The Influence of the Alkylamino Group on the Solvatochromic Behavior of 5-(4-substituted-arylidene)-1,3-dimethylpyrimidine-2,4,6-triones: Synthesis, Spectroscopic and Computational Studies

Advances in electronics and medical diagnostics have made organic dyes extremely popular as key functional materials. From a practical viewpoint, it is necessary to assess the spectroscopic and physicochemical properties of newly designed dyes. In this context, the condensation of 1,3-dimethylbarbituric acid with electron-rich alkylaminobenzaldehyde derivatives has been described, resulting in a series of merocyanine-type dyes. These dyes exhibit intense blue-light absorption but weak fluorescence. An electron-donating alkylamino group at position C4 is responsible for the solvatochromic behavior of the dyes since the lone electron pair of the nitrogen atom is variably delocalized toward the barbituric ring, which exhibits electron-withdrawing properties. This was elucidated, taking into account the different geometry of the amino group. The intramolecular charge transfer in the molecules is responsible for the relatively high redshift in absorption and fluorescence spectra. Additionally, an increase in solvent polarity moves the absorption and fluorescence to lower energy regions. The observed solvatochromism is discussed in terms of the four-parameter Catalán solvent polarity scale. The differences in the behavior of the dyes were quantified with the aid of time-dependent density functional theory calculations. The obtained results made it possible to find regularities linking the basic spectroscopic properties of the compounds with their chemical structure. This is important in the targeted search for new, practically important dyes.

Design, Synthesis, and Spectral Properties of Novel 2-Mercaptobenzothiazole Derivatives

This paper is focused on the optimalization of methods for the synthesis, isolation, and purification of 2-mercaptobenzothiazole-based acrylic and methacrylic monomers. The structures of the newly synthesized compounds were confirmed through infrared (IR) and nuclear magnetic resonance spectroscopy (NMR). Spectroscopic properties of the resulting 2-mercaptobenzothiazole derivatives were determined based on their absorption spectra and molar absorption coefficients in solvents with varying polarities. A correlation was established between the calculated density functional theory (DFT) energies and Frontier Molecular Orbitals and the experimental observations, confirming their consistency. The practical utility of the synthesized compounds, particularly in future polymerization processes, hinges on a thorough understanding of these properties.

Structures and Spectroscopic Properties of Polysulfide Radical Anions: A Theoretical Perspective

The potential involvement of polysulfide radical anions Sn•- is a recurring theme in discussions of the basic and applied chemistry of elemental sulfur. However, while the spectroscopic features for n = 2 and 3 are well-established, information on the structures and optical characteristics of the larger congeners (n = 4-8) is sparse. To aid identification of these ephemeral species we have performed PCM-corrected DFT calculations to establish the preferred geometries for Sn•- (n = 4-8) in the polar media in which they are typically generated. TD-DFT calculations were then used to determine the number, nature and energies of the electronic excitations possible for these species. Numerical reliability of the approach was tested by comparison of the predicted and experimental excitation energies found for S2•- and S3•-. The low-energy (near-IR) transitions found for the two acyclic isomers of S4•- (C2h and C2v symmetry) and for S5•- (Cs symmetry) can be understood by extension of the simple HMO π-only chain model that serves for S2•- and S3•-. By contrast, the excitations predicted for the quasi-cyclic structures Sn•- (n = 6-8) are better described in terms of σ → σ* processes within a localized 2c-3e manifold.

(Ro)vibrational Spectroscopic Constants, Lifetime and QTAIM Evaluation of Fullerene Dimers Stability

The iconic caged shape of fullerenes gives rise to a series of unique chemical and physical properties; hence a deeper understanding of the attractive and repulsive forces between two buckyballs can bring detrimental information about the structural stability of such complexes, providing significant data applicable for several studies. The potential energy curves for the interaction of multiple van der Waals buckyball complexes with increasing mass were theoretically obtained within the DFT framework at ωB97xD/6-31G(d) compound model. These potential energy curves were employed to estimate the spectroscopic constants and the lifetime of the fullerene complexes with the Discrete Variable Representation and with the Dunham approaches. It was revealed that both methods are compatible in determining the rovibrational structure of the dimers and that they are genuinely stable, i.e., long-lived complexes. To further inquire into the nature of such interaction, Bader's QTAIM approach was applied. QTAIM descriptors indicate that the interactions of these closed-shell systems are dominated by weak van der Waals forces. This non-covalent interaction character was confirmed by the RDG analysis scheme. Indirectly, QTAIM also allowed us to confirm the stability of the non-covalent bonded fullerene dimers. Our lifetime calculations have shown that the studied dimers are stable for more than 1 ps, which increases accordingly with the number of carbon atoms.

