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Among various classes of Photoluminescent (PL) compounds, soft-matter based materials in which chromophores are embedded in a Liquid-Crystal (LC) host polymer prove to be very attractive in the production of flexible panels and on-off temperature switches. Actually, the obtainment of low cost, easily synthesizable, and stable organic molecules soluble in the LC matrix is a challenge for both scholars and technologists. Here we describe the synthesis of two new emissive dyes based on a dicyanophenylenevinylene and on a bis-azobenzene core whose PL properties were investigated as neat solids, in solution, and in particular in a dye-doped LC nematic polymer often employed in PDLC applications. 1H NMR and 13C NMR spectroscopy allow the characterization of all compounds Their thermotropic liquid- crystalline (LC) properties were examined by differential scanning calorimetry and polarizing optical microscopy. Photoluminescence properties were characterized by fluorescence spectra.

Herein we designed three novel fluorescent brightening agents based on a benzodifuran skeleton. The compounds are colorless fluorophores emitting in the blue region with an improved water solubility and ability to interact with living cells. A complete understanding of the emission mechanisms was achieved by Density Functional Theory study based on X-ray crystallographic analysis. The fluorescence quantum yields were measured in different solvents and at different pH values. The ability of the different fluorophores to stain cell compartments of plant root samples was tested in water- and glycerol-based solutions. Through fluorescence microscopy technique two probes with a different functionalized branching chain proved to be efficient stains for plant root cell wall. The cationic probe has no harmful effect on plant tissues and is suitable for in vivo fluorescent visualization of plant root cell boundaries. This study sheds light on the potential use of brighteners containing a central benzodifuran core as tools for imaging of fixed and alive plant tissues.

Two new complexes were obtained by reaction of zinc (II) acetate with 4-fluoro-N'-(pyridin-2-ylmethylene) benzohydrazide or with 4-(hexyloxy)-N'-(pyridin-2-ylmethylene)benzohydrazide ligands in pyridine. Both ligands have a pyridinyl-hydrazone moiety able to act as a mono-negative tridentate ligand toward zinc ion in 2:1 stoichiometric ratio, producing an octahedral environment. The derived complexes are poor emitters in diluted solution. Instead, they exhibit intense blue fluorescence in the solid state due to AIE (aggregation induced emission) effect. The crystalline complexes are bright yellow in natural light and blue under UV–visible light with remarkable Stokes Shifts. Their photoluminescence quantum yields are ranging 20–30%, making them very promising as fluorophore dopants for blue emissive layers. One ligand and its complex were characterized by single crystal X-ray diffraction analysis that revealed an almost planar conformation of two ligands coordinated to the metal and the presence of significant π-π stacking of molecules at about 3.4 A.

In the field of optical sensors, small molecules responsive to metal cations are of current interest. Probes displaying aggregation-induced emission (AIE) can solve the problems due to the aggregation-caused quenching (ACQ) molecules, scarcely emissive as aggregates in aqueous media and in tissues. The addition of a metal cation to an AIE ligand dissolved in solution can cause a “turn-on” of the fluorescence emission. Half-cruciform-shaped molecules can be a winning strategy to build specific AIE probes. Herein, we report the synthesis and characterization of a novel L-shaped fluorophore containing a benzofuran core condensed with 3-hydroxy-2-naphthaldehyde crossed with a nitrobenzene moiety. The novel AIE probe produces a fast colorimetric and fluorescence response toward zinc (II) in both in neutral and basic conditions. Acting as a tridentate ligand, it produces a complex with enhanced and red-shifted emission in the DR/NIR spectral range. The AIE nature of both compounds was examined on the basis of X-ray crystallography and DFT analysis.

Zinc (II) cation is an environmentally friendly metal, less expensive, easy to dispose of, and managed. Highly engineered symmetric systems can be built using zinc (II) atoms as the metal nodes of hybrid organic-inorganic supramolecular structures. In biological contexts, luminescent zinc-based nanoprobes are in growing demand. Specifically, they are currently employed to detect biologically and environmentally relevant analytes, in therapeutic drug delivery, and for bioimaging and diagnostic techniques monitoring aspects of cellular functions. This review will provide a systematic and consequential approach to zinc-based nanoprobes, including zinc-based MOFs and other zinc-based organized nanoparticles. A progression from detecting the biological target to the intracellular sensing/marking/carriage has been followed. A selection of significant cutting-edge articles collected in the last five years has been discussed, based on the structural pattern and sensing performance, with special notice to living cell bioimaging as the most targeted and desirable application.

