The study demonstrates the influence of ethanol as a stabilizer in chloroform on the thermal cis-trans isomerization kinetics of photochromic compounds based on azobenzene and azopyridine derivatives. The significance of the addition of ethanol as a stabilizer in chloroform-based solutions on the isomerization reaction of the hydroxy- and the 6-hydroxylalkoxy-substituted azo compounds was investigated. The results have revealed that the presence of a polar stabilizer in a solvent can significantly reduce the reaction rate constant of the dark cis-trans isomerization due to the formation of hydrogen bonds at both ends of the azo-chromophore, thereby inhibiting the isomerization. Furthermore, a stabilizer can facilitate the reversion of azo-hydrazone tautomers of azophenols to their azobenzene form, resulting in a decrease in the reaction rate constant. The research presented in this paper can be essential for scientists who study the kinetics of the trans-cis and the cis-trans isomerization reactions of azo-chromophores. The results show that the use of solvents with polar stabilizers should be rather avoided, as their usage without information about stabilizers can lead to different experimental data. The authors should ensure that detailed information about stabilizers used in unstable solvents is included in the experimental section of their works (a detail currently often omitted in the literature).

Spiropyrans exhibit reversible photochromism that strongly depends on solvent polarity; yet a quantitative understanding of this relationship remains incomplete. Here we combine detailed spectroscopic and kinetic experiments with ab initio calculations to investigate 5'-methoxy-1',3',3'-trimethyl-6-nitrospiro[chromene-2,2'-indoline] (SP). Ultraviolet irradiation at 368 nm populates the S3 (1ππ*) state, initiating the ring-opening reaction to the merocyanine (MC) form, which is subsequently followed by thermal ring-closing. Theoretical calculations indicate that photoexcited SP undergoes nonradiative relaxation to the S₁ charge-transfer state, from which the system reaches the ground state via a ring-opened conical intersection. Experimental kinetics studies have revealed that increasing solvent polarity slows relaxation and raises the activation energy from 89.7 kJ mol⁻1 in dioxane to 104.6 kJ mol⁻1 in acetone. Calculations have reproduced this trend, showing that polar solvents preferentially stabilize MC over the transition state. The observed blue shift of the MC absorption band with increasing polarity confirms the presence of negative solvatochromism. This combined experimental-theoretical analysis provides a quantitative framework linking solvent polarity, photochromic efficiency, and the activation energy in a model nitrospiropyran system.

This paper focuses on solvatochromic studies of a new synthesised BODIPY dye with piperonal and ortho-hydroxy aryl Schiff base substituents (BD-2-Schiff). The studied dye has been analysed by spectroscopic and computational techniques to have a deep insight into the impact of the solvents’ polarity and the specific interactions on the dye characteristics. The synthesized dye turns to be sensitive to external specific interactions, caused by protic solvents and acid, which change spectral characteristics of BODIPY-2-Schiff. The calculations by the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT) have been accomplished for the interpretation of the obtained experimental results. The synthesized dye has been evaluated as a photosensitizer for the light induced inactivation of Staphylococcus aureus (S. aureus) and Acinetobacter baumannii (A. baumannii). The synthesized BODIPY dye has shown a significant photocidal activity (above 90 %) against these pathogenic bacteria at low microgram concentrations and excitation with low doses of visible light (0.72 J/cm2; λ = 519 nm).

The family of Mn-based organic-inorganic hybrids has greatly expanded due to their advantages in applications. They also show superior bright and size-tunable photoluminescence and can be considered a perfect alternative to toxic lead-based compounds. In this work, we present the detailed structural, optical, and electrical characterization of ([(NH3CH2CH2)(3)NH])(2)[MnBr5]Br-5. The title compound exhibits a unique type of inorganic arrangement created by the trigonal bipyramids. It crystallizes in noncentrosymmetric space group R32, indicating its optical activity, piezoelectricity, and second-order optical nonlinearity proven by the second harmonic of light measurements. The studied crystals exhibit intense photoluminescence originating from the Mn(II) ion T-4(1)(G) -> (6)A(1) transition. The measured lifetime of the photoluminescence emission is <= 1.5 ms, while the measured quantum yield for both powder and crystal samples reaches similar to 70%.