Metal Complexes with Naphthalene-Based Acetic Acids as Ligands: Structure and Biological Activity

Naproxen (6-methoxy-α-methyl-2-naphthaleneacetic acid), 1-naphthylacetic acid, 2-naphthylacetic acid and 1-pyreneacetic acid are derivatives of acetic acid bearing a naphthalene-based ring. In the present review, the coordination compounds of naproxen, 1- or 2-naphthylacetato and 1-pyreneacetato ligands are discussed in regard to their structural features (nature and nuclearity of metal ions and coordination mode of ligands), their spectroscopic and physicochemical properties and their biological activities.

Synthesis, Experimental and Theoretical Study of Azidochromones

A series of 2-(haloalkyl)-3-azidomethyl and 6-azido chromones has been synthetized, characterized and studied by theoretical (DFT calculations) and spectroscopic methods (UV-Vis, NMR). The crystal structure of 3-azidomethyl-2-difluoromethyl chromone, determined by X-ray diffraction methods, shows a planar framework due to extended π-bond delocalization. Its molecular packing is stabilized by F···H, N···H and O···H hydrogen bonds, π···π stacking and C–O···π intermolecular interactions. Moreover, AIM, NCI and Hirshfeld analysis evidenced that azido moiety has a significant role in the stabilization of crystal packing through weak intermolecular interactions, where analysis of electronic density suggested closed-shell (CS) interatomic interactions.

Insight into the Effect of Counterions on the Chromatic Properties of Cr-Doped Rutile TiO2-Based Pigments

Rutile TiO₂ pigments codoped with chromophore ion Cr³⁺ and various charge-balancing ions (i.e., counterions species of Sb, Nb, W and Mo) were prepared by a solid-phase reaction method. The effects of the counterions and calcination temperatures on the phase structure, color-rendering and spectroscopic properties, microstructure, and stability of the synthesized pigments were investigated in detail. The results showed that the introduction of 5-10% counterions improved the solubility of Cr³⁺ in the TiO₂ lattice to form the single-phase rutile pigments calcined at 1100 °C for 2 h. The 10% Cr-doped pigment showed a dark brown color. Depending on the content and type of counterions, the color of the codoped pigments was tailored from yellow to reddish or yellowish-orange to black with different brightness and hue. The influence mechanism of counterions was ascribed to the lattice distortion and variation in the charge balance condition. It was found that the addition of Sb, Nb, or Mo resulted in a remarkable improvement in the NIR reflectance of pigments. The grain growth was inhibited with the codoping of Cr/Sb and Cr/Nb to achieve the nano-sized pigments. In addition, the prepared pigments exhibited good acid and alkali corrosion resistance as well as excellent stability and coloring performance in transparent ceramic glazes.

Cationic Exciplexes: Role of Hydrogen Bonding in Deactivation and Electronic Coupling

Emissive properties for the cationic exciplex (A⁺ */D→A^. D^.+ ) of an isoquinolinium cation tethered to a substituted arene (1⁺ ) are strongly affected by hydrogen bonding solvents. At equal dielectric constant (ϵ), the ground-to-excited state energy gaps (ΔG) and solvent reorganization energies (λ_s ) decrease from nitriles to aliphatic alcohols. The corresponding decrease from aliphatic alcohols to high hydrogen bond acidity solvents is ∼3 times larger. The exciplex decay (k_Ex ), largely determined by unfolding of the exciplex to a stretched conformer, changes in a complex way depending on the strength of the hydrogen bond ability of these solvents. In contrast, the electronic couplings between the exciplex ground, excited, and charge transfer states do not show a solvent functionality dependence.

Substituent and Solvent Polarity on the Spectroscopic Properties in Azo Derivatives of 2-Hydroxynaphthalene and Their Difluoroboranes Complexes

Novel fluorescent dyes such as difluoroborane complexes of 1-phenylazonaphthalen-2-ol derivatives were successfully synthesized and characterized with a focus on the influence of a substituent and a solvent on the basic photophysical properties. ¹H, ¹¹B, ¹³C, ¹⁵N, and ¹⁹F nuclear magnetic resonance (NMR) spectra of substituted 1-phenylazonaphthalen-2-ol difluoroboranes and their parent azo dyes were recorded and discussed. The absorption and emission properties of synthesized compounds were investigated in solvents of varying polarity. They were found to be fluorescent despite the presence of the azo group. The azo group rotation was blocked by complexing with -BF₂ to get a red shift in absorption. Solvent-dependent spectral properties of compounds were investigated using Lipper-Mataga and Bakhshiev plot. The calculated DFT energies and Frontier Molecular Orbitals calculations of the studied compounds were proved to be consistent with the experimental observations.

