CN Substituents Research Articles

Designing potentially singlet fission materials with an anti-Kasha behaviour.

Singlet fission (SF) compounds offer a promising avenue for improving the performance of solar cells. Using TD-DFT methods, anti-Kasha azulene derivatives that could carry out SF have been designed. For this purpose, substituted azulenes with a donor (-OH) and/or an acceptor group (-CN) have been systematically studied using the S2 ≥ 2T1 formula. We have found that -CN (-OH) substituents on electrophilic (nucleophilic) carbons result in improved SF properties when compared to azulene.

The Synthesis and Crystal Structures of New One- and Two-Dimensional Fe(II) Coordination Polymers Using Imidazole Derivatives

We studied the synthesis and crystal structures of a new two-dimensional (2D) coordination polymer, {FeII(1-Ethyl-imidazole)2[NiII(CN)4]}n (1), and one-dimensional (1D) coordination polymers, {FeII(1-benzyl-imidazole)4[NiII(CN)4]}n (2) and {FeII(1-Allyl-imidazole)4[NiII(CN)4]}n (3). Compound 1 has a 2D sheet structure, which is a traditional Hofmann-like structure. In compound 1, an octahedral FeII ion is coordinated with the nitrogen atoms of the [NiII(CN)4] planar unit at equatorial positions and monodentate imidazole derivatives at axial positions. The layers construct a parallel stacking array. Compounds 2 and 3 have a 1D chain structure. In compounds 2 and 3, the FeIIN6 coordination environment is formed with four imidazole ligands and two [NiII(CN)4]2− metalloligands. In the [NiII(CN)4]2− unit, two CN substituents act as bidentate ligands that form infinite –Ni–C–N–Fe–N–C–Ni– chains. Herein, we discuss the systematic design of polymeric dimensionality.

Mechanofluorochromic properties of 1-phenylanthracene derivatives with extremely simple structures

Several types of 1-phenylanthracene derivatives 1–4 were prepared and their photophysical properties were observed in the solution and solid states. Interestingly, the fluorine-substituted 1-phenylanthracene derivative 1c was found to exhibit a higher fluorescence quantum yield (Φf=0.57) in the solid state than in the solution state, probably due to the formation of intermolecular Ar–F•••H–Ar hydrogen bonds. Additionally, some of the 1-phenylanthracene derivatives exhibited mechanofluorochromic properties depending on the substituents of the phenyl group, with the derivatives having CF3, OMe, and CN substituents (1d-1f, 2, 3) showing a significant change in luminous color from a bluish to greenish color at “room temperature” after grinding. However, no change in the luminous color was observed for the derivatives having H, Me, and F substituents (1a-1c) at “room temperature” but luminous color change was observed with low temperature grinding (−78 °C), especially for the CN substituent, in which a significant change in the luminous color was observed at “room temperature” probably due to the formation of Ar-CN•••H–Ar hydorogen bond interactions. Interestingly, for the 1-phenylanthracene derivative 3 substituted with two CN groups, which exhibited a solvatochromic phenomenon, the luminous color recovered with controllable rate from green to bluish when heated and fumed with solvent vapor in the solid state, and the luminous color change with controllable recovery rate was repeatedly successfully observed. These anthracene derivatives have extremely simple structures and could probably be applied as new mechanofluorochromic materials.

