Marek Pietrzak

Hemicyanine dyes: synthesis, structure and photophysical properties

Abstract The cationic hemicyanine dyes: 3-ethyl-2-[4-(N,N-dialkylamino)-styryl]-benzoxazolium salts, 2-[4-(N,N-dialkylamino)-styryl]-1-(4-iodobenzyl)pyridinium salts and 2-[4-(N,N-dialkylamino)-styryl]-1-methyl-6-iodopyridinium salts were synthesized and characterized. The dyes were prepared by the condensation of 3-ethyl-2-methylbenzoxazole salts, 1-(4-iodobenzyl)-2-methylpyridinium salts or 1,2-dimethyl-6-iodopyridinium salts with p-(N,N-dialkylamino)benzaldehydes. Three groups of chromophores with the same acceptor group but with various donor groups were obtained. The spectroscopic properties of the prepared dyes were determined in organic solvents.

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.

Spectroscopic and nonlinear optical properties of new chalcone fluorescent probes for bioimaging applications: a theoretical and experimental study

AbstractIn this study, the newly synthesized non-centrosymmetric, 4-dimethylamino-3′-isothiocyanatochalcone (PKA) compound was presented. This compound belongs to the chalcone group, and its main purpose is to be used in biomedical imaging as a fluorescence dye. For this reason, the linear and nonlinear properties in solvents of different polarity were thoroughly studied. In accordance with the requirements for a fluorochrome, the PKA compound is characterized by strong absorption, large Stokes’ shifts, relatively high fluorescence quantum yields and high nonlinear optical response. Moreover, the isothiocyanate reactive probe was conjugated with Concanavalin A. Conventional fluorescence microscopy imaging of Candida albicans cells incubated with the PKA-Concanavalin A, is presented. The results of this study show that the novel conjugate PKA-Concanavalin A could be a promising new probe for cellular labelling in biological and biomedical research. Graphical abstractSpectroscopic behavior of the PKA dye

DEVELOPMENT OF FLUORESCENCE PROBES BASED ON STILBAZOLIUM SALTS FOR MONITORING FREE RADICAL POLYMERIZATION PROCESSES

A series of 1-methyl-2-(4-aminostyryl)pyridinium perchlorates and iodides were investigated as fluorescent probes for the monitoring of the progress of free radical polymerization. The study on the changes in the fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate and during photoinitiated polymerization of a 2-ethyl-2-(hydroxymethyl)propane-1,3-diol triacrylate (TMPTA)–1-methylpyrrolidin-2-one (MP) mixture. The purpose of these studies was to find a relationship between the changes in the shape and intensity of probe fluorescence and degree of monomer conversion into polymer. The polymer formation was estimated gravimetrically or by the measurement of the degree of monomer double bond disappearance using FTIR spectroscopy.

Cyanine borates revisited. Study of the kinetics of photoinitiated free radical polymerization via intermolecular electron transfer process

Three series of cyanine butyl triphenyl borate salts were prepared and tested as initiators of free radical polymerization photoinitiated via the photoinduced electron transfer process. To illustrate the influence of the primary process on the rate of photoinitiated polymerization the fluorescence lifetime of the tested dye containing non-electron donating counterion as well as electron donating borate ion were measured. The fluorescence lifetime measurements were performed using a pico/femtosecond spectrometer allowing a successful analysis of fluorescence decay signals in the range of single picoseconds. As obtained results show, for cyanine dyes bi-exponential decay of fluorescence was observed, while for cyanine with a substituent at the meso position, for the majority of dyes, mono-exponential decays were obtained. Based on fluorescence measurements the rate of the electron transfer process between excited dyes and borate anions was calculated and a short discussion on photophysics of cyanine dyes is given. Several important conclusions arrive from the theoretical and experimental data: (i) the experimental data reveal that the relationship between the rate of the electron transfer and the free energy for this reaction display typical “normal Marcus region” kinetic behavior; (ii) the experimental results show that the relationship between the logarithm of the rate of polymerization and the logarithm of the rate constant for the electron transfer is linear in character. This finding permits the conclusion that the rate of photopolymerization is a function of the free energy change of the electron transfer (ΔGel). This type of relationship is observed only for cyanines with no substituent in the meso position. These observations allow the conclusion that in the case of meso-cyanines the fluorescing state of the dye is not the state that is reduced by the borate. The main conclusion derived from the data presented in the paper is that the Marcus theory of electron transfer can be extended for the description of certain types of photoinitiated polymerization.