Enzymatic Browning in Wheat Kernels Produces Symptom of Black Point Caused by Bipolaris sorokiniana

To understand the blackening mechanism in black point diseased kernels, ultraviolet–visible light (UV–Vis) and Fourier-transform infrared (FT-IR) absorbance spectra of extracts made from the blackening parts of black point-affected (BP) kernels and the analogous part of black point-free (BPF) kernels were measured using susceptible wheat genotypes “PZSCL6” inoculated with Bipolaris sorokiniana (the dominant pathogen causing this disease). In addition, metabolite differences between BP and BPF kernels were identified by a method that combines gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-high resolution mass spectrometry (LC-MS). Successively, symptoms of black point were produced in vitro. The results showed (i) the spectroscopic properties of the extracts from BP and BPF kernels were very similar, with an absorption peak at 235 nm and a small shoulder at 280–300 nm in both UV–Vis spectra and shared vibrations at 3400–3300, 2925 and 2852, 1512 and 1463, 1709, 1220, 600–860 cm^–1 in FT-IR spectra that are consistent with similar bonding characteristics. In contrast, spectroscopic properties of extracts from wheat kernels were different from those of synthetic melanin and extracellular and intracellular melanin produced by B. sorokiniana. (ii) Levels of 156 metabolites in BP kernels were different from those in BPF kernels. Among those 156 metabolites, levels of phenolic acids (ferulic acid and p-coumaric acid), 11 phenolamides compounds, and four benzoxazinone derivatives were significantly higher in BP kernels than in BPF kernels. (iii) Symptom of black point could be produced in vitro in wheat kernels with supplement of phenol substrate (catechol) and H₂O₂. This result proved that blackening substance causing symptom of black point was produced by enzymatic browning in wheat kernels instead of by B. sorokiniana.

Substituted 2-Phenacylbenzoxazole Difluoroboranes: Synthesis, Structure and Properties

Novel fluorescent dyes such as benzoxazole-boron complexes, bearing β-ketoiminate ligands, have been synthesized and characterized with a focus on the influence of a substituent on the basic photophysical properties. ¹H, ¹¹B, ¹³C, ¹⁵N, and ¹⁹F nuclear magnetic resonance (NMR) spectra of substituted 2-phenacylbenzoxazole difluoroboranes have been recorded and discussed. It is worth mentioning that a high correlation coefficient was found between ¹⁵N-NMR parameters and substituent constants. The photophysical properties of these new dyes have been investigated by fluorescence and ultraviolet-visible (UV-Vis) absorption spectroscopy. The geometry optimization, vibrational spectra, and the HOMO and LUMO energies were calculated based on density functional theory with the use of the B3LYP functional and 6-311++G(d,p) basis set.

Spectroscopic Properties of Erbium-Doped Oxyfluoride Phospho-Tellurite Glass and Transparent Glass-Ceramic Containing BaF2 Nanocrystals

The ErF₃-doped oxyfluoride phospho-tellurite glasses in the (40-x) TeO₂-10P₂O₅-45 (BaF₂-ZnF₂) -5Na₂O-xErF₃ system (where x = 0.25, 0.50, 0.75, 1.00, and 1.25 mol%) have been prepared by the conventional melt-quenching method. The effect of erbium trifluoride addition on thermal, structure, and spectroscopic properties of oxyfluoride phospho-tellurite precursor glass was studied by differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR), and Raman spectroscopy as well as emission measurements, respectively. The DSC curves were used to investigate characteristic temperatures and thermal stability of the precursor glass doped with varying content of ErF₃. FTIR and Raman spectra were introduced to characterize the evolution of structure and phonon energy of the glasses. It was found that the addition of ErF₃ up to 1.25 mol% into the chemical composition of phospho-tellurite precursor glass enhanced 2.7 µm emission and upconversion. By controlled heat-treatment process of the host glass doped with the highest content of erbium trifluoride (1.25 mol%), transparent erbium-doped phospho-tellurite glass-ceramic (GC) was obtained. X-ray diffraction analysis confirmed the presence of BaF₂ nanocrystals with the average 16 nm diameter in a glass matrix. Moreover, MIR, NIR, and UC emissions of the glass-ceramic were discussed in detail and compared to the spectroscopic properties of the glass doped with 1.25 mol% of ErF₃ (the base glass).