Photophysical, electrochemical and electrochromic behavior of transition metal complexes with 1,10-phenanthroline ligands

A series of non-noble transition metal complexes were synthesized by coordinating Fe2+, Co2+, and Ni2+ with ligands having a parent structure of 4,7-diphenyl-1,10-phenanthroline (L1 and L2) and dipyrido[3,2-a:2′,3′-c]phenazine (L3–L5), and their photophysical, electrochemical, and electrochromic properties were studied. Both transition metal ions and ligands produce more or less influence on these properties. Electrochromic properties such as color, optical contrast, response time, coloration efficiency and switching stabilities can be tuned by selecting proper metal ions, parent structure of ligands, and substituent groups. Theory calculation results indicate that electrons flow from the metallic center to the ligands. The UV–vis spectra of all five Fe(II) complexes showed a broad and strong MLCT band at ca. 530 nm. The UV–vis spectra of Fe(II), Co(II) and Ni(II) complexes with L2 ligand showed a strong LC (π–π*) band at ca. 325 nm. Electrochromic process caused a change in the intensity of LC and MLCT absorption. The ligands produced little effect on the bleached and colored states of Fe(II) complexes, all of them showed a bleached state of red and a colored state of purple-red probably due to the reversible Fe(II)/Fe(III) transition. Both Co(II) and Ni(II) complexes showed a bleached state of pale yellow, however, the ligands produced significant effect on their colored states probably due to the partially electron density displacement between the metal ions and the ligands. When the parent structure of ligand is 4,7-diphenyl-1,10-phenanthroline, electron-donating substituent such as –OCH3 is beneficial to electrochromic properties, and Fe(II) complexes have higher optical contrast and coloration efficiency compared to Co(II) and Ni(II) complexes. When the parent structure of ligand is dipyrido[3,2-a:2′,3′-c]phenazine, –CN substituent markedly enhances the optical contrast and coloration efficiency of Fe(II), Co(II) and Ni(II) complexes.

Lifetime evaluation of thermally activated delayed fluorescence materials according to the positions of CN substituents

Lifetime evaluation of thermally activated delayed fluorescence materials according to the positions of CN substituents

Investigating the potential of organic semiconductor materials by DFT and TD-DFT calculations on aNDTs

The effects of substituting electron withdrawing and electron donating functional groups on the electronic and optical properties of angular naphthodithiophene (aNDT) were studied. Substitutions were made to the aNDT molecule at position 2 and 7, respectively. The computed ionization parameters and reorganisation energies distinguished between the p-type and n-type semiconducting natures of the unsubstituted aNDT molecule and those with the –C2H5, –OCH3, –NO2, and –CN substituents. However, the aNDT molecule with C2H5 as a substitution showed p-type behaviour since it had the largest electron reorganisation energy of about 0.37 eV. The ambipolar semiconducting property of methoxy [–OCH3–] substituted aNDT molecule was revealed from the RMSD value of 0.03 Å for both positive and negative charges with respect to neutral geometry. The absorption spectra differ significantly from those of unsubstituted aNDT, which reveals the impact of functional group substitution that changes the energy level of the molecules. The maximum absorption (λmax) and oscillator strength (f) at the excited states in vacuum was investigated using time dependent density functional theory (TD-DFT). The aNDT with electron withdrawing group [-NO2] substitution has a maximum absorption wavelength of 408 nm. Studying the intermolecular interactions between aNDT molecules was also accomplished with the help of Hirshfeld surface analysis. The current work provides insight into the development of novel organic semiconductors.

4,4′-Dicyano- versus 4,4′-Difluoro-BODIPYs in Chemoselective Postfunctionalization Reactions: Synthetic Advantages and Applications

The presence of F or CN substituents at boron in BODIPYs causes a dramatic effect on their reactivity, which allows their chemoselective postfunctionalization. Thus, whereas 1,3,5,7-tetramethyl B(CN)2-BODIPYs displayed enhanced reactivity in Knoevenagel condensations with aldehydes, the corresponding BF2-BODIPYs can experience selective aromatic electrophilic substitution (SEAr) reactions in the presence of the former. These (selective) reactions have been employed in the preparation of BODIPY dimers and tetramers, with balanced fluorescence and singlet oxygen formation, and all-BODIPY trimers and heptamers, with potential application as light-harvesting systems.

Substituent Effects in Tetrel Bonds Involving Aromatic Silane Derivatives: An ab initio Study.

