Synthesis and Structural Analysis of Push-Pull Imidazole-Triazole Based Fluorescent Bifunctional Chemosensor for CU2+ and FE2+ Detection

[Abstract] Fluorescent imidazole-triazole based ligands L1 and L2 have been designed as chemical push-pull chemosensors for divalent metal ions and synthesized through palladium-catalyzed cross-coupling reactions using indium organometallics and click chemistry. The novel ligands exhibit intense absorption in the ultraviolet region with high molar extinction coefficients, and strong fluorescence emission with large Stokes displacements. On the basis of UV–Vis absorption spectroscopy and fluorescence emission data in acetonitrile, L1 is shown as a bifuncional chemosensor with differential response for Fe2+ and Cu2+ over a range of selected 3d divalent and other metal ions. The binding site of the ligand was established by single-crystal X-ray diffraction and 1H NMR spectroscopy studies. The association constants, determined by spectrofluorimetric titrations, show a steady binding affinity of L1 for Cu2+ and Fe2+ in comparison with other previously reported fluorescent bidentate chemosensors, offering the lowest limit of detection (LOD) with Cu2+. DFT calculations provide a rationale properly understanding and interpreting the experimentally observed results. Indeed, a mechanism of the different optical responses of L1 towards 3d divalent metal ions is proposed.We thank the Spanish Ministerio de Ciencia, Innovación y Universidades (PGC2018-097792-B-I00), Xunta de Galicia (GRC2018/039 and ED431B 2020/52) and EDRF funds for financial and human support. ADL thanks the Xunta de Galicia for a predoctoral fellowship (EDA 481A-2020/017). LV thanks CACTI for X-ray measurementsXunta de Galicia; GRC2018/039Xunta de Galicia; ED431B 2020/52Xunta de Galicia; ED 481A-2020/01

Turn on fluorescence sensing of Zn2+ based on fused isoindole-imidazole scaffold

Optical chemosensors caused a revolution in the field of sensing due to their high specificity, sensitivity, and fast detection features. Imidazole derivatives have offered promising features in the literature as they bear suitable donor/acceptor groups for the selective analytes in the skeleton. In this work, an isoindole-imidazole containing a Schiff base chemosensor (1-{3-[(2-Diethylamino-ethylimino)-methyl]-2-hydroxy-5-methyl-phenyl}-2H-imidazo[5,1-a]isoindole-3,5-dione) was de-signed and synthesized. The complete sensing phenomena have been investigated by means of UV-Vis, fluorescence, lifetime measurement, FT-IR, NMR and ESI-MS spectroscopic techniques. The optical properties of the synthesized ligand were investigated in 3:7 HEPES buffer:DMSO medium and found to be highly selective and sensitive toward Zn2+ ion through a fluorescence turn-on response with detection limit of 0.073 µm. Furthermore, this response is effective in gel form also. The competition studies reveal that the response of the probe for Zn2+ ion is unaffected by other relevant metal ions. The stoichiometric binding study was performed utilizing Job’s method which indicated a 1:1 sensor–Zn2+ ensemble. Computational calculations were performed to pinpoint the mechanism of sensin

A Turn-On Fluorescent Chemosensor for Cyanide Ion Detection in Real Water Samples

We have designed and synthesized a novel simple colorimetric fluorescent probe with aggregation-induced emission (AIE) properties. Probe 5-(4-(diphenylamine)phenyl) thiophen-2-formaldehyde W exhibited a turn-on fluorescent response to cyanide ion (CN−), which induces distinct visual color changes. Probe W exhibited a highly selective and sensitive ratiometric fluorescence response for the detection of CN− over a wide pH range (4–11) and in the presence of common interferents. The linear detection of CN− over the concentration range of 4.00–38.00 µM (R2 = 0.9916, RSD = 0.02) was monitored by UV-Vis absorption spectrometry (UV-Vis) with the limit of detection determined to be 0.48 µM. The linear detection of CN− over the concentration range of 8.00–38.00 µM was examined by fluorescence spectrophotometry (R2 = 0.99086, RSD = 0.031), and the detection limit was found to be 68.00 nM. The sensing mechanisms were confirmed by 1H NMR spectroscopic titrations, X-ray crystallographic analysis, and HRMS. Importantly, probe W was found to show rapid response, high selectivity, and sensitivity for cyanide anions in real water samples, over the range of 100.17∼100.86% in artificial lake water and 100.54∼101.64% in running water by UV-Vis absorption spectrometry, and over the range of 99.42∼100.71% in artificial lake water and 100.59∼101.17% in running water by fluorescence spectrophotometry. Importantly, this work provides a simple and effective approach which uses an economically cheap and uncomplicated synthetic route for the selective, sensitive, and quantitative detection of CN− ions in systems relevant to the environment and health