BODIPY Dyes Bearing Multibranched Fluorinated Chains: Synthesis, Structural, and Spectroscopic Studies

A small series of boron-dipyrromethene (BODIPY) dyes, characterized by the presence of multibranched fluorinated residues, were designed and synthesized. The dyes differ in both the position (para-perfluoroalkoxy-substituted phenyl ring or boron functionalization) and number of magnetically equivalent fluorine atoms (27 or 54 fluorine atoms per molecule). Photophysical and crystallographic characterization of the synthesized BODIPYs was carried out to evaluate the effect of the presence of highly fluorinated moieties on the optical and morphological properties of such compounds.

Phosphorescent Modulation of Metallophilic Clusters and Recognition of Solvents through a Flexible Host-Guest Assembly: A Theoretical Investigation

MP2 (Second order approximation of Møller–Plesset perturbation theory) and DFT/TD-DFT (Density functional theory/Time-dependent_density_functional_theory) investigations have been performed on metallophilic nanomaterials of host clusters [Au(NHC)₂]⁺⋅⋅⋅[M(CN)₂]⁻⋅⋅⋅[Au(NHC)₂]⁺ (NHC = N-heterocyclic carbene, M = Au, Ag) with high phosphorescence. The phosphorescence quantum yield order of clusters in the experiments was evidenced by their order of μ_S1/ΔE_S1−T1 values (μS1: S₀ → S₁ transition dipole, ∆ES1−T1: splitting energy between the lowest-lying singlet S₁ and the triplet excited state T₁ states). The systematic variation of the guest solvents (S1: CH₃OH, S2: CH₃CH₂OH, S3: H₂O) are employed not only to illuminate their effect on the metallophilic interaction and phosphorescence but also as the probes to investigate the recognized capacity of the hosts. The simulations revealed that the metallophilic interactions are mainly electrostatic and the guests can subtly modulate the geometries, especially metallophilic Au⋅⋅⋅M distances of the hosts through mutual hydrogen bond interactions. The phosphorescence spectra of hosts are predicted to be blue-shifted under polar solvent and the excitation from HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) was found to be responsible for the ³MLCT (triplet metal-to-ligand charge transfer) characters in the hosts and host-guest complexes. The results of investigation can be introduced as the clues for the design of promising blue-emitting phosphorescent and functional materials.

Organozinc Precursor-Derived Crystalline ZnO Nanoparticles: Synthesis, Characterization and Their Spectroscopic Properties

Crystalline ZnO_-ROH and ZnO_-OR (R = Me, Et, iPr, nBu) nanoparticles (NPs) have been successfully synthesized by the thermal decomposition of in-situ-formed organozinc complexes Zn(OR)₂ deriving from the reaction of Zn[N(SiMe₃)₂]₂ with ROH and of the freshly prepared Zn(OR)₂ under an identical condition, respectively. With increasing carbon chain length of alkyl alcohol, the thermal decomposition temperature and dispersibility of in-situ-formed intermediate zinc alkoxides in oleylamine markedly influenced the particle sizes of ZnO_-ROH and its shape (sphere, plate-like aggregations), while a strong diffraction peak-broadening effect is observed with decreasing particle size. For ZnO_-OR NPs, different particle sizes and various morphologies (hollow sphere or cuboid-like rod, solid sphere) are also observed. As a comparison, the calcination of the fresh-prepared Zn(OR)₂ generated ZnO_-R NPs possessing the particle sizes of 5.4~34.1 nm. All crystalline ZnO nanoparticles are characterized using X-ray diffraction analysis, electron microscopy and solid-state ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy. The size effect caused by confinement of electrons’ movement and the defect centres caused by unpaired electrons on oxygen vacancies or ionized impurity heteroatoms in the crystal lattices are monitored by UV-visible spectroscopy, electron paramagnetic resonance (EPR) and photoluminescent (PL) spectroscopy, respectively. Based on the types of defects determined by EPR signals and correspondingly defect-induced probably appeared PL peak position compared to actual obtained PL spectra, we find that it is difficult to establish a direct relationship between defect types and PL peak position, revealing the complication of the formation of defect types and photoluminescence properties.

Synthesis of Fluorescent Core-Shell Metal Nanohybrids: A Versatile Approach

A flexible way of fabricating core-shell noble metal-organic nanohybrids with tailored chemical and spectroscopic properties is proposed here. The synthetic protocol consists of a multi-step procedure able to guarantee acceptable reproducibility of core size and shape as well as control of the organic outer layer. The proposed method highlights limitations in obtaining highly controllable products, although the heterogeneity degree of the nanostructures is in line with that expected from bottom-up approaches in solution. Selective functionalization of the nanohybrids with properly-substituted fluorescent dyes under variable experimental conditions allowed the preparation of composite systems of tunable spectroscopic properties to be employed as nanoprobes in sensing or photonic applications. To this end, preliminary investigation on embedding the nanohybrids in compatible polymeric matrices is also reported.