The paper focuses on the synthesis of the chloro-, methyl and carbonyl derivatives of Benzodioxole-BODIPY dye (BODIPY- 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene). Three BODIPY dyes have been synthesized and characterized by biological, spectroscopic, crystallographic and computational methods. The influence of the electron donating and electron withdrawing properties of the substituents on the position of the absorption and emission bands have been analysed. The synthesized compounds have been evaluated as photosensitizers for the photodynamic inactivation of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The dyes revealed a significant photocidal activity against these pathogenic bacteria at low micromolar concentrations. The photo-toxic results showed that the synthesized dyes impact more affectively on S. aureus (Gram-positive bacteria) compared to Escherichia coli (Gram-negative bacteria).

The paper presents a series of azobenzene and azo pyridine compounds containing hydroxyl or 6-hydroxyhexyloxyl substituents. The nitrogen atom is located at the ortho-, meta- or para-position in the structure of azo pyridine derivatives. The impact of the structural features of azo chromophores on their thermal (DSC, TGA) and optical (UV-Vis) properties was investigated. The dark cis-trans isomerization kinetics was studied in ethanol and chloroform at 298 K. The formation of noncovalent hydrogen bonds between azo molecules and/or chromophore solvent was monitored using the 1H NMR spectroscopy and estimated by density functional theory (DFT) calculations. Based on experimental and computational studies we proposed the mechanism of the dark cis-trans isomerization for hydroxy-substituted azo compounds.

In this study we report the synthesis and photochromic properties of chiral azobenzene derivatives based on the 2-azabicycloalkane skeleton. The photochromic properties of newly synthesized family of azoben-zene derivatives have been studied using the UV/Vis spectroscopy. The interpretation of spectral features was supported by the results of the electronic-structure calculations. The experimental data confirm -typical for azobenzene -the occurrence of the trans-cis and the cis-trans photochemical reactions upon irradiation with the visible and UV light, respectively. On the other side, atypical thermal relaxation pro-cesses were observed, especially after UV light irradiation, which indicate that thermal back reaction can be not as straightforward as one could expect. The substituents located on the 2-azabicycloalkane lead to some changes in the electronic structure of studied compounds reflected in the changes of the band shapes in the electronic spectra.CO 2022 The Authors. Published by Elsevier B.V.

Crystallization of organic substances from solution in the presence of laser light is a relatively new concept. In this work we describe a unique way of increasing of local concentration of para-nitroaniline (pNA) in 1,4 -dioxane by using strongly absorbed laser light leading to controlled crystal growth.he key process enabling this control is laser induced thermocapillary Marangoni effect, which on microscopic scale results in near surface liquid flows. These flows are due to strong temperature gradients, formed locally by light absorption of the laser beam as well as induced changes of surface tension. As a result a strongly saturated in pNA sesille droplet is formed whose position can be can be effectively steered by beam manipulation. Such an approach enables not only para-nitroaniline crystal growth inside droplet itself but also control over supplying saturated solution portions to the area in which crystallization takes place.

