Agnieszka Bajorek

Developing of fluorescence probes based on stilbazolium salts for monitoring free radical polymerization processes. II.

The series of 1-methyl-4-(4-aminostyryl)pyridinium perchlorates was investigated as fluorescent probes for the monitoring of the free radical polymerization progress. The study on the changes in fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate. The purpose of these studies was to find a relationship between the structure of fluorophore and the changes in their fluorescence shape and intensity observed during the monomer conversion into polymer. The probes under the study during the course of polymerization increase their fluorescence intensity at least one order of magnitude. Such increase qualified the tested probes as good fluorescence probes.

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

Abstract2-(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 (μg) and excited state (μe) dipole moments of these pN,N-dimethylaminostyryl derivatives were evaluated. The dipole moments (μg and μe) 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).

Interaction of carbocyanine dyes with DNA: synthesis and spectroscopic studies.

Six carbocyanine dyes have been synthesized and their interactions with DNA have been investigated for their prospective use as fluorescent markers in molecular biology. The noncovalent binding of the compounds with DNA was explored by fluorescence spectroscopy, ultraviolet/visible spectrophotometry, and photobleaching. The electron-withdrawing ability of the substituents in N-position of free thio- and selenocarbocyanines strongly affected their photostabilities. Changes in the experimental conditions, such as the presence or absence of oxygen, had an impact on the rate of photobleaching. In the presence of DNA, absorbance photofading and fluorescence photobleaching occurred. It appears that the reduction of fluorescence intensity was due to quenching of the dye fluorescence by interaction with DNA.

Experimental and Theoretical Studies of the Spectroscopic Properties of Chalcone Derivatives

Newly synthesized, differently substituted chalcones (1,3-diaryl-2-propen-1-ones) have been studied using steady-state and time-resolved techniques combined with quantum-chemical modelling. To explore spectroscopic structure - property relationships the substituent (acceptor moiety) was chosen according to systematic variation in the Hammett parameter. It was shown that photophysical properties of the studied donor-acceptor (D-A) molecules can be predicted in terms of a simple model from the properties of individual chromophores (composite-model of decoupled moieties: donor (D) and acceptor (A)). The results of spectroscopic measurements also indicate that for investigated D-A fluorophores in medium-polar solvent, the initially populated, locally excited (LE) state (where the fundamental role plays donor moiety (D*-A)) reacts further to produce intramolecular charge transfer (ICT) state. Additionally, the experimental absorption (Mge) and fluorescence (Meg) transition dipole moments were calculated on the basis of spectroscopic data and compared with results of our quantum-chemical calculations. The absorption transition dipole moment was found to vary linearly with the Hammett substituent coefficient (σ).

Convenient Synthesis of p-Aminobenzoic Acids and their Methyl Esters

Amino groups are of significant biological and industrial importance as they are fundamental components of living organisms and of amino acids. The properties of amines depend on the type of substituents on the nitrogen, steric hindrance, and solvation effects. In general, the basicity of an amine increases with the number of alkyl groups on the amine while aryl substituents generally delocalize the lone pair of electrons into the ring leading to decreased basicity. These factors may cause amino groups to have a major influence on the spectroscopic and redox properties of such compounds as well as on the possibility of the occurrence of the interand intramolecular electron transfer (ICT) processes. Aromatic amines are generally quite toxic and readily absorbed through the skin, some are potent carcinogens. However, appropriate modifications of their structure make it possible to access compounds having the desired properties such as desired in biologically active compounds, polymers, radical photo-initiators, dyes, photo-voltaic cells, lightemitting diodes, spectroscopic probes, modern medical techniques and in many other fields. p-Aminobenzaldehydes constitute convenient and frequently used stating reagents for the preparation of various amines. Babu andBalasubramaniam proposed a simplemethod for the synthesis of p-dimethylaminobenzoic acid by oxidation of an aldehyde. However, it requires sodium chlorite, which is hazardous and less universally available.Moreover, this process, like the methods using hydrogen peroxide as oxidant, were only autilized for the preparation of p-dimethylaminobenzoic acid. No evidence of their scope and versatility with respect to other amine derivatives of benzoic acid was provided. Our need of various p-aminobenzoic acids and their esters for the preparation of a few boron-dipyrromethene (BODIPY) dyes, and other dyes containing difluoroborane moiety as spectroscopic probes prompted us to re-investigate and modify the reaction reported by Ott and his group nearly fifty years ago after our unsuccessful attempts to obtain these acids in good yields by oxidation of aldehydes with silver nitrate or via the carboxylation of the corresponding Grignard reagents. We now report this route as a very convenient preparation of these aminobenzoic acids, requiring only the use of simple and readily available reagents. It involves no solvents, and produces the desired acids efficiently and in high purity with no troublesome