Syntheses, structures and properties of two new isostructural zinc(II) complexes based on 1-[(benzotriazol-1-yl)methyl]-1H-imidazole

Due to their strong coordination ability and the diversities of their coordination modes, N-heterocyclic organic compounds are used extensively as ligands for the construction of complexes with fascinating structures and potential applications in many fields. Two new complexes, namely bis{1-[(benzotriazol-1-yl)methyl]-1H-imidazole-κN³}dibromidozinc(II), [ZnBr₂(C₁₀H₉N₅)₂], (I), and bis{1-[(benzotriazol-1-yl)methyl]-1H-imidazole-κN³}diiodidozinc(II), [ZnI₂(C₁₀H₉N₅)₂], (II), have been synthesized by reaction of the unsymmetrical N-heterocyclic ligand 1-[(benzotriazol-1-yl)methyl]-1H-imidazole (bmi) with Zn(acetate)₂ in the presence of KBr or KI. Single-crystal X-ray diffraction analysis shows that both complexes exhibit a mononuclear structure, in which the bmi ligands coordinate to the central metal ion in a monodentate mode. In the solid state, both complexes possess a three-dimensional network formed by hydrogen bonds and π-π interactions. In addition, the IR spectroscopic properties, PXRD patterns and fluorescence properties of both complexes have been investigated.

Synthesis, crystal structure, and spectroscopic and thermal properties of the polymeric compound catena-poly[[bis(2,4-dichlorobenzoato)zinc(II)]-μ-isonicotinamide]

Zinc(II) carboxylates with O-, S- and N-donor ligands are interesting for their structural features, as well as for their antibacterial and antifungal activities. The one-dimensional zinc(II) coordination complex catena-poly[[bis(2,4-dichlorobenzoato-κO)zinc(II)]-μ-isonicotinamide-κ(2)N(1):O], [Zn(C7H3Cl2O2)2(C6H6N2O)]n, has been prepared and characterized by IR spectroscopy, single-crystal X-ray analysis and thermal analysis. The tetrahedral ZnO3N coordination about the Zn(II) cation is built up by the N atom of the pyridine ring, an O atom of the carbonyl group of the isonicotinamide ligand and two O atoms of two dichlorobenzoate ligands. Isonicotinamide serves as a bridge between tetrahedra, with a Zn···Zn distance of 8.8161 (7) Å. Additionally, π-π interactions between the planar benzene rings contribute to the stabilization of the extended structure. The structure is also stabilized by intermolecular hydrogen bonds between the amino and carboxylate groups of the ligands, forming a two-dimensional network. During thermal decomposition of the complex, isonicotinamide, dichlorobenzene and carbon dioxide were evolved. The final solid product of the thermal decomposition heated up to 1173 K was metallic zinc.

Synthesis, crystal structure and spectroscopic properties of trans-dibromidobis(2,2-dimethylpropane-1,3-diamine-κ(2)N,N')chromium(III) perchlorate

The title complex salt, trans-anti-[CrBr2(Me2tn)2]ClO4 (where Me2tn = 2,2-dimethylpropane-1,3-diamine, C5H14N2), was prepared and its structure determined by single-crystal X-ray diffraction at 100 K. The asymmetric unit contains three conformationally similar complex cations and three perchlorate anions. In each complex cation, the Cr(III) centre is coordinated by four N atoms of two chelating Me2tn ligands in the equatorial plane and by two Br atoms in a trans-axial arrangement, to give a distorted octahedral geometry. Interionic contacts are dominated by extensive hydrogen bonding, involving the NH groups of the Me2tn ligand as donors and the anion O atoms or coordinated Br atoms as acceptors, resulting in two-dimensional layers in the bc plane. Ligand field analysis based on the angular overlap model, and IR and electronic spectroscopic properties, are also discussed.

Density functional theory

Density functional theory (DFT) finds increasing use in applications related to biological systems. Advancements in methodology and implementations have reached a point where predicted properties of reasonable to high quality can be obtained. Thus, DFT studies can complement experimental investigations, or even venture with some confidence into experimentally unexplored territory. In the present contribution, we provide an overview of the properties that can be calculated with DFT, such as geometries, energies, reaction mechanisms, and spectroscopic properties. A wide range of spectroscopic parameters is nowadays accessible with DFT, including quantities related to infrared and optical spectra, X-ray absorption and Mössbauer, as well as all of the magnetic properties connected with electron paramagnetic resonance spectroscopy except relaxation times. We highlight each of these fields of application with selected examples from the recent literature and comment on the capabilities and limitations of current methods.