Aggregation-induced emission (AIE) compounds display a photophysical phenomenon in which the aggregate state exhibits stronger emission than the isolated units. The common term of “AIEgens” was coined to describe compounds undergoing the AIE effect. Due to the recent interest in AIEgens, the search for novel hybrid organic–inorganic compounds with unique luminescence properties in the aggregate phase is a relevant goal. In this perspective, the abundant, inexpensive, and nontoxic d10 zinc cation offers unique opportunities for building AIE active fluorophores, sensing probes, and bioimaging tools. Considering the novelty of the topic, relevant examples collected in the last 5 years (2016–2021) through scientific production can be considered fully representative of the state-of-the-art. Starting from the simple phenomenological approach and considering different typological and chemical units and structures, we focused on zinc-based AIEgens offering synthetic novelty, research completeness, and relevant applications. A special section was devoted to Zn(II)-based AIEgens for living cell imaging as the novel technological frontier in biology and medicine.

The development of new organic simple and low-cost fluorophores is a current topic. To date innovative solutions include azo dyes because of the unique absorption behavior, but the azo group gives poor luminophores in the solid state. In order to produce a luminescent azo dye, we synthesized compound A2, 4,4′-((1,1′)-(2,5-dimethoxy-1,4-phenylene)bis(diazene-2,1-diyl))dianiline, and its symmetrical Schiff-base derivative C2. The new compound C2 is a weakly luminescent fluorophore in the crystalline phase and when employed as building blocks in self-assembly of zinc (II) coordination polymer. Nevertheless, if used as a dopant in PS and PVK, C2 shows enhanced fluorescence and represents a good on-off naked-eye switch when dispersed in a room-temperature nematic polymer.

From a diamino dicyano-phenylenevinylene skeleton a symmetrically di-salen dye was obtained and employed both as a dopant in non-emissive polymer matrixes and as building blocks in the preparation of a zinc self-assembly polymer. The new fluorophore C1 belongs to the class of the luminescent liquid crystals (LLCs). The molecule produces red emission in the crystalline phase and yellow luminescence in the nematic phase, which dramatically decreases in on-off switch mode after LC order was lost. Both C1 and its self-assembly zinc-based coordination polymer suffers a lot aggregation caused quench effect (ACQ). Conversely, thin films obtained by dispersion in polystyrene (PS) and poly(9-vinylcarbazole) (PVK) show remarkably enhanced fluorescence, reaching the noteworthy value of 77% Photoluminescence Quantum Yield (PLQY) for the PVK doped sample.

FSG acknowledges the CINECA award under the ISCRA initiative (HP10BJO47B) for the availability of high-performance computing resources and support., The phase transitions between paraelectric (PE) and ferroelectric (FE) isomorph phases of LiNbO3 have been investigated quantum mechanically by using a Gaussian-type basis set, the B3LYP hybrid functional and the CRYSTAL17 code. The structural, electronic and vibrational properties of the two phases are analyzed. The vibrational frequencies evaluated at the Γ point indicate that the paraelectric phase is unstable, with a complex saddle point with four negative eigenvalues. The energy scan of the A2u mode at −215 cm−1 (i215) shows a dumbbell potential with two symmetric minima. The isotopic substitution, performed on the Li and Nb atoms, allows interpretation of the nontrivial mechanism of the phase transition. The ferroelectric phase is more stable than the paraelectric one by 0.32 eV. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.--//-- Published under CC BY 4.0 licence., CINECA HP10BJO47B; Institute of Solid State Physics, University of Latvia as the Center of Excellence is supported through the Framework Program for European universities Union Horizon 2020, H2020-WIDESPREAD-01–2016–2017-TeamingPhase2 under Grant Agreement No. 739508, CAMART2 project.

