Substituents Research Articles

Molecular modeling of [VO(L1–4)(R)] complexes (R = bipyridine, phenanthroline): DFT study of antioxidant activity, DNA binding and evaluation of electron-donating and -withdrawing substituent groups

A DFT (density functional theory) study was conducted with eight oxovanadium complexes (C1 – C8) of general formula [VO(L1–4)(R)] (R = bipyridine, phenanthroline; L1–4 = group of ligands derived from dithiocarbamate). The obtained geometries showed a good correlation with the experimental structures. Molecular orbital analysis revealed that the contribution of the L-ligand in the SOMO (single-occupied molecular orbital) of the complexes correlated with the experimental antioxidant activity (IC50), while the contribution of the R-ligand to the LUMO (lowest unoccupied molecular orbital) of the complexes correlated with the experimental complex-DNA interaction (Kb). It has been identified that the presence of an electron-donating substituent group (such as –NH2) in the C5 – C6 structures should enhance these complexes' antioxidant and DNA interaction activities.

Effect of the substituents on luminescent behaviors of the salts based on 4,4′-(4-amino-4H-1,2,4-triazole-3,5-diyl)diphenol

To further exploit the new luminescent materials, three new salts containing 4-amino-1,2,4-triazole, namely, [HADO]+A– (A = BSA (1), MBA (2) and SBA (3), ADO = 4,4′-(4-amino-4H-1,2,4-triazole-3,5-diyl) diphenol, BSA = benzene sulfonic acid, MBA = p-toluene sulfonic acid, SBA = 2-hydroxybenzoic-5-sulfonic acid), have been successfully prepared by the reaction of ADO and a set of sulfonic acids, respectively. The luminescent maximal emission peaks can be found at 429, 434 and 461 nm for its salts 1–3 in the solid state at room temperature, respectively. Evidently, the order of luminescent peaks: 1<2<3, can be assigned to the substituent groups effect. Compared with the free ADO, the emission maxima of salts 1–3 are assuredly red-shifted about 27, 32 and 59 nm, respectively, suggesting that the emission bands are relevant to the intermolecular interactions. Compounds 1–3 were structurally characterized by X–ray single crystal diffraction, FT-IR spectroscopy and powder X-ray diffraction (PXRD). The results of single crystal X-ray diffraction analysis reveal that a set of hydrogen bonds of N/O/C–H⋯O could be observed. The Hirshfeld analysis indicates that the order of the C…C close contacts contribution can be observed to be 1<2<3, which can be responsible for that of the luminescent maxima. Additionally, the thermal behaviors of compounds 1–3 were investigated in detail.

Selective Photodynamic Activity of Tetrakis(4-aminophenyl)porphyrins with and without Acetyl Protecting Groups on Cancer and Normal Cells.

Tetrakis(4-aminophenyl)porphyrin (1) and tetrakis(4-acetamidophenyl)porphyrin (2) were dissolved in water with the incorporation of a polysaccharide (λ-carrageenan (CGN)) as a water-solubilizing agent. Although the photodynamic activity of the CGN-2 complex was considerably lower than that of the CGN-1 complex, the selectivity index (SI; IC50 in a normal cell/IC50 in a cancer cell) of the CGN-2 complex was considerably higher than that of the CGN-1 complex. This is because the photodynamic activity of the CGN-2 complex was significantly affected by the intracellular uptakes by the normal and cancer cells. During in vivo experiments, the CGN-2 complex inhibited tumor growth under light irradiation with high blood retention compared with the CGN-1 complex and Photofrin, which exhibited lower blood retention. This study showed that the photodynamic activity and SI are influenced by substituent groups of arene in the meso-positions of porphyrin analogs.

A Hammett's analysis of the substituent effect in functionalized diketopyrrolopyrrole (DPP) systems: Optoelectronic properties and intramolecular charge transfer effects.

