anti-IgG to the modified substrates. However, negligible NSB of biotinylated-IgG was observed only with the acid-treated glass surface. To further characterize the nitrene reactions on these hydrocarbon-free glass surfaces, we developed a new protocol using a fluorescent-labeled aryl azide in place of photobiotin. Fluorescence microscopy characterizations of these modified surfaces revealed that detectable fluorescence was observed only from silanol-rich, acid-treated glasses. It is believed this work represents the first demonstration of photo-initiated reactions of photobiotin with reactive silanols on acid-treated glass surfaces.

Photo-curing modelling: direct irradiation

Thermosetting resins are converted into three-dimensional networks via a polymerisation reaction known as cure. This reaction determines the resin morphology that, in turn, will determine the physical, electrical, and mechanical properties of the cured material. Moreover, the cure reaction of thermosets is exothermic and polymers exhibit low thermal conductivity so the temperature and rate of reaction can vary considerably within the curing mass. Simulations of the behaviour of these materials require analytical models accurately describing its cure kinetics. An integrated thermal-kinetic model is presented to study photo-initiated curing reactions and determine different aspects associated with these reactions, describing both the heat transfer phenomenon all along the reaction and the cure kinetics. This model is sensitive to the resin composition, temperature and light intensity, apart from describing the main events occurring during cure reactions. The kinetic model and the law of the conservation of energy are coupled, while the integrated model is numerically solved.

Different mechanisms both lead to the production of the naphthalene–OH adduct in the 355 nm and 266 nm laser flash photolysis of the mixed aqueous solution of naphthalene and nitrous acid

The 355 nm and 266 nm nanosecond laser flash photolysis of the mixed aqueous solution of naphthalene (Np) and nitrous acid (HNO 2) were performed to investigate the photo-initiated microscopic reactions in this binary component system. Following the 355 nm laser flash, HNO 2 was readily photolyzed to NO and OH, and the latter fragment added to the Np ring to form the Np–OH adduct at the rate constant of (1.1 ± 0.1) × 10 10 M −1 s −1. Following the 266 nm laser flash, Np was populated first to its lowest excited singlet state (S 1) and then to its lowest excited triplet state (T 1) via intersystem crossing. Np(S 1) and Np(T 1) both formed the [Np···HNO 2] * exciplex with HNO 2, and the fast dissociation of this exciplex again produced the Np–OH adduct. The second-order quenching rate constants of Np(S 1) and Np(T 1) by HNO 2 were measured to be (6.0 ± 0.2) × 10 9 M −1 s −1 and (4.8 ± 0.2) × 10 9 M −1 s −1, respectively. It was very interesting to conclude that although both the 355 nm and the 266 nm irradiation of the mixed aqueous solution of Np and HNO 2 produced the Np–OH adduct, the mechanisms leading to this species varied essentially for the two cases. This work suggested an unexpected way of releasing OH by HNO 2 other than its direct photolysis, namely via forming exciplex with the excited Np (and possibly other polycyclic aromatic hydrocarbons, PAHs) in the environment.

The participation of the anion and alkyl substituent of diaryliodonium salts in photo-initiated cationic polymerization reactions

The photo-initiated cationic polymerization (PCP) of epoxides using diaryliodonium salt photoacid generators (PAGs) bearing alkyl groups and anions was investigated. The properties and reactivities of a series of iodonium salts containing various cations and anions were compared in the context of a PCP reaction. The products from the decomposition of the cations of these salts were analyzed using gas chromatography-mass spectrometry (GC-MS) spectra. The relationship between the molecular structure of the salts and their reaction mechanism in the PCP reaction was investigated. Based on the results of the investigation, it was concluded that the structures of the cations and anions of theiodonium salts affect the PCP reaction rate, which was controlled by the products from the diaryliodonium salts. As part of an additional investigation, the diaryliodonium salts-epoxide materials were applied to 254 nm-photo-patterning. Copyright © 2006 John Wiley & Sons, Ltd.

