Development of new dyeing photoinitiators based on benzylideneimidazopyridine dyes

Several dyes containing benzylideneimidazopyridine moiety (BIPDs) were synthesized and evaluated as photoinitiators for free‐radical polymerization induced with the visible emission of an argon‐ion laser. One method of dye structure change was applied in our study. The modification was based on the character of the substituent introduced into both the imidazopyridine skeleton and phenyl ring. Several different groups were tested including heavy atoms (? CI, ? Br) as well as electron‐accepting (? NO₂), and electron‐donating groups [? N(CH₃)₂, ? OCH₃]. Analysis of the dye properties demonstrated that there is a significant heavy atom effect on the photoinitiation ability of the novel dyes in both cases, for example, when a heavy atom is introduced into the phenyl ring as well as into the imidazopyridine part of the molecule. The introduction of an electron‐acceptor or electron‐donor group into the phenyl part of the dye caused a dramatic decrease in its photosensitivity. The type of applied counterion had no effect on the overall sensitivity of a dye. BIPDs are not particularly good photoinitiators. Further modification of the dye structure involved the elimination of the motion of a C?C bond by the coplanarization of the styrylium residue with other parts of the dye. This approach decreased the degree of branching of the dye, which stabilized the molecule in its excited state. The formed dye, quinoline[2,3‐b]‐2,3‐dihydro‐1H‐imidazo[1,2‐a]pyridinium bromide (QDIPB), exhibited dramatically enhanced sensitivity. QDIPB possessed broad structured spectra with a long‐wavelength part shifted to the blue as compared to other BIPD dyes. The change of the absorption spectra and its high photoinitiation ability makes QDIPB a good candidate for the photoinitiating system applied in dental restorative materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3048–3055, 2003     

Stability of transverse vibration of a circular plate subjected to a periodically varying torque

The paper is concerned with transverse vibration of a circular plate subjected to periodically varying torsion. The instability regions are found and plotted for the plate under a tangent uniform load and a tangent concentrated force.     

N‐methylpicolinium derivatives as the coinitiators in photoinitiating systems for vinyl monomers polymerization

Five N‐methylpicolinium derivatives were investigated to test their abilities to function as second coinitiators in free radical photopolymerization initiated by N,N′‐diethylcarbocyanine—n‐butyltriphenylborate photoredox pair ( P19B2 ). As it is shown by the kinetic data, an addition of picolinium derivatives into P19B2 photoinitiating system visibly increases the efficiency of photoinitiation. The results suggest that the rates of photoinitiation depend on the rate of the picolyl radicals formation. The redox potentials of tested N‐methylpicolinium derivatives were measured and the calculation of free energy change for the possible electron transfer reactions between all components of the system (both stable and transient individuals) was performed. The results suggest that cyanine dyes are able to start a specific chain of an electron transfer reactions involving different coinitiators (borate salt and N‐alkylpicolinium derivatives), giving as a result one photon—two‐radicals photochemical response. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 576–588, 2009     

Spectroscopic properties of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate

The luminescence properties of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate (EAADCy) have been studied using steady-state, time-resolved spectroscopic techniques, electrochemical measurements and semiempirical calculations. A series of photophysical measurements and quantum-chemical calculations were carried out with EAADCy in search of an evidence of the occurrence of the aniline group rotation. Studies in different solvents, as well as semiempirical calculations, indicate that conformations with donor and acceptor groups coplanar absorb and emit at wavelengths that are longer than those observed for donor–acceptor groups oriented orthogonally. The values of the dipole moments of planar and perpendicular form of molecule under study were estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the solvent dielectric constant and refractive index. Experimentally calculated changes of the dipole moment values are in fair agreement with semiempirical computational predictions.     