Diketopyrrolopyrrole (DPP) systems have promising applications in different organic electronic devices. In this work, we investigated the effect of 20 different substituent groups on the optoelectronic properties of DPP-based derivatives as the donor ( )-material in an organic photovoltaic (OPV) device. For this purpose, we employed Hammett's theory (HT), which quantifies the electron-donating or -withdrawing properties of a given substituent group. Machine learning (ML)-based , , , , , , , and Hammett's constants previously determined were used. Mono- (DPP-X1 ) and di-functionalized (DPP-X2 ) DPPs, where X is a substituent group, were investigated using density functional theory (DFT), time-dependent DFT (TDDFT), and ab initio methods. Several properties were computed using CAM-B3LYP and the second-order algebraic diagrammatic construction, ADC(2), an ab initio wave function method, including the adiabatic ionization potential ( ), the electron affinity ( ), the HOMO-LUMO gaps ( ), and the maximum absorption wavelengths ( ), the first excited state transition 1 S0 → 1 S1 energies ( ) (the optical gap), and exciton binding energies. From the optoelectronic properties and employing typical acceptor systems, the power conversion efficiency ( ), open-circuit voltage ( ), and fill factor ( ) were predicted for a DPP-based OPV device. These photovoltaic properties were also correlated with the machine learning (ML)-based Hammett's constants. Overall, good correlations between all properties and the different types of constants were obtained, except for the constants, which are related to inductive effects. This scenario suggests that resonance is the main factor controlling electron donation and withdrawal effects. We found that substituent groups with large values can produce higher photovoltaic efficiencies. It was also found that electron-withdrawing groups (EWGs) reduced and considerably compared to the unsubstituted DPP-H. Moreover, for every decrease (increase) in the values of a given optoelectronic property of DPP-X1 systems, a more significant decrease (increase) in the same values was observed for the DPP-X2 , thus showing that the addition of the second substituent results in a more extensive influence on all electronic properties. For the exciton binding energies, an unsupervised machine learning algorithm identified groups of substituents characterized by average values (centroids) of Hammett's constants that can drive the search for new DDP-derived materials. Our work presents a promising approach by applying HT on molecular engineering DPP-based molecules and other conjugated molecules for applications on organic optoelectronic devices.

Evaluation of nonnatural L-iminosugar C,C-glycosides, a new class of C-branched iminosugars, as glycosidase inhibitors

Capitalizing on a previously developed Staudinger/azaWittig/Grignard (SAWG)-ring contraction sequence that furnished protected six-membered L-iminosugar C,C-glycosides bearing an allyl group and various substituents at the pseudoanomeric position, the synthesis and glycosidase inhibition of a small library of six- and seven-membered L-iminosugar C,C-glycosides is reported. Their hydrogenolysis or cyclization by RCM followed by deprotection afforded eleven L-iminosugars including spirocyclic derivatives. All compounds adopt a 1C4 conformation in solution according to NMR data. Compared to previously reported branched L-iminosugars, the L-iminosugar C,C-glycosides reported herein were less potent glycosidase inhibitors. However, some of these compounds showed micromolar inhibition of human lysosome β-glucocerebrosidase suggesting that such iminosugars could be useful to access potent CGase inhibitors by adjusting the structure/length of the pseudoanomeric substituents.

Synthesis, characterization, luminescence and NLO properties of heterotrinuclear MII-RuII-MII (M=Ni/Zn) complexes composed of coordination and organometallic sites

A new series of heterotrinuclear complexes of the type [Ru(dppm)2((CCC6H4CCC6H3 (O)HCNC6H4X)Ni(L'))2] (1a-c) and [Ru(dppm)2((CCC6H4CCC6H3(O)HCNC6H4X)Zn(L'))2] (2a-c) were prepared by the reaction of trans-[Ru(dppm)2(CCC6H4CCC6H3(OH)HCNC6H4X)2] with Ni(II)/Zn(II) ions in presence of 8-hydroxyquinoline. (where, X= Cl, Br, I; L'= 8-hydroxyquinoline) All the complexes were characterized by elemental analysis, FT-IR, 1H NMR, ESI-MS, UV–visible and thermogravimetric studies. The electrochemical properties of all the complexes indicate quasireversible redox behaviour corresponding to Ru(II)-Ru(III) and Ni(II)/ Ni(III) for 1a-c and Ru(II)/Ru(III) for 2a-c and are susceptible to variation of substituent group on ligand. All complexes show room temperature luminescence corresponding to π→π* intraligand charge transfer (ILCT) transition. The emission wavelength of the complexes is finely tuned by increasing π-conjugation and variation of substituent groups in the complexes. The second harmonic generation (SHG) efficiency of the complexes was measured by Kurtz-powder technique indicating that all complexes displayed the second harmonic generation (SHG) property.