Fluorescence monitoring of photoinitiated polymerization reactions: Synthesis, photochemical study and behaviour as fluorescent probes of new derivatives of 4′-dimethylaminostyryldiazines

The fluorescence emission of three new fluorescent probes has been studied in environments of different polarity and viscosity. The diazine moieties behave as electron acceptor and a good correlation has been found between their reduction potentials and the dipole moments in the excited state (estimated from solvatochromic plots using Lippert equations). The probes have shown to be sensitive to changes in both microviscosity and micropolarity of the surroundings. They have been used as fluorescent sensors to monitor the photopolymerization reactions of some mono- and difunctional methacrylate monomers in bulk. The fluorescence emission band of the probes showed an increase in intensity, as well as an hypsochromic shift, as the degree of conversion increases, throughout the entire polymerization range in the different systems checked.

Spectroscopic and Theoretical Evidence for the Elusive Intermediate of the Photoinitiated and Thermal Rearrangements of Photochromic Spiropyrans

Spectral properties and photochromic behavior of a series of novel 1',3',3'-trimethyl-1,2-tetramethylenespiro[7H-furo(3,2-f)-(2H-1)-benzopyran-7,2'-indolines] 1-4 have been studied. The mechanism of the photoinitiated ring-opening reaction involves the formation of an acoplanar cis-cisoid intermediate, the lifetime of which in the case of 6-(tert-butyl) derivative 4 is long enough to observe its absorption and fluorescence spectra under conditions of continuous irradiation. The occurrence of the intermediate on the reaction paths of the thermal and photochemical ring-opening processes has been also shown by the DFT and CIS calculations. The TD-B3LYP/6-31G//HF/6-31G calculated spectrum of the intermediate well matches that observed experimentally. For spiropyran 3 with a 6-NO(2) group, kinetic and activation parameters of the photoinitiated coloration and dark bleaching reactions have been determined.

Monolayer-Protected Gold Nanoparticle Coalescence Induced by Photogenerated Radicals

Acyl and alkyl radicals generated photochemically in a solution containing monolayer-protected gold nanoparticles are shown to efficiently liberate the alkylthiolate ligands into the solution as the thioacetyl or alkyl sulfide, respectively. This radical-induced reaction initiates a coalescence of the gold cores to facilitate an increase in core size. The photoinitiated radical reaction also liberates monolayers from two-dimensional gold surfaces.

Collisional and photoinitiated reaction dynamics in the ground electronic state of Ca–HCl

Ca+HCl(upsilon,j) reactive collisions were studied for different rovibrational states of the HCl reactant using wave-packet calculations in reactant Jacobi coordinates. A recently proposed potential-energy surface was used with a barrier of approximately 0.4 eV followed by a deep well. The possibility of an insertion mechanism due to this last well has been analyzed and it was found that once the wave packet passes over the barrier most of it goes directly to CaCl+H products, which shows that the reaction dynamics is essentially direct. It was also found that there is no significant change in the reaction efficiency as a function of the initial HCl rovibrational state, because CaHCl at the barrier has an only little elongated HCl bond. Near the threshold for reaction with HCl(upsilon=0), however, the reaction shows significant steric effects for j > 0. In a complementary study, the infrared excitation from the Ca-HCl van der Waals well was simulated. The spectrum thus obtained shows several series of resonances which correspond to quasibound states correlating to excited HCl(upsilon) vibrations. The Ca-HCl binding energies of these quasibound states increase dramatically with upsilon, from 75 to 650 cm(-1), because the wave function spreads increasingly over larger HCl bond lengths. Thus it explores the region of the barrier saddle point and the deep insertion well. Although also the charge-transfer contribution increases with upsilon, the reaction probability for resonances of the upsilon=2 manifold, which are well above the reaction threshold, is still negligible. This explains the relatively long lifetimes of these upsilon=2 resonances. The reaction probability becomes significant at upsilon=3. Our simulations have shown that an experimental study of this type will allow a gradual spectroscopic probing of the barrier for the reaction.