Dipole moment determination of 4-[N-(5,6,7,8-tetrahydroisoquinolinium-5-ylidene)methyl]-N,N-dialkylaniline iodides in solution

Electronic absorption and fluorescence spectra of eight hemicyanine dyes were recorded at room temperature in several solvents of different polarity. The spectral data were analyzed using the theory of solvatochromism, based on a dielectric continuum description of the solvent and the classical Onsager cavity model. They were used to evaluate the excited state dipole moment using methods applied by McRae, Lippert, Mataga and Bakhshiev. DFT calculations were carried out to estimate the ground state dipole moment and Onsager cavity radius. The difference in the excited and ground state dipole moments (μe-μg) of the molecule under study is positive. It means that the excited states of the dyes are more polar than the ground state. The increase in dipole moments upon excitation is explained in terms of the nature of the excited state and its resonance structures.

Conformational equilibrium in supramolecular chemistry: Dibutyltriuret case.

Summary The association of substituted benzoates and naphthyridine dianions was used to study the complexation of dibutyltriuret. The title molecule is the simplest molecule able to form two intramolecular hydrogen bonds. The naphthyridine salt was used to break two intramolecular hydrogen bonds at a time while with the use of substituted benzoates the systematic approach to study association was achieved. Both, titrations and variable temperature measurements shed the light on the importance of conformational equilibrium and its influence on association in solution. Moreover, the associates were observed by mass spectrometry. The DFT-based computations for complexes and single bond rotational barriers supports experimental data and helps understanding the properties of multiply hydrogen bonded complexes.

Quantum-chemical calculations of the electronic structure of 2-amino-1,3-dicyano-5,6,7,8-tetrahydronaphthalene derivatives

The UV-Visible absorption spectra of six, newly synthesized donor-substituted 2-amino-1,3-dicyano-5,6,7,8-tetrahydronaphthalene have been measured in methylcyclohexane (MCH) and assigned with the help of quantum-chemical calculations. Our calculations have been performed to assess information regarding the electronic state energy values, corresponding oscillator strengths, x-, y-, z-components of the transition dipole moments and molecular orbitals involved in the main electronic transitions of the studied compounds. Additionally, the experimental absorption transition dipole moments were calculated, on the basis of spectroscopic data, and compared with results of our quantum-chemical calculations. On the basis of the experimental results and quantum-chemical calculations, it was shown that the long-wavelength absorption band involves an overlap of three electronic transitions of different character. For all studied donor-acceptor (D-A) compounds in vapour-phase, the long-wavelength transition (S0→S1) does not possess charge transfer character, whereas the S0→S2 transition possesses electron transfer character e.g., π-electrons of the acceptor moiety are moved to the donor part. Moreover, it is found that the electronic structure of the studied biphenyl derivatives can be approximately described within composite-model of decoupled moieties: donor and acceptor.

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).

Influence of the Nature of the Amino Group in Highly Fluorescent Difluoroborates Exhibiting Intramolecular Charge Transfer

A series of difluoroborates were synthesized from CH acids. All compounds were substituted with dialkylamino groups (NR2). The lone electron pair of the nitrogen atom of this donor moiety is variably delocalized toward the difluoroborate core that acts as the electron acceptor. This was rationalized in light of the various geometries of the amino group. The degree of charge transfer was quantified on the basis of the results of time-dependent density functional theory calculations.