Effect of Substituents on Molecular Reactivity during Lignin Oxidation by Chlorine Dioxide: A Density Functional Theory Study.

Lignin is a polymer with a complex structure. It is widely present in lignocellulosic biomass, and it has a variety of functional group substituents and linkage forms. Especially during the oxidation reaction, the positioning effect of the different substituents of the benzene ring leads to differences in lignin reactivity. The position of the benzene ring branched chain with respect to methoxy is important. The study of the effect of benzene substituents on the oxidation reaction's activity is still an unfinished task. In this study, density functional theory (DFT) and the m062x/6-311+g (d) basis set were used. Differences in the processes of phenolic oxygen intermediates formed by phenolic lignin structures (with different substituents) with chlorine dioxide during the chlorine dioxide reaction were investigated. Six phenolic lignin model species with different structures were selected. Bond energies, electrostatic potentials, atomic charges, Fukui functions and double descriptors of lignin model substances and reaction energy barriers are compared. The effects of benzene ring branched chains and methoxy on the mechanism of chlorine dioxide oxidation of lignin were revealed systematically. The results showed that the substituents with shorter branched chains and strong electron-absorbing ability were more stable. Lignin is not easily susceptible to the effects of chlorine dioxide. The substituents with longer branched chains have a significant effect on the flow of electron clouds. The results demonstrate that chlorine dioxide can affect the electron arrangement around the molecule, which directly affects the electrophilic activity of the molecule. The electron-absorbing effect of methoxy leads to a low dissociation energy of the phenolic hydroxyl group. Electrophilic reagents are more likely to attack this reaction site. In addition, the stabilizing effect of methoxy on the molecular structure of lignin was also found.

Size‐ and Emission‐Controlled Synthesis of Full‐Color Luminescent Metal‐Organic Frameworks for Tryptophan Detection

AbstractThe development of nanoscaled luminescent metal–organic frameworks (nano‐LMOFs) with organic linker‐based emission to explore their applications in sensing, bioimaging and photocatalysis is of great interest as material size and emission wavelength both have remarkable influence on their performances. However, there is lack of platforms that can systematically tune the emission and size of nano‐LMOFs with customized linker design. Herein two series of fcu‐ and csq‐type nano‐LMOFs, with precise size control in a broad range and emission colors from blue to near‐infrared, were prepared using 2,1,3‐benzothiadiazole and its derivative based ditopic‐ and tetratopic carboxylic acids as the emission sources. The modification of tetratopic carboxylic acids using OH and NH2 as the substituent groups not only induces significant emission bathochromic shift of the resultant MOFs, but also endows interesting features for their potential applications. As one example, we show that the non‐substituted and NH2‐substituted nano‐LMOFs exhibit turn‐off and turn‐on responses for highly selective and sensitive detection of tryptophan over other nineteen natural amino acids. This work sheds light on the rational construction of nano‐LMOFs with specific emission behaviours and sizes, which will undoubtedly facilitate their applications in related areas.

Size- and Emission-Controlled Synthesis of Full-Color Luminescent Metal-Organic Frameworks for Tryptophan Detection.

The development of nanoscaled luminescent metal-organic frameworks (nano-LMOFs) with organic linker-based emission to explore their applications in sensing, bioimaging and photocatalysis is of great interest as material size and emission wavelength both have remarkable influence on their performances. However, there is lack of platforms that can systematically tune the emission and size of nano-LMOFs with customized linker design. Herein two series of fcu- and csq-type nano-LMOFs, with precise size control in a broad range and emission colors from blue to near-infrared, were prepared using 2,1,3-benzothiadiazole and its derivative based ditopic- and tetratopic carboxylic acids as the emission sources. The modification of tetratopic carboxylic acids using OH and NH2 as the substituent groups not only induces significant emission bathochromic shift of the resultant MOFs, but also endows interesting features for their potential applications. As one example, we show that the non-substituted and NH2 -substituted nano-LMOFs exhibit turn-off and turn-on responses for highly selective and sensitive detection of tryptophan over other nineteen natural amino acids. This work sheds light on the rational construction of nano-LMOFs with specific emission behaviours and sizes, which will undoubtedly facilitate their applications in related areas.