Nonstationary Stokes system in anisotropic Sobolev spaces

The nonstationary Stokes system with slip boundary conditions is considered in a bounded domain . We prove the existence and uniqueness of solutions to the problem in anisotropic Sobolev spaces . Thanks to the slip boundary conditions, the Stokes problem is transformed to the Poisson and the heat equation. In this way, difficult calculations that must be performed in considerations of boundary value problems for the Stokes system are avoided. This approach does not work for the Dirichlet and the Neumann boundary conditions. Because solvability of the Poisson and the heat equation is carried out by the regularizer technique, we have that σ > 3,α > 0. Copyright © 2014 John Wiley & Sons, Ltd.     

New heterobicationic hemicyanine dyes: Synthesis,spectroscopic properties,and photoinitiating ability

This article describes the synthesis, spectroscopic properties, and free‐radical photoinitiation ability of new heterobicationic hemicyanine dyes. A new synthetic strategy for the preparation of unsymmetrical cyanine dyes has been developed, based on 2‐methylbenzothiazole derivative quaternization by 3‐pyridinium‐1‐bromopropane bromide and subsequent condensation of the resulting product with p‐(N,N‐dimethylamino)benzaldehyde. The tested dyes possess in one molecule two quaternary nitrogen atoms; that is, they are heterobicationic in nature. Novel hemicyanine dyes have been tested as visible‐light photoinitiators of vinyl monomer polymerization. Heterobicationic hemicyanine dyes paired with n‐butyltriphenylborate anions are very efficient photoinitiators of the free‐radical polymerization of trimethylolpropane triacrylate when irradiated with the visible emission of an argon‐ion laser. The photoinitiating abilities of the novel photoredox pairs are compared with the photoinitiation properties of their monocationic equivalent {3‐methyl‐2‐[4‐(N,N‐dimethylamino)styryl]benzothiazolium n‐butyltriphenylborate} as well as a Rose Bengal derivative (a typical triplet‐state photoinitiator). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6345–6359, 2006     

Stilbene-Like Molecules as Fluorescent Probes Applied for Monitoring of Polymerization Process

2-(p-N,N-dimethylaminostyryl)benzoxazole (OS), 2-(p-N,N-dimethylaminostyryl)-benzothiazole (SS) and 2-(p-N,N-dimethylaminostyryl)naphtiazole (PS) were prepared and their absorption and fluorescence spectra were measured in various solvents at room temperature. On the basis of the solvatochromic behavior the ground state (μ_g) and excited state (μ_e) dipole moments of these pN,N-dimethylaminostyryl derivatives were evaluated. The dipole moments (μ_g and μ_e) were estimated from solvatochromic shifts of absorption and fluorescence spectra as function of the dielectric constant (ɛ) and refractive index (n) of applied solvents. The absorption spectra only slightly are affected by the solvent polarity in contrast to the fluorescence spectra that are highly solvatochromic and display a large Stokes shift. The analysis of the solvatochromic behavior of the fluorescence spectra as function of Δf (ɛ, n) revealed that the emission occurs from a high polarity excited state. The large dipole moment change along with the strongly red-shifted fluorescence, as the solvent polarity is increased, demonstrate the formation of an intramolecular charge transfer state (ICT). Compounds under the study were used as fluorescence probes for monitoring the kinetics of polymerization. The study on the changes in fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate (MMA) and during photoinitiated polymerization of 2-ethyl-2-(hydroxymethyl)propane-1,3-diol triacrylate (TMPTA).     

Magnetism of ErAgSn studied by 119Sn Mössbauer spectroscopy

Antiferromagnetic ErAgSn compound was investigated in detail by ¹¹⁹Sn Mössbauer spectroscopy in a temperature range between 2.2 and 300 K. The ¹¹⁹Sn spectra recorded below 4.2 K can be well fitted with a single main magnetic component in agreement with recent neutron diffraction studies [1]. A broad distribution of magnetic hyperfine fields observed above 4.2 K and enhanced spin correlations among Er³⁺ ions at T > T _N = 5.6 K are the remarkable features of the investigated system.