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Differently substituted pyrrole-azo-benzene molecular photoswitches were prepared in a straightforward synthetic way. Their fundamental properties were investigated by XRD analysis, differential scanning calorimetry, thermogravimetric analysis, cyclic voltammetry, UV-Vis absorption spectroscopy, Hyper-Rayleigh Scattering, and NMR spectroscopy; the experimental results were further corroborated by DFT calculations. Thermal robustness, the HOMO/LUMO levels, and the absorption properties were altered mostly by substituting the N-methylpyrrole moiety and further fine-tuned by modifying the benzene substituents. The pyrrole substituent also proved crucial for the second-order non-linear optical (NLO) response as well as the photoswitching performance. Both fast and slow molecular switches can be designed with the half-life of the (Z) -isomer ranging from 48 seconds to 23.28 hours and the E/Z molar ratio up to 12/88. This comprehensive study allowed elucidation of the fundamental structure-property relationships and subsequently addresses the key aspects of the property tuning via substitution in molecular azo-photoswitches., (© 2024 Wiley-VCH GmbH.)

Tripodal push-pull chromophores with D-(π-A) 3 arrangement were synthesized using 1-methyl-2,4,5-triphenyl-1 H -imidazole as a central electron donor, and their thermal, electrochemical, photophysical and non-linear optical properties were studied and corroborated with quantum-chemical calculations. Their facile synthesis involved Suzuki-Miyaura and Knoevenagel reactions, allowing the installation of various peripheral electron acceptors such as formyl, cyano, ester, trifluoromethyl and more complex moieties such as malonic/acetic acid derivatives, indan-1,3-dione and rhodanine. All phenyl rings appended at the central imidazole core were more or less twisted depending on the peripheral substitution. Although imidazole undergoes reversible one-electron oxidation, peripheral acceptors are reduced irreversibly in a multi-electron process. This behaviour is further seen as a variation of the LUMO, while the HOMO remained almost unaltered across the whole series. TD-DFT calculations revealed centrifugal charge transfer from the central imidazole to all C2, C4 and C5 branches occupied by the LUMO, LUMO+1 and LUMO+2. The HOMO-LUMO gap is tuneable within the range of 3.55-2.31 eV, while the longest-wavelength absorption/emission maxima were found within the broad range of 304-448/393-612 nm. Although the absorption spectra are solvent-independent, the emission depends strongly on the solvent polarity and the electron-withdrawing power of the peripheral acceptors. Extended chromophores with complex electron acceptors were investigated as two-photon absorbers, revealing relatively good cross-section values of up to 521 GM and a figure-of-merit ( Φ F × δ 2PA ) of around 190 GM.

Nine chromophores with ferrocene donor and pyridine/pyridinium acceptors have been prepared and further investigated. The performed X-ray analysis showed partially polarized and geometrically oblate pyridine unit. An extension of the π-system and N -quaternization were revealed as suitable tools for exclusive manipulation of the LUMO with the almost steady HOMO. Whereas the electrochemical HOMO-LUMO gap can be tuned from 3.01 to 1.49 eV, the high- and low-energy absorption bands were found within the range of 280-402/456-547 nm. The pyridinium chromophores showed distinct negative solvatochromism. A thorough DFT analysis has been performed; it turned out that ferrocene donor is capable of two principal D-A interactions, whose employment depends on the appended electron-withdrawing moiety., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Six pyrimidine-based push-pull systems substituted at positions C2 and C4/6 with phenylacridan and styryl moieties, employing methoxy or N,N-diphenylamino donors, have been designed and synthesized through cross-coupling and Knoevenagel reactions. X-ray analysis confirmed that the molecular structure featured the acridan moiety arranged perpendicularly to the residual π system. Photophysical studies revealed significant differences between the methoxy and N,N-diphenylamino chromophores. Solvatochromic studies revealed that the methoxy derivatives showed dual emission in polar solvents. Time-resolved spectroscopy revealed that the higher energy band involved very fast (<80 ps) fluorescence, whereas the lower energy one included long components (≈30 ns) due to long-lived intramolecular charge-transfer fluorescence. In contrast to N,N-diphenylamino chromophores, the methoxy derivatives also showed aggregation-induced emission in mixtures of THF/water, as well as dual emission in thin films, covering almost the whole visible spectrum with corresponding chromaticity coordinates not far from that of pure white light. These properties render the methoxy derivatives as very promising organic materials for white organic light-emitting diodes., (© 2020 Wiley-VCH GmbH.)