Development of Novel Phase-Change Materials Derived from Methoxy Polyethylene Glycol and Aromatic Acyl Chlorides.

In this research, novel, organic, solid-liquid phase-change materials (PCMs) derived from methoxy polyethylene glycol (MPEG) and aromatic acyl chlorides (ACs) were prepared through a condensation reaction. The MPEGs were used as phase-change functional chains with different molecular weights (350, 550, 750, 2000, and 5000 g/mol). The aromatic ACs, terephthaloyl chloride (TPC) and isophthaloyl chloride (IPC), were employed as bulky linker cores. Solubility tests demonstrated that this family of PCMs is soluble in protic polar solvents such as H2O and MeOH, and insoluble in nonpolar solvents such as n-hexane. Fourier-ransform infrared spectroscopy (FT-IR UATR) and nuclear magnetic resonance (1H, 13C, DEPT 135°, COSY, HMQC, and HMBC NMR) were used to confirm the bonding of MPEG chains to ACs. The crystalline morphology of the synthesized materials was examined using polarized optical microscopy (POM), revealing the formation of spherulites with Maltese-cross-extinction patterns. Furthermore, it was confirmed that PCMs with higher molecular weights were crystalline at room temperature and exhibited an increased average spherulite size compared to their precursors. Thermal stability tests conducted through thermogravimetric analysis (TGA) indicated decomposition temperatures close to 400 °C for all PCMs. The phase-change properties were characterized by differential scanning calorimetry (DSC), revealing that the novel PCMs melted and crystallized between -23.7 and 60.2 °C and -39.9 and 45.9 °C, respectively. Moreover, the heat absorbed and released by the PCMs ranged from 57.9 to 198.8 J/g and 48.6 to 195.6 J/g, respectively. Additionally, the PCMs exhibited thermal stability after undergoing thermal cycles of melting-crystallization, indicating that energy absorption and release occurred at nearly constant temperatures. This study presents a new family of high-performance organic PCMs and demonstrates that the orientation of substituent groups in the phenylene ring influences supercooling, transition temperatures, and thermal energy storage capacity depending on the MPEG molecular weight.

The effect of substituent group in allyl benzoxazine on the thermal, mechanical and dielectric properties of modified bismaleimide

Allyl benzoxazine resin (BOZ-A) synthesized from 2,2′-diallyl bisphenol A (DABPA), aniline and paraformaldehyde has been used to improve the mechanical and processing properties of bismaleimide resin. However, the lower heat resistance and the unsatisfactory dielectric properties cannot satisfy the requirements of high-performance composites in aerospace fields. Introducing nonpolar materials into the resin matrix effectively improves the dielectric properties. Inspired by the designability of benzoxazine, a novel allyl benzoxazine resin grafted with trifluoromethyl (BOZ-F) or methyl (BOZ-C) was synthesized and blended with BD-type bismaleimide resin (BDM-C and BDM-F) to explore the effect of substituent groups on the comprehensive performance. Due to the different electronic effects of the substituents, BDM-C possesses higher reactivity with a polymerization temperature of 212.7 °C, which is lower than that of BDM-A (217.8 °C) and BDM-F (226.6 °C). Their respective reactivity also leads to differences in rheological properties. Specifically, BDM-F exhibited the excellent thermal stability with a Tg of 308.3 °C, which is 17.2 °C higher than that of BDM-A. Furthermore, the dielectric constant (Dk) and dielectric loss (Df) of BDM-F at 10.5 GHz decreased to 3.06 and 0.0078 from 3.13 and 0.0114 when compared with BDM-A. In addition, BDM-C demonstrated the highest bending strength of 136.02 MPa. The current study delivers an effective approach to balance the performance of thermosetting resins by regulating substituents, which is valuable for potential application in wave-transparent fields.