Light-responsive self-assembly systems have emerged as a promising tool for controlling a multitude of molecular and macroscopic processes. A number of sophisticated applications of surfactants based on the azobenzene moiety have already been demonstrated including drug delivery and induction of functional changes in biologically active compounds. In most of these applications the switching time between the two compound states is substantial. However, a small number of systematic studies on the relationship between the chemical structure of the compound on the kinetics of photoisomerization and the influence of experimental conditions led us to undertake the studies described in this paper. Changes in the spectral characteristics resulting from reversible photoinduced trans-cis isomerization reaction of selected azobenzene-based surfactants, differing in the hydrophobic tail length, were determined in aqueous solutions employing UV–Vis absorption spectroscopy. The effect of the hydrophobic tail length, surfactant concentration, molecular environment and light intensity on the efficiency and kinetics of photoisomerization were investigated. Due to the thermal stability of both photochromic forms, it is possible to reversibly switch between two different photostationary states of the light-responsive surfactant in a controlled manner using light of two wavelengths (ultraviolet and blue). The results demonstrates that both the increasing concentration of azobenzene amphiphile and the increasing hydrophobic pendant tail length slow down the trans-cis photoisomerization, while the photochromic efficiency remains constant.

It is well known that light-induced multiple trans-cis-trans photoisomerizations of azobenzene derivatives attached to various matrices (polymeric, liquid crystalline polymers) result in polymer mass movement leading to generation of surface reliefs. The reliefs can be produced at small as well as at large light intensities. When linearly polarized light is used in the process, directional photo-induced molecular orientation of the azo molecules occurs, which leads to the generation of optical anisotropy in the system, providing that thermal effects are negligible. On the other hand, large reliefs are observed at relatively strong laser intensities when the optofluidization process is particularly effective. In this article, we describe the competitive thermocapillary Marangoni effect of polymer mass motion. We experimentally prove that the Marangoni effect occurs simultaneously with the optofluidization process. It destroys the orientation of the azopolymer molecules and results in cancelation of the photo-induced birefringence. Our experimental observations of polymer surface topography with atomic force microscopy are supported by suitable modelings.

Thermal cis-trans isomerization of azobenzene and azopyridine derivatives was studied. The impact of the structural features of azo derivatives on its isomerization kinetics being important for molecular switching materials was investigated experimentally and theoretically based on the density-functional theory (DFT). Eleven azo-dyes in which the phenyl rings were substituted in the para-position to NN– linkage were prepared. Additionally, their thermal properties were evaluated by thermogravimetric analysis and differential scanning calorimetry. DFT calculations were also used for optimization ground and transition state geometries, the density of states, electronic structures of studied azo-dyes. The kinetics of the dark-return cis to trans-form of azo-compounds was investigated after UV-irradiation. It was found that attaching hydroxyalkoxy-substituents to the azo-dyes structure retarding the photoisomerization process in comparison to the hydroxyl group. Moreover, dark-return cis to trans-isomer was ca. twice times faster for azopyridine derivatives than for their azobenzene analogues. The calculated rate constants were in qualitative agreement with the experimental values.

In light absorbing liquids optical trapping of solid micro-objects but also gas bubbles can be achieved and explained by the mechanisms involving the hydrodynamic whirls formation. The various forms of these whirls, that arise due to optothermal Marangoni effect induced by laser light beam, are able to accelerate the objects movement, transport them and subsequently trap at the laser beam center but also close to it. The usual light gradient field force and scattering force solely are insufficient and even not adequate to properly describe the mentioned by us particle trapping effects as the trap potential extends to much larger distances that the beam waist. We will demonstrate the mechanism of optical trapping and transporting of gas bubbles and will discuss the physics of whirls formation in this case. The numerical modelling of Marangoni flows at the liquid-gas interface confirms the experimental findings. We also demonstrate a novel type of trapping of micro-objects that occurs inside a toroidal whirl induced by laser in dye-doped oil. This type of trapping is quite unusual but allows to transport objects immobilized far from the beam waist just avoiding their excessive heating.

