Paula Bosch

Design and Synthesis of Highly Photostable Yellow–Green Emitting 1,8-Naphthalimides as Fluorescent Sensors for Metal Cations and Protons

Two highly photostable yellow–green emitting 1,8-naphthalimides 5 and 6, containing both N-linked hindered amine moiety and a secondary or tertiary cation receptor, were synthesized for the first time. Novel compounds were configured as “fluorophore–spacer–receptor” systems based on photoinduced electron transfer. Photophysical characteristics of the dyes were investigated in DMF and water/DMF (4:1, v/v) solution. The ability of the new compounds to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions (Cu2+, Pb2+, Zn2+, Ni2+, Co2+) and protons. The presence of metal ions and protons was found to disallow a photoinduced electron transfer leading to an enhancement in the dye fluorescence intensity. Compound 5, containing secondary amine receptor, displayed a good sensor activity towards metal ions and protons. However the sensor activity of dye 6, containing a tertiary amine receptor and a shorter hydrocarbon spacer, was substantially higher. The results obtained indicate the potential of the novel compounds as highly photostable and efficient “off–on” pH switchers and fluorescent detectors for metal ions with pronounced selectivity towards Cu2+ ions.

Photopolymerization of hydroxyethylmethacrylate in the formation of organic–inorganic hybrid sol–gel matrices

Hydroxyethylmethacrylate (HEMA) monomer in different contents was used in the preparation of transparent organic-inorganic hybrid sol-gel matrices. The matrices were studied by analytical techniques before and after irradiation. An increase in the homogeneity of the composite material after the irradiation of HEMA, and a chemical linkage of the monomer with the surface has been observed. Photopolymerization processes were studied by differential scanning calorimetry (DSC). Details of the irradiation times, polymerization rates, and DSC related parameters of HEMA in the sol-gel matrices are reported.

Sorption and diffusion of organic solvents through photo-crosslinked SBS block copolymers

Abstract Styrene-butadiene-styrene (SBS) block copolymer exposed to UV radiation in the presence of unimolecular and bimolecular photoinitiators yields a crosslinked polymer. When 2,2-dimethoxy-2-phenylacetophenone is used as photoinitiator the photocrosslinking takes place fundamentally through the addition of the benzoyl and/or dimethoxyphenyl radicals to the double bonds (cis, trans and vinyl) of the SBS block copolymer. The reactivity of the radicals towards the three double bonds is as follows: vinyl > cis > trans. Diffusion and sorption of chloroform and toluene through SBS block copolymer have been studied in the temperature interval of 25–60°C by conventional weight gain experiments. The diffusion results have been analyzed in terms of the simple Fickian model. Diffusion of toluene and chloroform in crosslinked SBS block copolymer was found to deviate slightly from the normal Fickian character which was attributed to the diphasic morphology of the SBS copolymer. The approach to a normal Fickian behaviour as the temperature and crosslinking increase has been explained considering the decrease in the degree of completion of the microphase separation with the increase of both the crosslinking and temperature. Temperature was found to activate the diffusion process, which was supported by higher intrinsic diffusion coefficient values and slopes values at higher temperatures. Entropy and enthalpy of sorption were estimated by using the Van’t Hoff relationship. Crosslinked SBS block copolymer–solvent interaction parameter χ were computed using the Flory–Rehner equation. The χ parameter (0.40 and 0.41 for chloroform and toluene, respectively) indicated strong polymer–solvent interaction. The crosslinking densities of the SBS block copolymer irradiated were relatively low ( M c values go from 23,000 for an irradiation time of 30 min until 5000 for an irradiation time of 120 min).

New fluorescent probes for monitoring polymerisation reactions: 1. Synthesis, solvatochromism and emission properties

Abstract The synthesis of three new highly fluorescent compounds is reported and the basic spectroscopic properties of them described, discussed and compared with those of some structurally related fluorescent compounds usually used as fluorescent probes. The effect of the solvent on ambient temperature absorption and fluorescence spectra, and the solvatochromic properties observed for both ground and first excited states of all the probes were used to evaluate their first excited dipole moments using the solvatochromic shift method (Bakhshiev’s correlation).

Microfluidic approaches for the fabrication of gradient crosslinked networks based on poly(ethylene glycol) and hyperbranched polymers for manipulation of cell interactions

High-throughput methods allow rapid examination of parameter space to characterize materials and develop new polymeric formulations for biomaterials applications. One limitation is the difficulty of preparing libraries and performing high-throughput screening with conventional instrumentation and sample preparation. Here, we describe the fabrication of substrate materials with controlled gradients in composition by a rapid method of micromixing followed by a photopolymerization reaction. Specifically, poly(ethylene glycol) dimethacrylate was copolymerized with a hyperbranched multimethacrylate (P1000MA or H30MA) in a gradient manner. The extent of methacrylate conversion and the final network composition were determined by near-infrared spectroscopy, and mechanical properties were measured by nanoindentation. A relationship was observed between the elastic modulus and network crosslinking density. Roughness and hydrophilicity were increased on surfaces with a higher concentration of P1000MA. These results likely relate to a phase segregation process of the hyperbranched macromer that occurs during the photopolymerization reaction. On the other hand, the decrease in the final conversion in H30MA polymerization reactions was attributed to the lower termination rate as a consequence of the softening of the network. Valvular interstitial cell attachment was evaluated on these gradient substrates as a demonstration of studying cell morphology as a function of the local substrate properties. Data revealed that the presence of P1000MA affects cell–material interaction with a higher number of adhered cells and more cell spreading on gradient regions with a higher content of the multifunctional crosslinker.

