Beata Koszarna

Photophysical characterization of free-base corroles, promising chromophores for light energy conversion and singlet oxygen generation

A detailed photophysical characterization of a series of six free-base corroles with different substitution patterns at meso-positions is presented. In air-free toluene at 295 K, the luminescence quantum yields range from 0.13 to 0.22 and lifetimes vary from 4.1 ns to 6.3 ns whereas in air-saturated toluene the lifetimes range from 3.8 ns to 5.6 ns. In glassy toluene at 77 K the lifetimes have values in the range 5.2 ns to 7.9 ns. Transient absorption spectra of the singlet excited states have positive bands art λ 680–700 nm. The transient absorption spectra of the lowest triplet display a band around 460–470 nm and bleaching features in the Q bands region, no absorption above 700 nm. The triplet lifetimes in air-free toluene are in the interval 50–150 μs. The lowest excited states react with oxygen and sensitized singlet oxygen (1Δg) yields of 0.51–0.77 are determined via its luminescence. Electron and energy transfer from the excited states to molecular oxygen is discussed. Effect of polar solvents on the luminescence parameters indicate that charge transfer (CT) excited states play a very minor role. Thermal and photo stability is excellent for most of the examined compounds in toluene and dichloromethane.

Palladium-catalyzed 2-arylation of pyrroles.

A methodology that affords N-alkyl-2-arylpyrroles and N-aryl-2-arylpyrroles via direct coupling from aryl iodides has been developed. After examining various reaction parameters: solvent, ratio of reagents, catalyst, base and additives the optimal conditions for the condensation were identified. Two crucial factors, (a) anhydrous DMSO as solvent and (b) 5 M excess of pyrrole counterpart, were found to strongly influence the reaction outcome. The conditions identified (PdCl(2)(PPh(3))(2), AgOAc, anhyd DMSO, KF, 100 degrees C, 5 h) resulted in the formation of 2-arylpyrroles in 14-80% yield. Furthermore, the synthesis is compatible with electron-withdrawing and electron-donating groups on the aryl moiety.

Parallel synthesis of meso-substituted corroles and meso-substituted [22]pentaphyrins(1.1.1.0.0) from diacyl-dipyrromethanes

A new method was devised for the synthesis of 1,9-diacyldipyrromethanes - crucial intermediates in the synthesis of meso-substituted corroles and porphyrins with different substituents. The diacylodipyrromethanes formation involves acylation of dipyrromethanes with salts made in situ from POCl3 and tertiary amides. This modified Vilsmeier approach gives higher yields and no concomitant formation of monoacyldipyrromethanes as compared with the Grignard route. Moreover, compounds possessing groups previously inaccessible (CN, NO2 etc.) can be synthesized. During optimization of the transformation of diacyldipyrromethanes into meso-substituted corroles it was found that if macrocyclization reaction mediated by DDQ is performed in the presence of large excess of pyrrole, meso-substituted [22]pentaphyrins(1.1.1.0.0) can be obtained in moderate yield. The currently described procedure constitutes a new method for the synthesis of these valuable porphyrinoids. Corroles possessing interesting, easy to transform, functional groups were obtained in 3-40% yield.

Insights into the Tautomerism in meso‐Substituted Corroles: A Variable‐Temperature 1H, 13C, 15N, and 19F NMR Spectroscopy Study

Tris(pentafluorophenyl)corrole and its (15)N-enriched isotopomer were studied in [D8]toluene solution by 1D and 2D variable-temperature NMR techniques to establish the mechanisms of tautomerization of the NH protons inside the interior of the corrole macrocycle. Three such rate processes could be identified of which two modulate the spectral line shapes at temperatures above 205 K and the third is NMR-inaccessible as it is very fast. The latter involves the proton engaged in an unsymmetrical proton sponge unit formed by two pyrrole nitrogen atoms. Temperature and concentration dependences of the two remaining processes were determined. One of them is purely intramolecular and the other is intermolecular at low temperatures, with growing contribution of an intramolecular mechanism at elevated temperatures. The proposed microscopic mechanisms of all these processes are semi-quantitatively confirmed by quantum chemical calculations using density functional theory.