H-atom abstraction dynamics of reactions between Cl atoms and heterocyclic organic molecules

The HCl(v' = 0, J') rotational state distributions produced in the photoinitiated reactions of ground spin-orbit state Cl(2P3/2) atoms with the organic heterocycles oxirane (c-C2H4O), thiirane (c-C2H4S) and oxetane (c-C3H6O) have been measured using the technique of 2 + 1 resonance-enhanced multiphoton ionization in a time-of-flight mass spectrometer. In contrast to previous studies of H-atom abstraction dynamics by Cl atoms with linear functionalized molecules, the nascent HCl(v' = 0, J') products of the reactions of the three-membered heterocycles oxirane and thiirane are formed rotationally cold, with mean rotational energies <Erot> of (0.28 ± 0.02) kcal mol-1 and (0.31 ± 0.02) kcal mol-1, respectively. The reaction of Cl atoms with the four-membered heterocycle oxetane, however, results in more rotationally excited HCl(v' = 0, J') products for which <Erot> = (0.78 ± 0.03) kcal mol-1. Ab initio calculations were performed at the G2//MP2/6-311G(d,p) level to characterize molecular complexes and transition states on the reactive pathways. In all cases, the reactions were calculated to be barrierless, and weakly bound pre- and post-reaction complexes were located on the potential energy surfaces. The observed distributions and calculated reaction profiles are compared with previous studies of the reactions of Cl atoms with linear functionalized organic molecules and the consequences of the constrained molecular geometry on the HCl(v' = 0, J') rotational distribution discussed in terms of the dipole-dipole interaction model proposed previously.

Efficient Surface Grafting of Luminescent Silicon Quantum Dots by Photoinitiated Hydrosilylation

We suggest a method for efficient (high-coverage) grafting of organic molecules onto photoluminescent silicon nanoparticles. High coverage grafting was enabled by use of a modified etching process that produces a hydrogen-terminated surface on the nanoparticles with very little residual oxygen and by carefully excluding oxygen during the grafting process. It had not previously been possible to produce such a clean H-terminated surface on free silicon nanoparticles or, subsequently, to produce grafted particles without significant surface oxygen. This allowed us to (1) prepare air-stable green-emitting silicon nanoparticles, (2) prepare stable dispersions of grafted silicon nanoparticles in a variety of organic solvents from which particles can readily be precipitated by addition of nonsolvent, dried, and redispersed, (3) separate these nanoparticles by size (and therefore emission color) using conventional chromatographic methods, (4) protect the particles from chemical attack and photoluminescence quenching, and (5) provide functional groups on the particle surface for further derivatization. We also show, using 1H NMR, that the photoinitiated hydrosilylation reaction does not specifically graft the terminal carbon atom to the surface but that attachment at both the first and second atom occurs.

Radical-Mediated Carboxylation of Alkyl Iodides with [11C]Carbon Monoxide in Solvent Mixtures

[reaction: see text] [carboxyl-(11)C]Carboxylic acids were prepared from alkyl iodides via photoinitiated radical reactions using 10(-)(8) mol of [(11)C]carbon monoxide in binary and ternary homogeneous solvent mixtures. Short- (isobutyric), medium-, and long-chain saturated fatty acids (heptadecanoic) were labeled with isolated decay-corrected radiochemical yields ranging from 55% to 70% in 5-7-min reactions. The conversion of [(11)C]carbon monoxide to products reached 80-90%. To obtain good yields in the reactions performed in water-acetonitrile and water-THF mixtures, the addition of tetrabutylammonium hydroxide or potassium hydroxide was essential. The carboxylation was efficient for primary and secondary alkyl iodides. The carboxylation of tertiary iodides was feasible for 1-iodoadamantane but not for tert-butyl iodide. The dependence of the radiochemical yields on reaction time, photoirradiation conditions, and organic and inorganic additives was studied. The method provides a one-step route to [carboxyl-(11)C]carboxylic acids; traditional methods, in contrast, would require several steps. For example, using the devised reaction conditions, 3.19 GBq of purified [1-(11)C]1,10-decanedicarboxylic acid (specific radioactivity 188 GBq/mumol) was obtained within 35 min of the end of 10 muAh bombardment. (1-(13)C)4-Phenylbutyric acid was synthesized using ((13)C)carbon monoxide for identifying the labeling position with (1)H and (13)C NMR.