New Fluorescent Probes for Monitoring Polymerization Reactions: Photocuring of Acrylic Adhesives, 2

The results of following the fluorescence of selected probes during the entire range of curing of acrylic-based adhesives are presented in this work. The change of fluorescence parameters has been continuously measured during the photocrosslinking reactions of acrylic adhesive systems under UV-irradiation. Real-time FT-IR (RT-FT-IR) has been used to measure the conversion reached at different irradiation times. Intensity ratio, maximum emission wavelength and the first moment of fluorescence have been used as parameters to correlate with the double bond conversion degree. Two-slope plots have been obtained during UV-curing, which correspond to the different stages of the crosslinking reaction. Also, the size of fluorescent probe appears to be a parameter that influences the sensing time in which the probe can detect the changes in viscosity/polarity occurring along the UV-curing process. The results are compared with those of commercial probes such as dansylamide and pro- dan. The use of the fluorescence technique allowed us to understand the mechanism taking place and the role of the binder matrix, depending on the photoinitiator used. This information is not obtained when the reaction is followed by the conventional RT-FT-IR technique.

Photochemistry and photoinitiator properties of novel 1-chloro-substituted thioxanthones. III: Preliminary study of the photoacid generation

The dehalogenation of a selected number of 1-chloro-4-acyloxy/oxy derivatives of thioxanthone have been studied by a spectrophotometric method, developed using the sodium salt of tetrabromophenol blue as the acid probe. The method has allowed the in situ monitoring of the photoacid generation by absorption spectroscopy. This has consequently lead to the evaluation of absolute quantum yields of acid generation through steady state photolysis, and the investigation of the derivatives as potential photoacid generators, able to initiate cationic polymerisation of cyclohexene oxide.

New fluorescent probes for monitoring the polymerization reaction: p-vinyliden derivatives of N,N-dimethylaminoaryl compounds

The fluorescence emission of two new fluorescent probes have been studied in environments of different polarity and viscosity. The probes have been shown to be sensitive to changes in both microviscosity and micropolarity of the surroundings, and their dipolar moments in the excited state have been estimated. They have been used as fluorescent sensors to monitor the photopolymerization reactions of some mono- and di-functional (meth)acrylate monomers, and two commercial photocurable acrylic adhesives. The fluorescence emission band of the probes showed an increase in intensity as the degree of conversion increases, throughout the entire polymerization range in the different systems checked. Their sensitivity have been compared with that of their parent compound N,N-dimethylamino-bencilidenenmalononitrile.

Kinetic investigations on the photopolymerization of di‐ and tetrafunctional methacrylic monomers in polymeric matrices. ESR and calorimetric studies. II. Postpolymerization reactions

The reaction kinetics in the dark of photopolymerized mono- and dimethacrylates in a polymeric binder has been studied. Electron spin resonance spectroscopy (ESR) provided useful information regarding the nature of the radicals involved in postpolymerization reactions. Computer simulations were performed to study the decay of the propagating radicals by considering normal bimolecular termination and transfer reactions of the radicals to the binder. Differences were found in the termination reactions for mono- and difunctional monomers when they were photopolymerized in a solid medium. Absolute kinetic constants for H-transfer reaction with the binder, relative kinetic rate constants for radical-radical coupling, and average lifetimes for the radicals have been calculated.

Kinetic investigations on the photopolymerization of di- and tetrafunctional (meth)acrylic monomers in polymeric matrices. ESR and calorimetric studies. I. Reactions under irradiation

The photopolymerization of several di- and tetrafunctional (meth)acrylic monomers in the presence of a styrene–butadiene–styrene polymeric matrix (SBS) has been studied. Electron spin resonance spectroscopy (ESR) and differential scanning photocalorimetry (photo-DSC) were used as monitoring techniques to identify the photogenerated radicals and analyze photopolymerization profiles, radical environments, and radical secondary reactions. The study of the photopolymerization and/or photocrosslinking reactions of these monomers in the solid media was carried out by taking into consideration different factors, such as the influence of both monomer and photoinitiator structures on the hydrogen abstraction in the binder with formation of benzylic and allylic radicals, the polymerization of the monomers itself and the hydrogen abstraction reaction in the polymerized acrylic chains. Finally, irradiation of the system SBS/photoinitiator in the absence of monomer was also accomplished.