Synthesis of trans-A2B2-porphyrins bearing phenylethynyl substituents.

Efficient and convenient conditions for the preparation of trans-A(2)B(2)-porphyrins bearing two phenylethynyl moieties directly from phenylpropargyl aldehydes and dipyrromethanes of diversified lipophilicity and reactivity have been developed. This new procedure allows the preparation of a library of porphyrins of this architecture with a wide range of substituents. Thanks to the identification of the reagent solubility as one of the key factors influencing the yield of the porphyrinogens, we were able to improve yields to ca. 30%. The scope and limitations of two sets of conditions have been explored. The methodological advantage of this approach is its straightforward access to building blocks and the formation of the porphyrin core in the last step without the need for deprotection of the triple bond or bromination and consecutive coupling reaction, which often demands copper salts to proceed smoothly, especially with electron-deficient alkyne partners. Therefore, it prevents undesired copper porphyrin formation, as well as the need for utilizing expensive alkynes. A two-step method for the preparation of phenylpropargyl aldehydes has also been refined.

Biscoumarin-containing acenes as stable organic semiconductors for photocatalytic oxygen reduction to hydrogen peroxide

Conversion of solar energy into chemical energy in the form of hydrogen peroxide and other reactive oxygen species has been predicted to be an efficient strategy, yet few organic materials systems ...

The impact of interplay between electronic and steric effects on the synthesis and the linear and non-linear optical properties of diketopyrrolopyrrole bearing benzofuran moieties

An in-depth investigation of the reaction of substituted salicylaldehydes with chloroacetonitrile led to the development of new conditions for the synthesis of 2-cyanobenzofurans. The crucial improvement lies in the use of phase-transfer catalysis in the second step, i.e., intramolecular aldol type condensation. In a two-step process, the reactants were transformed into a library of 3,6-bis(benzofuran-2-yl)diketopyrrolopyrroles. We show that the presence of a methyl group in a position adjacent to the cyano functionality only slightly decreased the yield of diketopyrrolopyrroles (to 30–57%). An analysis of the relationship between the degree of polarization/planarization of aryl-diketopyrrolopyrroles and their one- and two-photon spectroscopic properties is reported. Careful design of the desired dyes and enhanced control of their ability to assume a planar molecular structure resulted in interesting photophysical properties, such as absorption and emission in the so-called biological window. Despite having less promising linear spectroscopic properties, the deplanarized molecules possess pretty strong two-photon absorbing properties. Placing methyl groups at adjacent positions to the linkage between benzofuran and the DPP core caused the formation of yellow-emitting dyes with almost quantitative fluorescence quantum yield, moderate Stokes shift and reasonable two-photon absorption cross-sections.

Two-photon absorption spectroscopy of corroles

We report simultaneous two-photon absorption (2PA) spectra in a series of substituted corroles and related porphyrins in 800-1400 nm laser wavelength range. Compared to the porphyrins, the 2PA spectrum of corroles contains a distinct and relatively high intensity peak, sigma(2) = 60-130 GM, close to twice the wavelength of Soret maximum (800-850 nm). The increase of 2PA peak cross section is explained in terms of decreased symmetry of the contracted macro-cycle, and is most likely related to relaxing of the parity selection rules that restrict 2PA in the Soret band for more symmetrical porphyrins. We also observe that the strength of the 2PA peak in Soret region decreases with the electron-withdrawing ability (increasing Hammett constant) of the side substituents, which can be explained by assuming that the corrole core itself possesses electron-accepting ability. The peak 2PA cross sections in the Q-region are much less than in Soret-region, and can be quantitatively described within the two-level approximation taking into account permanent dipole moments in the ground and excited states.