Reduction of four bis‐azo dyes by pig liver microsomal fraction in anaerobic conditions

AbstractThe study of azo dyes degradation products and their harmfulness is an important topic because their diffusion in the environment is still a serious problem. We investigated the reduction by pig liver microsomal fraction of four bis‐azo dyes, Acid Red 73, Acid Red 150, Direct Red 24, and Direct Red 28, in anaerobic condition. These complex molecules, different for position/nature of substituent groups and for the group interposed between the two azo bonds, allowed to investigate the correlation between substrate molecular structure and action of a subcellular fraction representative of the xenobiotic degradation by a living organism and the consequent possible appearance of harmful reaction products. Dyes were first carefully purified to eliminate interferences in the enzymatic assays. The reduction products were identified by gas chromatography/mass spectrometry. Acid Red 73 and Acid Red 150 were markedly reduced with production of harmful aromatic amines, while Direct Red 24 and Direct Red 28 were neither reduced to their synthesis amines nor to other amines. These results suggest that azo dyes with a benzidine derivative group are not degraded by microsomal fraction and therefore molecules with a similar structure could be classified with a lower risk index not producing any harmful catabolic product.

Substituent effect on the intramolecular hydrogen bond and the proton transfer process in pyrimidine azo dye : A computional study

This study provides a complete analysis of the electronic and photophysical properties of, the derivative of uracil, IsoOrotic (IOA) azo dyes. The ability of the dye to work as an excited state intramolecular proton transfer (ESIPT) was investigated by using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) methods. The effect of electron-donating substituents (CH3 and NMe2) and an electron-withdrawing one (NO2) was examined. In addition, the effect of the solvent polarity on the ESIPT process is studied. All the geometrical structures in the singlet ground (S0) and excited (S1) states, were optimized using B3LYP/6–311 + G** level of theory. The intramolecular hydrogen bond parameters (IHBs), and the Infra-Red vibrational analysis of the O-H bond show that the IHBs are enhanced in the S1 state. Furthermore, the absorption and emission spectra were simulated and the values of stokes shifts were observed. The PAIOA derivative with an electron withdrawing group shows large stokes shift compared with those having electron-donating ones. Therefore, we can safely conclude that the substituent groups and the different solvents are extremely impactful on the ESIPT process.

Spectroscopic and DFT study of tris(β-diketonato)cobalt(III) complexes

Nuclear magnetic resonance measurements confirm that, as expected, the mer isomer of tris(β-diketonato) cobalt(III) complexes is more stable ( mer isomers are more stable because they are less affected by steric hindrance and they have lower dipoles). An excess of the mer isomer or only the mer isomer is experimentally observed. The existence of both fac and mer isomers is predicted by density functional theory calculations. At room temperature, the nuclear magnetic resonance peaks of phenyl-containing mer complexes are broad due to the intermediate rotation of bulky phenyl groups resulting in only the average orientation of the non-equivalent protons in the mer complexes. However, upon heating to 55 °C (thus speeding up the rotation) or cooling to −50 °C (slowing down the rotation), this broad peak is resolved into three sets of carbon peaks appearing in the 13C NMR spectrum, as well as splitting of the 1H NMR peaks for the non-equivalent protons in the mer isomer. In solid-state 13C NMR the aromatic rings do not rotate, resulting in the splitting of all the 13C NMR peaks. Two sets of well-defined peaks are observed for the fluorine-containing compound [Co(CF3COCHCOCPh)3] in both the 13C and 19F NMR spectra, indicating that both the fac and mer isomers are present with a ratio of fac:mer = 0.1:1. The X-ray photoelectron spectroscopy measured binding energy of the Co 2p3/2 photoelectron lines are influenced by the subtle electronic (electron-donating or electron-withdrawing) properties of the R groups on the β-diketonato ligands. Various relationships are established between the binding energy of Co 2p3/2 and several physical and density functional theory–calculated properties, confirming good electronic communication (the measurable electronic effect that a molecular fragment has on the physical properties of another molecular fragment in the molecule) of the substituent groups through the pseudo aromatic system of the β-diketonato backbones to the metal.