The subject of the research is a series of azo-dyes based on the quinoline structure, which are practically omitted as materials which use photoinduced optical anisotropy for applications. The work presents the kinetics of thermal cis-trans isomerization reaction of 5-azo-8-hydroxy-2-methylquinoline and 5,5'-((1E,1′E)-[1,1′-biphenyl]-4,4′-diylbis(diazene-2,1-diyl))bis(2-methylquinolin-8-ol) compounds. The impact of the structure of the substituent at the azo linkage on the cis-trans isomerization kinetics was investigated experimentally and theoretically using the UV–Vis spectroscopy and the density-functional theory (DFT). The kinetics of the dark-return of the cis-to trans-isomer of azoquinolines was investigated after UV-irradiation. It was found that attaching the nitro substituent to the azoquinolines structure retards the photoisomerization process in comparison to the other substituents (i.e. F, Cl, Br, N atoms or CH3, OH, COOH, OCH3 groups). The calculated rate constants were in qualitative agreement with the experimental values. To the best of our knowledge, the cis-trans isomerization kinetics for azoquinolines has not been studied yet.

To the best of our knowledge, for the first time the effect of the presence of pyridine vs benzene structure in azochromophore on thermally driven cis-trans isomerization in a solid state is presented. The influence of the molar mass of the polymer matrix, in which the chromophores were molecularly dispersed, was revealed. The poly(etherimide) with a weight-average molecular weight within the range of 2 600-33 300 g/mol was applied as a matrix. The fragility parameter of the matrices was discussed also in the context of observed relationship between cis-trans isomerization in various matrixes. Additionally, thermal back reaction from the cis to the trans-form of 4-[4-(6-hydroxyhexyloxy)phenylazo]pyridine and 4-[4-(6-hydroxyhexyloxy)phenylazo]benzene in DMF solution was investigated. The holographic grating recording was realized in the poly(etherimide) containing azopyridine of different content.

A new family of organic-inorganic hybrid layered materials based on cadmium and zinc sulfates was synthesized using 1,2-phenylenediamine (OPD), 1,3-phenylenediamine (MPD), and 1,4-phenylenediamine (PPD) as organic templates and ligands. The diamines act as structure-directing agents to obtain one-dimensional (1D), 2D, and 3D frameworks. Six new materials were obtained utilizing a simple, solvent-free synthesis approach: 1D: (OPD)(2)ZnSO4 1, (OPD)(2) CdSO4 2; 2D: (MPD)(2) ZnSO(4 )3, (MPD)(2) CdSO4 4; 3D: (PPD)ZnSO4 5, (PPD)CdSO4 6. The synthesis method proved to be scalable and robust. The crystal structures were determined using data from X-ray powder diffraction measurements (XRPD). It was observed that the type of amine determines the dimensionality of the obtained materials. 1D, 2D, and 3D structures were obtained using ortho-, meta-, and para-phenylenediamine isomers, respectively. The phase purity of the samples was confirmed by elemental analysis, and the morphology of the crystallites was studied using scanning electron microscopy. The thermal stability was determined by thermogravimetry and nonambient XRPD techniques. Additional characterization was performed for the two non-centrosymmetric, polar materials 3 and 4. Second-order nonlinear optical properties were examined using both experimental measurements (second harmonic generation) and theoretical calculations.

Single-component azobenzene-based phototropic liquid crystals (PtLC) are promising materials that have started to be explored for photonic applications. One of the essential factors determining the applicability of these materials is the rate of the thermally driven cis-trans isomerization. In this paper, the kinetics of the thermal back cis-to-trans reaction in a pure 4-hexyl-4'-methoxyazobenzene (6-AB-O1) compound in its isotropic liquid and nematic phases is studied (the undoped LC). The reaction rate constants, activation energies and thermal activation parameters were determined based on spectroscopic studies. The reaction kinetics is compared to that measured for the compound dissolved in chloroform. The results demonstrate that the thermal back reaction depends on the phase and molecular environment of the cis-isomer. Moreover, the effect of temperature on the absorption spectra of 6-AB-O1 in its isotropic, nematic and crystalline phases is examined. The changes in the compound's absorption spectra in the respective phases have been correlated to the positional order parameter S.

A member of the propellane family – a novel chiral compound DDDDP – that shows second harmonic generation in its crystalline form.