A series of new push-pull chromophores based on a combined cyclopenta[c]thiophene-4,6-dione (ThDione) acceptor, N,N-dimethylaniline, N-piperidinylthiophene or ferrocene donors, and ethylene or buta-1,3-dienylene π-linkers has been designed and synthesized. Utilizing one or two ThDione acceptors afforded linear or branched push-pull molecules. Experimental and theoretical study of their fundamental properties revealed thermal robustness up to 260 °C, a electrochemical/optical HOMO-LUMO gap that is tunable within the range of 1.47-2.19/1.99-2.39 eV, and thorough elucidation of structure-property relationships. Compared to currently available portfolio of heterocyclic electron-withdrawing units, ThDione proved to be a powerful and versatile acceptor unit. It imparts significant intramolecular charge transfer and polarizes the π-system, which results in enhanced (non)linear optical response., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

As an extension of the successful dicyanopyrazine photoredox catalysts, a series of X-shaped push-pull molecules with a systematically altered structure were designed and facilely synthesized; their structure-property relationship was elucidated in detail via experimental as well as theoretical calculations. Dicyanopyrazines are proven to be powerful photoredox catalysts with a push-pull arrangement that allows facile property tuning by interchanging a particular part of the D-π-A system. Changing the mutual position of the cyano acceptors and the methoxy, methylthio and thienyl donors as well as modifying the linker allowed wide tuning of the fundamental properties of the catalysts. Contrary to the currently available organic photoredox catalysts, we provided a series of catalysts based on a pyrazine heterocyclic scaffold with easy synthesis and further modification, diverse photoredox characteristics and wide application potential across modern photoredox transformations. The photoredox catalytic activities of the target catalysts were examined in a benchmark cross-dehydrogenative coupling and novel and challenging annulation reactions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Fourteen new D-π-A push-pull chromophores based on two isomeric thienothiophene donors and seven acceptors of various electronic natures have been designed and conveniently synthesized. In contrast to known thienothiophene push-pull molecules, the prepared small chromophores proved to be organic materials with easily tunable thermal, electrochemical and (non)linear optical properties. It has also been shown that small structural variation may result in significantly improved/varied fundamental properties. Very detailed structure-property relationships were elucidated within the systematically developed series of push-pull molecules, which may serve as a useful guide in designing new D-π-A molecules based on fused thiophene scaffolds.

The synthesis of a series of 20 new 2,4,6-tristyrylpyrimidines and three new 2,4-distyrylpyrimidines by means of combination of Knoevenagel condensation and Suzuki-Miyaura cross-coupling reaction is reported. This methodology enables us to obtain chromophores with identical or different substituent on each arm. The photophysical properties of the compounds are described. Optical properties and time-dependent density functional theory calculations indicate that photophysical properties of target compounds are mainly affected by the nature of the electron-donating group in C4/C6 positions, except when the C2 substituent is a significantly stronger electron-donating group. However, the C2 substituent has a strong influence on emission quantum yield: addition of a strong electron-donating group tends to decrease the fluorescence quantum yield, whereas a moderate electron-withdrawing group results in a significant increase of fluorescence quantum yield.

Nine new quadrupolar chromophores based on diketopyrrolopyrrole were designed and prepared by cross-coupling reactions. The property tuning has been achieved by structural variation of the peripheral substituents (donor) and enlargement of the π-system. Fundamental properties of target molecules were studied by differential scanning calorimetry, electrochemistry, and absorption and emission spectra. Nonlinear optical properties were studied by measuring the third harmonic generation. The experimental data were completed by quantum-chemical calculations and structure-property relationships were elucidated.

The synthesis of a series of push-pull derivatives bearing triphenylamine electron-donating group, cyclopenta[c]thiophen-4,6-dione electron acceptor and various π-linkers including (hetero)aromatic fragments is reported. All target chromophores with systematically varied π-linker structure were further investigated by electrochemistry, absorption measurements, and EFISH experiments in conjunction with DFT calculations. Based on electrochemical and photophysical measurements, when a polarizable 2,5-thienylene moiety is embedded into the chromophore π-backbone the highest intramolecular charge transfer (ICT) is observed. Benzene, pyrimidine, and pyridazine derivatives exhibit lower polarizability and extent of the ICT across these π-linkers. The elongation of the π-conjugated system via additional ethenylene linker results in a significant reduction of the HOMO-LUMO gap and an enhancement of the NLO response. Whereas it does not significantly influence electrochemical and linear optical properties, the orientation of the pyrimidine ring seems to be a key parameter on the μβ value due to significant variation of the dipolar moment (μ) value. In 2a and 2c, pyrimidine is oriented to behave as an acceptor and thus generate dipolar molecule with μ above 5 D, whereas in 2b and 2d ground state dipole moment is significantly reduced. This study seems to indicate a high aromaticity of pyrimidine and pyridazine derivatives, close to the benzene analogues and significantly higher than thiophene analogues.