Electron-modulating effects of intercalating molecules in functionalized graphene oxide: Optimizing the coordination microenvironment of Ag nanoparticles for efficient catalytic A3 coupling reactions

In this paper, functionalized graphene oxide (GO) nanosheets were modified by forming benzamide (BzA) bonds using aniline with different substituents (4-tertbutylaniline, 4-nitroaniline, aniline) as intercalating molecules. Then the Ag@R-BzA/GO composite catalysts were prepared by loading Ag nanoparticles to reveal the electronic modulation of functionalized graphene oxide interfaces by aniline molecules effects with different substituents. The experimental results showed that the layer spacing of the composites obtained after intercalation with aniline whose substituent is an electron-giving group increased by about 40%. Moreover, the electron donating role of tert‑butyl regulates the charge distribution on the graphene oxide material and provides a good coordination environment for the loading of Ag nanoparticles. AgNPs are stably present in the interlayer of graphene oxide nanosheets by ligating with amide bonds and oxygen-containing functional groups to produce strong metal-carrier interactions. Ag@4‑tert-BzA/GO composites showed high catalytic activity in the A3 coupling reaction of aldehydes, alkynes and amines for the synthesis of alkynylamines(TON=19225.82). The electronic effect of the substituent groups on the intercalated molecules reported in this paper is a modulation on the molecular and atomic scale, which provides a new idea for the modulation of the microenvironment in metal-loaded catalysts.

Substituent effect on photophysical properties and proton transfer process of HBQ derivatives

AbstractBackgroundIn view of the potential applications of 10‐hydroxybenzo [h] quinoline (HBQ) in biological probes and organic light‐emission devices, the excited state intramolecular proton transfer (ESIPT) mechanism of HBQ was investigated theoretically in the work.AimsIn order to give a detailed reaction mechanism, the ESIPT of molecular system with hydrogen bond is systematically studied using density functional theory and density functional theoryMethodsUsing density functional theory (DFT) and time‐dependent density functional theory (TDDFT), we investigate the photophysical properties and excited state proton transfer of 10‐hydroxybenzo [h] quinoline (HBQ)derivatives.ResultsThe optimized structure shows that HBQ1 and HBQ2 have no stable structure in S1 state. The analysis of bond length parameters and infrared vibration spectroscopy proved that the substituent groups regulated the hydrogen bond strength in the S0 state.ConclusionTherefore, substitution position will affect the excited state intramolecular proton transfer and the photophysical properties of the molecule.

Effect of Substituent Groups on the Strength of Intramolecular Hydrogen Bonds in 2,4-Dihydroxybenzophenone UV Absorbers

2,4-Dihydroxybenzophenone is the most widely used molecule in the benzophenone group of UV absorbers. It is known that the UV absorption ability is dependent on the substituents. Numerous studies have shown that the strength of intramolecular hydrogen bonds is the main factor affecting this type of UV absorber. However, the effect of substituents on the formation and nature of the hydrogen bonds has not been well studied. In this work, the effect of the type of substituent and the substitution position on the absorption intensity of 2,4-dihydroxybenzophenone molecules is verified both experimentally and theoretically. The effect of substituents on the intramolecular hydrogen bonding of 2,4-dihydroxybenzophenone was investigated by DFT calculations. The results indicate that the addition of different substituents leads to various changes in the strength of the hydrogen bonding in 2,4-dihydroxybenzophenone. On the X-substitution site or the Y-substitution site, halogen groups and electron-absorbing groups such as -CN and -NO2 increase the strength of the hydrogen bond, while electron-giving groups such as -N(CH3)2 and -OCH3 decrease the strength of the bond. For the same substituent, the one at the Y site has a higher effect on hydrogen bonding than that at the X site. By NBO analysis, it was found that the substituents would cause charge redistribution of the individual atoms of 2,4-dihydroxybenzophenones, thus affecting the formation and strength of the hydrogen bonds. Moreover, when the substituent is at the Y substitution site, the oxygen atom of the carbonyl group is less able to absorb electrons and more charge is attracted to the oxygen atom of the hydroxyl group, resulting in a larger charge difference between the two oxygen atoms and an increase of bond energy. Finally, a multiple linear regression analysis of the NPA charge number of the atoms involved in the formation of the hydrogen-bonded chelated six-membered ring was performed with the energy of the hydrogen bond and the percentage of influencing factors estimated, which were found to jointly affect the strength of hydrogen bonding. The aim of this study is to provide theoretical guidance for the design of benzophenone-based UV absorbers that absorb UV light of specific wavelength bands.