In this manuscript substituent effects in several silicon tetrel bonding (TtB) complexes were investigated at the RI-MP2/def2-TZVP level of theory. Particularly, we have analysed how the interaction energy is influenced by the electronic nature of the substituent in both donor and acceptor moieties. To achieve that, several tetrafluorophenyl silane derivatives have been substituted at the meta and para positions by several electron donating and electron withdrawing groups (EDG and EWG, respectively), such as -NH2, -OCH3, -CH3, -H, -CF3 and -CN substituents. As electron donor molecules, we have used a series of hydrogen cyanide derivatives using the same EDGs and EWGs. We have obtained the Hammett's plots for different combinations of donors and acceptors and in all cases we have obtained good regression plots (interaction energies vs. Hammet's σ parameter). In addition, we have used the electrostatic potential (ESP) surface analysis as well as the Bader's theory of atoms in molecules (AIM) and noncovalent interaction plot (NCI plot) techniques to further characterize the TtBs studied herein. Finally, a Cambridge Structural Database (CSD) inspection was carried out, retrieving several structures where halogenated aromatic silanes participate in tetrel bonding interactions, being an additional stabilization force of their supramolecular architectures.

Enhanced n‐Type Thermoelectric Performance of Conjugated Polymers Based on an Indandione‐Terminated Quinoidal Unit through Comonomer Optimization

Comprehensive SummaryConjugated polymers (CPs) containing quinoidal units are promising in n‐type organic thermoelectric materials because of their deep‐positioned lowest unoccupied molecular orbital (LUMO) energy levels and planar conjugated backbones. Herein, three CPs have been synthesized by copolymerizing an indandione‐terminated quinoidal unit with bithiophene derivatives. Owning to the high electron affinity of the indandione‐terminated quinoidal unit, all polymers showed deep LUMO energy levels below –4.10 eV. Incorporating electron‐withdrawing substituents (F or CN) on the bithiophene comonomer can further downshift the LUMO energy levels. As a result, a more efficient n‐doping process can be realized when employing 4‐(2,3‐dihydro‐1,3‐dimethyl‐1H‐benzimidazol‐2‐ yl)‐N,N‐dimethylbenzenamine (N‐DMBI) as the dopant. Ultimately, the polymer with CN substituents delivered the best thermoelectric performance with a power factor of up to 2.14 μW·m−1·K−2, because it possessed the lowest LUMO energy level among the three CPs. This work highlights that the modulation of LUMO energy level is an effective strategy to optimize the thermoelectric performance of CPs.

Nucleophilic Addition of 4,5-Dihydrooxazole Derivatives to Base Generated o-Quinone Methides: A Four-Component Reaction.

A novel method for joining four components together in a single pot leading to an assortment of N-amino-benzylated phenols is described. The method involves the addition of different Grignard reagents to various o-OBoc salicylaldehydes in the presence of assorted 4,5-dihydrooxazoles, followed by aqueous workup. Seventeen examples are presented with varied (-R, -R' -R″, -R‴, -R⁗, and Cn) substituents.

A multiscale ONIOM study of the buckminsterfullerene (C60) Diels–Alder reaction: from model design to reaction path analysis

The hybrid ONIOM(Ourown N-layered Integrated molecular Orbital and molecular Mechanics) formalism is employed to investigate the Diels-Alder reaction of the buckminsterfullerene C60. Our computations suggest that the ONIOM2(M06-2X/6-31G(d): SVWN/STO-3G) model, enclosing both the diene and the pyracyclene fragment of C60 in the higher-layer, provides a reasonable trade-off between accuracy and computational cost as it comes to predicting reaction energetics. Moreover, the frontier molecular orbital (FMO) theory and activation strain model (ASM) are jointly relied on to rationalize the effect of -OH and -CN substituents on the activation barrier of this reaction. Finally, reaction paths are scrutinized to get insight into the various forces underpinning the process of cycloadduct formation.