Luminescence and Palladium: the Odd couple

The synthesis, photophysical properties, and applications of highly fluorescent and phosphorescent palladium complexes are reviewed, covering the period 2018–2022. Despite the fact that the Pd atom appears closely related with an efficient quenching of the fluorescence of different molecules, different synthetic strategies have been recently optimized to achieve the preservation and even the amplification of the luminescent properties of several fluorophores after Pd incorporation. Beyond classical methodologies such as orthopalladation or the use of highly emissive ligands as porphyrins and related systems (for instance, biladiene), new concepts such as AIE (Aggregation Induced Emission) in metallacages or in coordination-driven supramolecular compounds (CDS) by restriction of intramolecular motions (RIM), or complexes showing TADF (Thermally Activated Delayed Fluorescence), are here described and analysed. Without pretending to be comprehensive, selected examples of applications in areas such as the fabrication of lighting devices, biological markers, photodynamic therapy, or oxygen sensing are also here reported

π-conjugated pyrenoimidazole derivatives: synthesis, spectroscopic and crystallographic studies

This PhD thesis was aimed at the design and synthesis of new functional phenyl-pyrenoimidazole derivatives and the development of these compounds as novel chromophores/uorophores and supramolecular synthons for organic crystal engineering. An efficient and modular one-pot condensation reaction between 4,5-pyrenedione and various benzaldehydes in presence of ammonium acetate and acetic acid was used to prepare all the new phenyl-pyrenoimidazoles investigated in this thesis work. There are three major projects accomplished in this thesis. The first project investigated the properties of two new benzaldehyde-substituted pyrenoimidazoles, in which the electron-withdrawing formyl group is attached to the para and meta position of the phenyl group. These two isomers were characterized by various spectroscopic, X-ray single crystallographic analyses, in conjunction with density functional theory (DFT) calculations. The interactions of these two new compound with uoride anions through hydrogen bonds were examined as well, and the results demonstrated the applicability of the para-benzaldehyde substituted pyrenoimidazole as an efficient ratiometric uorescence probe for uoride anion. In the second project, a series of phenyl-pyrenoimidazole substituted with various organic functional groups (including CH₃, Cl, Br, OCH₃, CHO, and NO₂) were synthesized and their structure photophysical property relationships were subsequently studied by UV-Vis absorption and uorescence spectroscopy. Xray crystallographic and molecular electrostatic potential (MEP) analyses were undertaken to disclose the interplay of various non-covalent forces that govern the crystal packing of these pyrenoimidazole molecules. The results indicated that the substituent group is an important factor controlling the crystal structural properties, which attests to the possibility of using various phenylpyrenoimidazole derivatives as tunable supramolecular synthons for crystal engineering. In the third project, hydroxyl and alkoxyl-substituted phenyl-pyrenoimidazole derivatives were prepared and investigated for comparative studies of the effects of hydrogen bonding and π - π interactions on their crystallization behaviors. To construct different organic crystals, various aromatic carboxylic acids were used with these pyrenoimidazoles. The resulting crystal structures were analyzed by X-ray crystallography to show the formation of different supramolecular network structures in the solid state. Based on the crystallographic data obtained, Hirshfeld surface analysis and quantum theory of atoms in molecules (QTAIM) calculations were carried out to quantitatively interpret and comprehensively visualize the various intermolecular forces, such as hydrogen bonding, π - π, C-H...π, and H...H interactions, in the pyrenoimidazole crystals and co-crystals

Advances in optical sensors for persistent organic pollutant environmental monitoring

Optical chemical sensors are widely applied in many fields of modern analytical practice, due to their simplicity in preparation and signal acquisition, low costs, and fast response time. Moreover, the construction of most modern optical sensors requires neither wire connections with the detector nor sophisticated and energy-consuming hardware, enabling wireless sensor development for a fast, in-field and online analysis. In this review, the last five years of progress (from 2017 to 2021) in the field of optical chemical sensors development for persistent organic pollutants (POPs) is provided. The operating mechanisms, the transduction principles and the types of sensing materials employed in single selective optical sensors and in multisensory systems are reviewed. The selected examples of optical sensors applications are reported to demonstrate the benefits and drawbacks of optical chemical sensor use for POPs assessment

Studies of polycyclic aromatic hydrocarbon-based organic materials for optoelectronic applications