In this work, a membrane probe (NR18) with a Nile Red-based chromophore, a long tail of 18 carbon atoms and a zwitterionic head was synthesized. The probe is optimized to remain anchored to the phospholipid bilayer without internalizing. NR18 was fully characterized chemically and optically and showed marked solvatochromism. Incorporation into model membranes of LUVs and GUVs having different compositions, demonstrated that the probe could be used to discriminate the lipid order in membranes, based on the fluorescent radiation emitted. Spectrophotometric and fluorimetric measurements on LUVs showed that the emission wavelength increases with temperature, confirming the increase in fluidity and hydration in membranes at higher temperatures. DFT simulations helped us to clarify the impact of NR18 on the membrane thickness and the order parameter showing that NR18 does not cause substantial perturbation in the bilayer. Moreover, we demonstrated that the presence of an enaminic terminal group is mainly responsible for the ability of NR18 to have a different fluorescence in Ld and Lo membranes.

Solid-state emitters exhibiting mechano-fluorochromic or thermo-fluorochromic responses represent the foundation of smart tools for novel technological applications. Among fluorochromic (FC) materials, solid-state emissive coordination complexes offer a variety of fluorescence responses related to the dynamic of noncovalent metal-ligand coordination bonds. Relevant FC behaviour can result from the targeted choice of metal cation and ligands. Herein, we report the synthesis and characterization of two different colour emitters consisting of zinc complexes obtained from N,O bidentate ligands with different electron-withdrawing substituents. The two complexes are blue and orange solid-state fluorophores, respectively, highly responsive to thermal and mechanical stress. These emitters show a very different photoluminescent (PL) pattern as recorded before and after the annealing treatment. Through X-ray structural analysis combined with thermal analysis, infrared (IR) spectroscopy, PL, and DFT simulation we provide a comprehensive analysis of the structural feature involved in the fluorochromic response. Notably, we were able to correlate the on-off thermo-fluorochromism of the complexes with the structural rearrangement at the zinc coordination core.

Tridentate ligands are simple low-cost pincers, easy to synthetize, and able to guarantee stability to the derived complexes. On the other hand, due to its unique mix of structural and optical properties, zinc(II) ion is an excellent candidate to modulate the emission pattern as desired. The present work is an overview of selected articles about zinc(II) complexes showing a tuned fluorescence response with respect to their tridentate ligands. A classification of the tridentate pincers was carried out according to the binding donor atom groups, specifically nitrogen, oxygen, and sulfur donor atoms, and depending on the structure obtained upon coordination. Fluorescence properties of the ligands and the related complexes were compared and discussed both in solution and in the solid state, keeping an eye on possible applications.

We developed a new benzodifuran derivative as the condensation product between 2,6-diamino-4-(4-nitrophenyl)benzo[1,2-b:4,5-b&rsquo, ]difuran-3,7-dicarboxylate and 3-hydroxy-2-naphthaldehyde. The intramolecular hydrogen-bond interactions in the terminal half-salen moieties produce a sterically encumbered highly conjugated main plane and a D-A-D (donor-acceptor-donor) T-shaped structure. The novel AIEgen (aggregation-induced enhanced emission generator) fulfils the requirement of RIR (restriction of intramolecular rotation) molecules. DR/NIR (deep red/near infrared) emission was recorded in solution and in the solid state, with a noteworthy photoluminescence quantum yield recorded on the neat crystals which undergo some mechanochromism. The crystal structure study of the probe from data collected at a synchrotron X-ray source shows a main aromatic plane &pi, stacked in a columnar arrangement.

Two novel symmetrical bis-azobenzene red dyes ending with electron-withdrawing or donor groups were synthesized. Both chromophores display good solubility, excellent chemical, and thermal stability. The two dyes are fluorescent in solution and in the solid-state. The spectroscopic properties of the neat crystalline solids were compared with those of doped blends of different amorphous matrixes. Blends of non-conductive and of emissive and conductive host polymers were formed to evaluate the potential of the azo dyes as pigments and as fluorophores. Both in absorbance and emission, the doped thin layers have CIE coordinates in the spectral region from yellow to red. The fluorescence quantum yield measured for the brightest emissive blend reaches 57%, a remarkable performance for a steadily fluorescent azo dye. A DFT approach was employed to examine the frontier orbitals of the two dyes.