Photoreactive Functionalization of Poly(ethylene terephthalate) Track‐Etched Pore Surfaces with “Smart” Polymer Systems

AbstractSummary: Poly(ethylene terephthalate) (PET) track‐etched membranes with a pore diameter of ca. 700 nm, optionally surface‐functionalized to create a “carboxyl” or “amino” surface, were used for heterogeneous graft copolymerizations. Grafted poly(acrylic acid) acted as a pH responsive, “smart” polymer. To evaluate the surface‐specific initiation of graft copolymerizations unmodified and primary functionalized membranes were systematically combined with three differently charged benzophenone derivatives as photoinitiators, which were adsorbed on the PET surface prior to the reaction. The functionalized membranes thus obtained were characterized for chemical structure and permeability as a function of pH. The pore structure with a narrow size distribution and the resulting high sensitivity of the membrane permeability to the grafting functionalizations made the track‐etched PET membranes a very useful tool for analyzing structure and function of responsive grafted polymer layers. The primary functionalization of the base polymer with a molecular layer of a multifunctional alkylamine (“amino” surface) enhanced the efficiency of the subsequent graft copolymerization via photoinitiated hydrogen abstraction considerably because a high density of well accessible reactive groups had been introduced. The preadsorption of the photoinitiator on the base polymer surface was significantly improved by ionic interactions between the respective functional groups of the surface and the photoinitiator. Such a photoinitiator preadsorption, especially when combined with a reactive layer from the primary functionalization, enabled a very efficient and surface selective functionalization because a better control of grafting density and a reduction of photoinitiated side reactions along with a more efficient use of the photoinitiator were possible.Water permeabilities (pH 2 and pH 7) of unmodified and functionalized PET membranes for identification of optimal synthesis and evaluation conditions.magnified imageWater permeabilities (pH 2 and pH 7) of unmodified and functionalized PET membranes for identification of optimal synthesis and evaluation conditions.

An Efficient Photoinduced Iodoperfluoroalkylation of Carbon—Carbon Unsaturated Compounds with Perfluoroalkyl Iodides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A study on UV-curable adhesives for optical pick-up: I. Photo-initiator effects

Ultraviolet curable optical pick-up adhesive composites composed of acrylic and methacrylic mono-, bi- and trifunctional monomers and two kinds of urethaneacrylate oligomers has been easily prepared by dual planetary mixer. And various fillers, thixotropic agents, antiemission and rheological additives were also used. The free radical photo-initiated polymerization reaction followed with various photo-initiators and its physical and mechanical properties were tested within 30 s of UV-irradiation. In this paper, we studied the influence of the photo-initiators and their mixtures on the polymerization rate of the adhesive compositions were studied. From these results, the mixture Irgacure 184 and Irgacure 819 provides synergic effects of surface and through curing. UV-adhesives of two types were well applied and settled in CD and DVD optical pick-up body at the reliability evaluation of Samsung Electronics’ production lines.

Photoinitiated Reactions of 2,4,6 TCP on Degussa P25 Formulation TiO2: Wavelength-Sensitive Decomposition

The photoinitiated oxidative reactions of 2,4,6 trichlorophenol (2,4,6 TCP) and 2,4,5 trichlorophenol (2,4,5 TCP) are studied on the titania photocatalyst Degussa P25. On this catalyst 2,4,6 TCP is used to confirm two distinct oxidative mechanisms that are triggered at different light-excitation wavelengths. A charge-transfer mechanism occurs at sub-bandgap energies of the photocatalyst leading to a phenoxyl radical product and an oxidative mechanism occurs at the bandgap leading to a semiquinone radical product. The wavelength dependence of these two mechanisms is discussed.

An efficient photoinduced iodoperfluoroalkylation of carbon-carbon unsaturated compounds with perfluoroalkyl iodides.