Discovery of (E)-3-(3-((2-Cyano-4′-dimethylaminobiphenyl-4-ylmethyl)cyclohexanecarbonylamino)-5-fluorophenyl)acrylic Acid Methyl Ester, an Intestine-Specific, FXR Partial Agonist for the Treatment of Nonalcoholic Steatohepatitis

A series of fexaramine analogs were synthesized and evaluated to develop an intestine-selective/specific FXR partial agonist. Introduction of both a CN substituent at the C-2 in the biphenyl ring and a fluorine at the C-5 in the aniline ring in fexaramine markedly increased FXR agonistic activity. 27c showed 53 ± 3% maximum efficacy relative to GW4064 in an FXR agonist assay. A substantial amount of 27c was absorbed in the intestine after oral administration in rats, and then it was rapidly metabolized to inactive carboxylic acid 44 by serum esterases. In CDAHFD-fed mice, oral administration of 27c strongly induced multiple intestinal FXR target genes, FGF15, SHP, IBABP, and OST-α, but failed to activate SHP in the liver. 27c significantly reduced the liver fibrogenesis area, hepatic fibrosis markers, and serum level of AST. Rational optimization of fexaramine has led to the identification of an intestine-specific FXR partial agonist 27c.

Electronic transitions in noncovalent BODIPY dimers: TD-DFT study

Theoretical computations have been performed on the absorption spectra of (8-R-TMB)2 dimers with varying character of substituents at the 8 position (meso) at monomers units (R = NH2, OH, CH3, H, COH, CF3, CN). The obtained results (TD-CAM-B3LYP) show that the first four lower transitions of studied dimers (S0 → Si, i = 1–4) are intrinsically linked with delocalized HOMO and LUMO orbitals of the two monomers, which constitute a dimer. For all the dimers, S0 → S1 and S0 → S3 transitions are strongly forbidden, whereas S0 → S2 and S0 → S4 are allowed. There is a good agreement between the TD-CAM-B3LYP theory and the simple model of exciton coupling for two identical chromophores with the planes of two moieties, which are stacked upon each other. Intensities of the allowed transitions depend strongly on the nature of the substituent at the meso position. For the dimers with monomer units bearing electron-donor groups, S0 → S2 transitions are more intense compared with S0 → S4 ones. As the donor properties of the meso substituents diminish and electron acceptor properties enlarge, the intensity of these transitions becomes lower, whereas that of S0 → S4 transitions becomes higher. For the dimers with NH2 and CN substituents, the almost inverse ratio of intensities of the transitions discussed is observed (for example, f = 0.80 and 0.06 (in the case of NH2) and f = 0.09 and 0.72 (CN) for S0 → S2 and S0 → S4, respectively). Protonation of the tertiary amine function drastically ‘switches off’ its electron-donating properties. As a result, the red shift of the bands and redistribution of intensities of the allowed S0 → S2 and S0 → S4 transitions is predicted for protonated forms of the (8-NH2-TMB)2 dimer. This peculiarity can be of especial importance for the design of dimers with a sensor function.

Multiple established forms of palladium acetate binding to the four N-atom donor 2,3-dicyano-5,6-di(2-pyridyl)-pyrazine, [(CN)2dpp