Two novel polyimines were synthesized from a benzodifuran based diamino monomer and two dialdehydes bearing bulky groups and a flexible spacer. The polymers display tuned luminescence performance according to the presence of half-salen groups. The effect of the intramolecular bond on the emission properties were examined. Two model compounds, replicating the same emissive Schiff base cores, were synthetized. From the models, dye-doped blends in the fluorophore/matrix ratio, resembling the polymers, were produced. Amorphous thin films of the covalent polymers and the polymeric blends were obtained by spin-coating technique. The Photoluminescent (PL) response of the different macromolecular systems were qualitatively and quantitatively examined and compared.

A new 5-(4-((2-(benzothiazole-2-carbonyl)hydrazono)methyl)-3-hydroxyphenoxy)-N,N,N-trimethylpentan-1-aminium bromide (BTABr) fluorescent and colorimetric pH probe was easily synthesized by the condensation reaction of benzothiazole-2-carbohydrazide with 5-(4-formyl-3-hydroxyphenoxy)-N,N,N-trimethylpentan-1-aminium bromide. The benzothiazole moiety provided the emissive part of the molecule and the charged trimethyl amino group guaranteed outstanding solubility in water, for an organic molecule. pH titration experiments indicated that the probe is useful for monitoring acidic and alkaline solutions, turning reversibly in color/fluorescence just at a neutral pH value. Naked-eye colorimetric response was observed both in solution and in the solid state. In addition, the probe showed high stability and selectivity and large Stokes shifts. Because of these features, BTABr can potentially work as an on-off real-time pH sensor for intracellular pH imaging. The crystal structure of BTABr examined by single-crystal analysis showed a planar geometry of the molecule and confirmed the presence of a molecular stacking between molecules joined in a complex tridimensional hydrogen bonding pattern.

Three zinc (II) complexes were synthesized from O,N,O-tridentate ligands with a charged side chain and a different electron withdrawing substituent. Metallated polymers with emission color tuning based on the same ligands moved interest. In the present study we collected information on the coordination environment and on the photoluminescence performance of the related model complexes. In pyridine solution RGB (red-greenblue) emission was achieved by lowering the withdrawing strength of the substituent. Two of the ligands were characterized by single crystal X-ray diffraction analysis that revealed the keto form and the shape adopted as uncoordinated molecules.

Most linear peptides directly interact with membranes, but the mechanisms of interaction are far from being completely understood. Here, we present an investigation of the membrane interactions of a designed peptide containing a non-natural, synthetic amino acid. We selected a nonapeptide that is reported to interact with phospholipid membranes, ALYLAIRKR, abbreviated as ALY. We designed a modified peptide (azoALY) by substituting the tyrosine residue of ALY with an antimicrobial azobenzene-bearing amino acid. Both of the peptides were examined for their ability to interact with model membranes, assessing the penetration of phospholipid monolayers, and leakage across the bilayer of large unilamellar vesicles (LUVs) and giant unilamellar vesicles (GUVs). The latter was performed in a microfluidic device in order to study the kinetics of leakage of entrapped calcein from the vesicles at the single vesicle level. Both types of vesicles were prepared from a 9:1 (mol/mol) mixture of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and POPG (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho(1′-rac-glycerol). Calcein leakage from the vesicles was more pronounced at a low concentration in the case of azoALY than for ALY. Increased vesicle membrane disturbance in the presence of azoALY was also evident from an enzymatic assay with LUVs and entrapped horseradish peroxidase. Molecular dynamics simulations of ALY and azoALY in an anionic POPC/POPG model bilayer showed that ALY peptide only interacts with the lipid head groups. In contrast, azoALY penetrates the hydrophobic core of the bilayers causing a stronger membrane perturbation as compared to ALY, in qualitative agreement with the experimental results from the leakage assays., Membranes, 10 (10)

The study of the cell membrane is an ambitious and arduous objective since its physical state is regulated by a series of processes that guarantee its regular functionality. Among the different methods of analysis, fluorescence spectroscopy is a technique of election, non-invasive, and easy to use. Besides, molecular dynamics analysis (MD) on model membranes provides useful information on the possibility of using a new probe, following its positioning in the membrane, and evaluating the possible perturbation of the double layer. In this work, we report the rational design and the synthesis of a new fluorescent solvatochromic probe and its characterization in model membranes. The probe consists of a fluorescent aromatic nucleus of a 3-hydroxyflavone moiety, provided with a saturated chain of 18 carbon atoms and a zwitterionic head so to facilitate the anchoring to the polar heads of the lipid bilayer and avoid the complete internalization. It was possible to study the behavior of the probe in GUV model membranes by MD analysis and fluorescence microscopy, demonstrating that the new probe can efficiently be incorporated in the lipid bilayer, and give a color response, thanks to is solvatochromic properties. Moreover, MD simulation of the probe in the membrane supports the hypothesis of a reduced perturbation of the membrane physical state.