Dependent on the selection of the light sources employed, the photoinduced iodoperfluoroalkylation of a variety of unsaturated compounds takes place efficiently via a radical mechanism. Upon irradiation with a xenon lamp through Pyrex (hnu >300 nm), terminal alkenes (R-CH=CH2) and alkynes (R-C triple bond CH) undergo iodoperfluoroalkylation with perfluoroalkyl iodides (RF-I) regioselectively, providing R-CH(I)-CH2-RF and R-C(I)=CH-RF, respectively. In the case of terminal allenes (R-CH=C=CH2), the photoinduced iodoperfluoroalkylation occurs selectively at the terminal double bond, giving the corresponding beta-perfluoroalkylated vinylic iodides (R-CH=C(I)-CH2-RF) in good yields. The photoinitiated reaction of vinylcyclopropanes (c-C3H5-C(R)=CH2) with RF-I proceeds via the rearrangement of cyclopropylcarbinyl radical intermediates to the homoallylic radical intermediates, and the corresponding 1,5-iodoperfluoroalkylated products (I-(CH2)2CH=C(R)-CH2-RF) are obtained in high yields. Isocyanides (R-NC), as C-N unsaturated compounds, also undergo the xenon-lamp-irradiated iodoperfluoroalkylation to provide the corresponding 1,1-adducts (R-N=C(I)-RF) in good yields. Furthermore, the present photoinitiation procedure can be applied to the iodotrifluoromethylation of unsaturated compounds, when the xenon-lamp-irradiated reactions are conducted under the refluxing conditions of excess CF3-I.

Photopolymerization of thiol–allyl ether and thiol–acrylate coatings with visible light photosensitive systems

The photoinitiated polymerization reactions of thiol–allyl ether and thiol–acrylate mixtures under visible light in the presence of several visible photoinitiating systems have been investigated. Remarkable high yield of conversions as well as fast rates of polymerization are observed; a photoinitiating system based on Rose Bengal/Ferrocenium salt/hydroperoxide is particularly efficient. The role of a large variety of photoinitiating systems and the mechanisms involved in the initiation step are discussed.

Kν Correlation Analysis. A Quantitative Two-Dimensional IR Correlation Method for Analysis of Rate Processes with Exponential Functions

A modified two-dimensional infrared correlation technique called kν correlation analysis is introduced. In this method, a mathematical asynchronous cross-correlation is performed between a set of N infrared spectra undergoing a dynamic intensity variation against a set of exponential functions that encompass a user-defined range of rate constants. The observed correlation intensities are a function of the rate constant of the exponential function and the spectral frequency. The kν correlation plots reveal the rate relationships between different molecular groups in terms of a quantitative and tangible parameter, k, which is the rate constant of the exponential function used in the correlation. A new parameter, the effective rate constant, keff, is defined as the point of maximum correlation intensity at particular frequencies in the plot of k vs ν. The calculated values of keff represent the relative rates at which the intensities of the spectral bands change during the course of the dynamic experiment. As a result, these keff values are comparable and can be used to assign quantitative rate relationships. By using simulated IR spectra, it was shown that the keff parameter is sensitive to the relative order in which the intensity change occurs, while the size of the correlation peaks gives an indication of the magnitude of the intensity change. Spectral bands whose rate of intensity change varies through a dynamic data set are distinguished by the presence of both positive and negative peaks in the kν correlation plots. We applied the kν correlation analysis method to the time-dependent IR spectra of the photoinitiated polymerization reaction of ethyl 2-cyanoacrylate. Analysis of the keff effective rate constants showed that vibrational modes corresponding to the monomeric and polymeric cyanoacrylate molecules react differently depending on whether an inhibitor is present.

Molecularly imprinted polymer for theophylline retention and molecular recognition properties in capillary electrochromatography

Molecular imprinting of theophylline in poly (methacrylic acid- ethylene dimethacrylate) as CEC stationary phases was synthesized by an in situ photo-initiated polymerization reaction. The effect of electrolyte pH on xanthine derivatives and the stability of MIP column performance were investigated. the relative standard deviation (D RS) of migration time of five consecutive runs on MIP column was in the range of 2.2%–3.1%. The reproducibility of migration time column to column of M(A) was in the range of 3.8%–4.9%. The highest column efficiency was more than 140 000 plates per meter. The MIP capillaries had showed better selective for theophylline, which comparing with the reference column. The urine sample was separated by spiked 5×10−4 mol·L−1 theophylline.