The reaction of the ligand 2,3-dicyano-5,6-di(2-pyridyl)-pyrazine, [(CN)2dpp], with Pd(OAc)2, in CH3CN leads to the formation of three novel complexes which were characterized by thermogravimetric analysis, single crystal and powder X-ray measurements, MALDI-TOF mass spectra, IR and UV–visible spectroscopy as well as electrochemistry. As established by crystallographic work, the complex of formula [(CN)2dppPd(OAc)2]⋅H2O (molar ratio ligand/Pd(II) 1:1; species 3) shows a single Pd(OAc)2 unit coordinated to each nitrogen of the two pyridyl (py) groups of [(CN)2dpp]. i.e. the “py-py” mode of coordination previously established for the analogs [(CN)2dppMCl2] (M = Pd(II), Pt(II)). The second isolated species is a highly insoluble dinuclear Pd(II) complex of formula [(CN)2dpp{Pd(OAc)2}2]⋅5H2O (molar ratio ligand/Pd(II) 1:2; species 1), where the two Pd(OAc)2 units are each coordinated to one pyrazine nitrogen and one N atom of a pyridyl group on [(CN)2dpp] (“py-pyz” binding). Based on crystallographic work, the third isolated species is assigned the formula [(CN)(CONH)dppPd(OAc)] (molar ratio ligand/Pd(II) 1:1; species 2), which is formed by hydrolysis of a CN substituent on [(CN)2dpp] giving a –CONH- group and characterized by a “py-pyz” type of coordination. Electrochemical and spectroelectrochemical data of complexes 1, 2, and 3 in DMF and DMSO were used to assign the sites of electron transfer.

Theoretical Design of Blue-Color Phosphorescent Complexes for Organic Light-Emitting Diodes: Emission Intensities and Nonradiative Transition Rate Constants in Ir(ppy)2(acac) Derivatives.

Theoretical calculations of phosphorescent spectra and nonradiative transition (NRT) rate constants for S1 ⇝ T1, T1 ⇝ S0, and S1 ⇝ S0 were carried out to determine the best candidate for a blue-color phosphorescent complex among several derivatives of bis(2-phenylpyridine)(acetylacetonate)iridium(III). The geometries of the ground state (S0), the lowest triplet state (T1), and the lowest excited singlet state (S1) were optimized at the levels of density functional theory, in which B3LYP functionals and SBKJC+p basis sets were used. The NRT rate constants were derived by using a generating function method within the displaced harmonic oscillator model. The results of the calculation for phosphorescence showed that the introduction of F and/or CN substituents at the 4'/6'-th and 5'-th sites in 2-phenylpyridinate (ppy) ligands, respectively, causes a blue shift of the emission spectra. They also suggest that Ir(5-CN,6-F-ppy)2(acac), denoted 3(56) in the text, is a good candidate for a blue-color phosphorescent complex because a blue shift of emission spectra and a moderate intensity are obtained for phosphorescence and, furthermore, this complex is calculated to have a large rate constant for S1 ⇝ T1 and relatively smaller rate constants for T1 ⇝ S0 and S1 ⇝ S0 based on the calculations of spin-orbit coupling and nonadiabatic coupling constants.

Chromofluorogenic naphthoquinolinedione-based probes for sensitive detection and removal of Hg2+ in aqueous solutions

Mercury ions are an industrial and environmental toxin that need to be monitored and regulated in aqueous samples. We prepared six probes (1–6) using a naphthoquinolinedione ring as a fluorophore platform that contains different substituents on the quinolone ring. All probes showed abilities to selectively bind Hg2+, but their sensitivity to the detection of this metal ion significantly varied depending on the substituent pattern. Among these probes, probe 5 with Br and CN substituents on the quinolone ring was most effective for the sensitive detection of Hg2+ in aqueous solutions. This probe showed a naked-eye color change from yellow to purple upon binding to Hg2+. A ratio-metric method using UV–visible absorption data gave a limit of detection (LOD) of 20 nM, while the fluorescence-based result yielded an LOD of 0.047 pM. When bio-samples such as human urine and serum were used as media, the fluorescence-based LOD of this probe for Hg2+ detection increased to 50 nM. Probe 5 was also effective at detecting methylmercury, an organic mercury species, dissolved in drainage water or urine. Based on the results of DLS, FE-SEM, and DFT calculations, the probe appeared to form large aggregates and undergo photo-induced electron transfer (PET) upon Hg2+ binding, both of which are responsible for the probe fluorescence quenching. Probe 5 also showed the ability to sense Hg2+ within three different types of human cells: Brain cells (U87MG), Hela cells and skin cancer cells (SK-MEL28). Furthermore, this probe holds significant potential for on-site applications since various solid supports such as silica gel, filter papers and TLC plates were effectively used for sensitive and selective Hg2+ sensing, following probe coating/adsorption.