π-Conjugated polycyclic aromatic hydrocarbons (PAHs) have found increasing applications in the fields of organic photonics and optoelectronics owing to their highly tunable photophysical properties, redox activity, and supramolecular self-assembling behavior. This PhD thesis mainly focuses on the studies of four classes of PAH-based organic materials, namely diphenyl dibenzofulvenes (DP-DBFs), pentacenetetraone-derived π-extended tetrathiafulvalene analogues (TTFAQ-AQ),donor/acceptor(D/A)-functionalized phenanthroimidazoles(PIs), and bis(diarylmethylene)dihydroanthracenes (Ar₄-DHAs). DP-DBFs have been known to show intriguing crystallization-induced emission enhancement(CIEE) and aggregation-induced emission (AIE) properties; however, the molecular origins for them to exhibit such unique photophysical properties have not yet been clearly reported in the literature. In the first project of this thesis work, we designed and prepared a series of DP-DBFs with various substituents. With the aid of solution and solid-state fluorescence spectroscopic analysis, the AIE and CIEE properties of DP-DBFs we reinvestigated. Our studies confirmed that the twist angle around the C=C bond in the DP-DBF is a key factor to control its fluorescence behavior. In the second study, the structure-property relationship of TTFAQ-AQs were systematically examined. Analyses of their redox properties and electronic band gaps suggested that they could be promising organic semiconducting materials. Moreover, the synthesized TTFAQ-AQs featured double curved π-surfaces that contain both electron-deficient and electron-rich segments. In this way, they can serve as versatile supramolecular partners to interact with 3-dimensional π-conjugated host molecules such as fullerenes. A benzo-fused TTFAQ-AQ derivative was observed to form organized organic co-crystals with electron deficient C₇₀ fullerene through concave- convex shape complementarity and strong donor-acceptor interactions. The results point to promising application in redox-active organic electronic materials. The third project embarked on the design of novel PI-derived organic chromophores and fluorophores. PI derivatives containing electron-donating dithiafulvenyl (DTF) groups and electron-accepting aldehyde groups were synthesized and characterized in terms of their fluorescence and electrochemical properties. The DTF-functionalized PI derivatives were found to show fluorescence sensitivity to singlet oxygen through a chemiluminescent mechanism. Moreover, the chemical oxidative dimerization of DTF end groups led to the construction of a new type of TTFV-PI macrocycles, which showed interesting fluorescence turn-on/off behavior when they interacted with C₆₀ and C₇₀ fullerenes at different ratios. These features make the synthesized PI materials interesting candidates in the fabrication of efficient fluorescence sensors for singlet oxygen and fullerenes. The last project focuses on the synthesis, characterization, and mechanistic analyses on the photocyclization of a series of Ar₄-DHAs. We have made three different derivatives functionalized with methoxy groups at various positions of the phenyl ring, a tethered Ar₄-DHA derivative as a rigid model compound, and their photocyclized products. Although the cyclodehydrogenation reaction of this class of PAHs through the Scholl reaction has been well studied, photocyclization reaction still lacks sufficient understanding and evidence to support detailed mechanisms. In our work, it has been observed that the photocyclization only happens on one side of Ar₄-DHA through a two-fold Mallory reaction. To better understand the mechanisms involved and the molecular reasons behind the two-fold Mallory reaction, we have utilized experimental and theoretical approaches including X-ray crystallographic analyses and density functional theory (DFT) calculations. The frontier molecular orbital (FMO) analyses offered convincing explanation for the regioselectivity of the two-fold Mallory reaction on a Ar₄-DHA. In addition, the importance of the position of the methoxy substituent on the mechanism of photocyclization has been revealed; in particular, when the methoxy groups are at the ortho positions, cyclodemethoxylation occurred instead of cyclodehydrogenation. Collectively, the work in Chapter 5 offers in-depth understanding of the photochemical properties of Ar₄-DHAs as well as valuable guidance for future work on the synthesis of π-extended PAHs and nanographenes from readilly accessbile Ar₄-DHA precursors

Synthesis, Modification and Biological Activity of Hexacoordinate Silicon(IV) Complexes

The metalloid silicon is one of the most versatile elements of the world. Besides its widespread occurrence in the lithosphere, silicon containing compounds, for example the polymeric silicones, are used in numerous applications of the modern world. Moreover, the digital revolution and the progress in the photovoltaic industry is relying on silicon and its semiconductor properties. In contrast to its lower homologue, the carbon, silicon is capable of expanding its coordination geometry forming penta-, hexa- and even heptacoordinate complexes. Several of these structures have been examined over the last decades. However, most of these higher coordinate silicon complexes have been found to be hydrolytically unstable limiting their wider use, for instance in biological applications. The present thesis is addressing these limitations by investigating hexacoordinate (arenediolato)bis(polypyridyl)silicon(IV) complexes. The first part of the thesis deals with the synthesis and synthetic modification of higher coordinate silicon(IV) complexes. A successful post-coordination functionalization of silicon(IV) complexes is demonstrated. Besides halogenation, oxidation, and nitration reactions, a convenient nitrationreduction- condensation strategy tolerating various functional groups is discussed. Moreover, a synthetic approach to tris-heteroleptic complexes coordinating the DNA-intercalating ligand dppz is shown. In a prove of principal study, the results of the binding affinity of some silicon(IV) complexes to calf thymus DNA are presented. In a second project, the syntheses and biological properties of dinuclear metal-silicon(IV) complexes are studied. In order to constitute a small library of dinuclear complexes, different synthetic strategies including the previously presented nitration-reduction-condensation strategy, are discussed. With the library in hand, the biological activities of these complexes are investigated through binding studies to calf thymus DNA and G-quadruplex DNA. Moreover, the outcome of a cytotoxicity study using the MTT test for some dinuclear complexes is presented. In a third project, a Bodipy fluorophor is attached to the silicon(IV) complexes using various synthetic routes including the nitration-reduction-condensation strategy as well as a post-coordination clickchemistry approach. The photochemical and biological properties, namely the binding to calf thymus DNA and the light-switch behavior, of the obtained complexes are examined. Finally, the results of in-vitro confocal laser scanning microscope tests studying the ability of the complexes to enter the cell nucleus are shown