Two oligomers with different molecular weight were produced. Fluorescence properties were examined both in solutions and in the solid state. In the solid state, molecular weight turned out to be an important factor influencing the aggregation structures and therefore the emission of the compounds, in colour and intensity. The neat compounds emit two different colours, blue and yellow, with increasing the molecular weight, whereas both compounds are blue emitters in solution and dispersed in host polymers. Dissolved in a LC host polymer and in a PVK matrix, they displayed noteworthy photoluminescence quantum yields.

Three multifunctional ligands containing 2,5-disubstituted-oxadiazole units including an ortho/meta/para-substituted pyridine moiety have been synthesized. The reactions of the ligands with zinc(II) acetate in pyridine gave crystalline complexes with the general formula [Zn(Li)2py2]. On the other hand, zinc-assisted self-assembly of the ligands in the absence of pyridine led to stable glassy networks with the general stoichiometry [Zn(Li)2]. The direct involvement of the pyridine moiety in the coordination of the metal was observed in all cases. The spectroscopic behaviour of the complexes was explored and compared. In particular, medium-to-high photoluminescent quantum yields were observed for thin films produced from both crystalline and glass samples. Molecular and periodic calculations were performed by using DFT to rationalize the photophysical behaviour.

A tripodal colorimetric chemosensor named PoPAP was used as a fluorescence probe towards the first-row transition cations. A real-time fluorescence enhancement in presence of zinc (II) and chromium (III) cations was detected in slightly acidic water solution. The same cations partially quenched the emission of the ligand in basic medium. As function of pH conditions, different coordination modes of the chemosensor in complex with zinc (II) were isolated and analyzed. Fluorescence color difference of PoPAP in complex with zinc allows for an easy detection by naked-eye at acidic and basic conditions. The solid forms of PoPAP in complex with zinc show a reduction to about one third of the fluorescence quantum yield as compared with the value in its unbound form and due to ACQ phenomena. DFT calculations, starting from single crystal structure analysis are in good agreement with the experimental emission patterns. Two different mechanisms of electron density transfer from ground to excited state were analyzed as function of pH conditions.

From a dicyano-phenylenevinylene (PV) and an azobenzene (AB) skeleton, two new symmetrical salen dyes were obtained. Terminal bulky substituents able to reduce intermolecular interactions and flexible tails to guarantee solubility were added to the fluorogenic cores. Photochemical performances were investigated on the small molecules in solution, as neat crystals and as dopants in polymeric matrixes. High fluorescence quantum yield in the orange-red region was observed for the brightest emissive films (88% yield). The spectra of absorption and fluorescence were predicted by Density Functional Theory (DFT) calculations. The predicted energy levels of the frontier orbitals are in good agreement with voltammetry and molecular spectroscopy measures. Employing the two dyes as dopants of a nematic polymer led to remarkable orange or yellow luminescence, which dramatically decreases in on-off switch mode after liquid crystal (LC) order was lost. The fluorogenic cores were also embedded in organic polymers and self-assembly zinc coordination networks to transfer the emission properties to a macro-system. The final polymers emit from red to yellow both in solution and in the solid state and their photoluminescence (PL) performance are, in some cases, enhanced when compared to the fluorogenic cores.

A new complex was obtained starting from a pyridyl/phenolic/benzothiazole functionalized ligand (BPAP) with zinc acetate. The structural and photoluminescence properties of the complex were investigated by X-ray diffraction and confirmed by DFT calculations. By comparing the results with previous studies, we found that the mode of binding of the sensor was influenced by the pH of the medium, changing the zinc coordination sphere. In a basic aqueous solution, the metal coordinates two neutral nitrogen atoms and two negative sites, the phenate oxygen and the deprotonate amide nitrogen and a water molecule. In this condition, the ligand was found to behave as a more sensitive naked eye fluorescence chemosensor towards Zn2+, showing blue photoluminescence with a lower detection limit of 375 nM.