Fabrication of Schottky Barrier Diodes Utilizing Schiff Base Compounds and Metal Complexes with Schiff Base Ligands

AbstractFabrications of different kinds of diodes with various types of materials are the trends of modern research. In recent times organic materials and metal complexes containing organic ligands are chosen preferably for the fabrication of Schottky barrier diodes. Utilizations of Schiff‐base compounds and Schiff base containing metal complexes in the making of Schottky barrier diodes are immensely appreciated because the syntheses of Schiff‐base compounds are quite straightforward, less expensive and require less time. Large scale production of Schiff base materials is comparatively easier because their syntheses involve facile condensation reaction and their optical properties can be easily tuned by introducing simple substituent groups. Designing appropriate molecular structure plays pivotal role in the conducting properties of the materials. The molecular systems with exiting conducting properties can be utilized for the fabrication of such active electronic device. Sometimes, the specific structural arrangements enhance the charge flow upon illumination of light. These materials can be used in making photosensitive diode devices. In this context, this review, comprising of a collection of research articles regarding Schottky diode device based on Schiff bases and metal complexes with Schiff base ligands, may be helpful for the researchers of the relevant field.

Effect of an amine functionalization of phenanthroline ligand associated with an ester-pyridine ligand on excited-state properties of Re(I) complex. Interplay between two 3MLCT

In this work, the synthesis, characterization and photophysical properties of rhenium(I) polypyridyl compound, fac-[Re(et-isonic)(NH2phen)(CO)3]PF6, where NH2phen = 5-amino-1,10-phenanthroline and et-isonic = ethyl isonicotinate, are reported. The compound exhibited a broad absorption band around 300–500 nm that by Time-Dependent Density Functional Theory (TD-DFT) corresponds to a mixture of ILNH2phen and MLCTRe→NH2phen transitions and a contribution of the charge transfer transition MLCTRe→et-isonic. Contrary to what is expected, the change of Cl (λmax = 490 and 565 nm; ϕ = 0.002; τ = 0.49 ± 0.07 μs and < 0.020 μs) for et-isonic ligand (λmax = 590 nm; ϕ = 0.003; τ = 0.43 ± 0.03 μs and 0.044 ± 0.014 μs), a π-acceptor ligand, promoted a bathochromic shift of the emission maxima in acetonitrile solution. This distinct behavior can be rationalized in terms of the inversion of the lowest-lying excited state of the usual observed MLCTRe→NN to the unusual MLCTRe→et-isonic. On the other hand, the contribution of ligand-based excited state in the deactivation process cannot be ruled out. Additionally, as a triplet emitter, a high quantum yield for the singlet oxygen generation (0.50 ± 0.03) can be associated with either, 3MLCT or a 3LC state. The photophysics ally to the higher singlet oxygen generation reported herein provides new fundamental insights into the understanding of substituent groups on the polypyridyl ligands that are relevant to the practical development of the scientific field.

Controlling the Diradical Character of Thiele Like Compounds

Organic diradicals play an important role in many fields of chemistry, biochemistry, and materials science. In this work, by means of high-level theoretical calculations, we have investigated the effect of representative chemical substituents in p-quinodimethane (pQDM) and Thiele's hydrocarbons with respect to the singlet-triplet energy gap, a feature characterizing their diradical character. We show how the nature of the substituents has a very important effect in controlling the singlet-triplet energy gap so that several compounds show diradical features in their ground electronic state. Importantly, steric effects appear to play the most determinant role for pQDM analogues, with minor effects of the substituents in the central ring. For Thiele like compounds, we found that electron-withdrawing groups in the central ring favor the quinoidal form with a low or almost null diradical character, whereas electron-donating group substituents favor the aromatic-diradical form if the electron donation does not exceed 6-π electrons. In this case, if there is an excess of electron donation, the diradical character is reduced. The electronic spectrum of these compounds is also calculated, and we predict that the most intense bands occur in the visible region, although in some cases characteristic electronic transition in the near-IR region may appear.