Two new intercalates of tris[4-(pyridin-4-yl)phenyl]amine (TPPA) with zirconium hydrogen phosphate and zirconium 4-sulfophenylphosphonate having formulae Zr(HPO4)2·0.21(C33H24N4)·2.5H2O and Zr(HO3SC6H4PO3)(1.3)(C6H5PO3)(0.7)·0.35(C33H24N4)·2.5H2O were prepared and characterized by thermogravimetry, IR spectroscopy, and powder X-ray diffraction. The TPPA molecule has been selected as a model tripodal push-pull system with three peripheral basic centers that may undergo protonation. Their protonation/quaternization afforded HTPPA/MeTPPA molecules with enhanced intramolecular charge-transfer (ICT), which has been documented by electrochemical measurements, UV-Vis spectra and calculated properties such as the HOMO/LUMO levels and the first and second hyperpolarizabilities. Intercalation of TPPA into layered zirconium hydrogen phosphate and zirconium 4-sulfophenylphosphonate led to its significant organization and protonation as shown by the IR spectra. From the powder X-ray data we can deduce that the TPPA molecules are placed in the interlayer space of both hosts by anchoring two peripheral nitrogen atoms to one host layer and the opposite pyridine-4-yl terminus to the other neighboring host layer. In zirconium 4-sulfophenylphosphonate, the TPPA molecules are oriented perpendicularly, while in zirconium phosphate these molecules are slanted with respect to the layers of the host. On dehydration by heating, the interlayer distance of the intercalate decreases, which indicates a further slanting of the TPPA molecules. It follows from the UV-Vis spectra that TPPA is present in both intercalates in an equilibrium of protonated and non-protonated forms. The described materials represent the first case when a tripodal push-pull system was incorporated into a system with restricted geometry with the aim to influence its optical properties.

Eleven new, stable, push-pull systems that feature 4,5-bis[4-(N,N-dimethylamino)phenyl]imidazole and 4,5-dicyanoimidazole as the donor and acceptor moieties and the systematically extended and varied π-linker were prepared and investigated. Evaluation of the measured UV/Vis spectra, electrochemical data (cyclic voltammetry (CV), rotating-disc voltammetry (RDV), and polarography) and calculated β and γ polarizabilities showed efficient charge transfer (CT) in biimidazole-type chromophores. Push-pull system 27, which features a planar thiophene-derived π-linker, was revealed to be the most efficient chromophore within the studied series. This chromophore possessed the most bathochromically shifted CT band, the lowest electrochemical gap, and highest β and γ polarizabilities. The CT transition was most significantly affected by structural features such as π-linker length, planarity, conjugating arrangement, and the presence of olefinic/acetylenic or 1,4-phenylene/thiophene subunits in the π-linker., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A set of 1160 minimum inhibitory concentration (MIC) values evaluating effect of substitution on the antimycobacterial activity of the previously published 2-(substituted benzyl)sulfanyl benzimidazoles, benzoxazoles, and benzothiazoles has been analyzed by the methods of multidimensional analysis (exploratory analysis, 2D-nonlinear mapping (NLM), principal component analysis (PCA), factor analysis (FA), multiple linear regression (MLR)). The antimycobacterial activity of 2-(subst. benzyl)sulfanyl derivatives of benzimidazole (BIM), 5-methylbenzimidazole (5-Me-BIM), benzoxazole (BOZ), and benzothiazole (BTZ) increased in the order of BTZ

Twelve new imidazole-based potential bi- and tridentate ligands were synthesized and characterized. Whereas in the first series the alpha-amino acid and imidazole moieties were linked by an amino bond, in the second series the tridentate ligands, containing two imidazole groups, were separated by an amide bond. The first series was obtained by the reductive amination of 2-phenylimidazole-4-carboxaldehyde with alpha-amino acid esters. The tridentate ligands were prepared from 2-phenylimidazole-4-carboxylic acid and chiral amines. In the Henry reaction, the amines were revealed as a more reactive species than the less nucleophilic amides, however the enantiomeric excesses were generally poor.