Theoretical investigation of substituent effects on the relative stabilities and electronic structure of [BnXn]2- clusters.

In this study, we provide a theoretical evaluation of relative stabilities and electronic structure for [BnXn]2- clusters (n = 10, 12, 13, 14, 15, 16). Structural and electronic characteristics of [BnXn]2- clusters are examined by comparison with the [B12X12]2- counterparts with a focus on the substituent effects (X = H, F, Cl, Br, CN, BO, OH, NH2) on the electronic structure, electron detachment energies, formation enthalpies, and charge distributions. For the electronic structure and electron detachment energies, substituent effects on boron clusters are shown to follow a very similar trend to the mesomeric and inductive effects (± M and ± I) of π-conjugated systems, and the most stable derivatives in terms of HOMO/LUMO and electron detachment energies are calculated for CN and BO substituents due to strong -M effects. In the case of formation enthalpies for larger boron clusters (n ≥ 13), the icosahedral barrier is shown to increase with the halogen and CN substitution, whereas it is possible to reduce the icosahedral barrier for the cases of X = OH and NH2. It is shown that this reduction results from destabilizing the [B12X12]2- cluster with electronic (+ M) and symmetry effects induced by OH and NH2 ligands.

Ethanol(nitrato)[tris-(4-cyano-3-phenyl-1H-pyrazol-1-yl)hydroborato]nickel(II).

The synthesis and structure is reported of TpPh,4CNNi(NO3)(EtOH) or [Ni(C30H19BN9)(NO3)(C2H6O)], the first half-sandwich complex of a cyano-scorpionate ligand. The pseudo-octa-hedral coordination sphere of the NiII ion is comprised of a tridentate tris-(4-cyano-3-phenyl-pyrazol-yl)borate ligand, a bidentate nitrate ligand and a neutral ethanol ligand. The phenyl substituents on the TpPh,4CN ligand are relatively parallel to the planes of the ethanol and nitrate ligands. An inter-molecular hydrogen-bonding inter-action is evident between the ethanol OH group and the pyrazole CN substituent. The ethanol ligand was modeled with a 0.572 (13)/0.428 (13) disorder of the methyl C atom.

CN engineered electron transport type hosts for high efficiency and extended lifetime in blue thermally activated delayed fluorescent organic light-emitting diodes

The 4DBF-BNCZ and 4DBF-PCZ with CN substituent are developed as the electron transport and high triplet energy hosts for blue TADF application. The 4DBF-BNCZ demonstrates a high EQE of 20% and device lifetime of 32.2 h up to 80%.

Efficient structural modification of electron‐withdrawing substituents on Pt(II) complexes for red emitters: A theoretical study

In this study, the electronic structures and optical properties of a cyclometalated Pt(II) complex (M1) and a series of derivatives (M1–F, M1–CF3, and M1–CN) with electron‐withdrawing substituents (–F, –CF3, and –CN) at the carbazole moiety were theoretically investigated by density functional theory and time‐dependent density functional theory. The calculation results reveal that these Pt complexes display deep red phosphorescence emission above Λ = 640 nm. When the 3MLCT/π → π* to triplet metal‐centered 3MC/d–d state decay mechanism is taken into consideration, the nonradiative decay rate constant (knr) decreased in the order M1 > M1–CF3 > M1–F > M1–CN. The <T1|HSOC|Sm> and kr values of M1‐F are similar with those of M1, however the Knr rate ofM1‐F is larger than that of M1. M1–F is expected to have improved quantum yields. Moreover, through the analyses of the HOMO/LUMO level and triplet energy, it is found that the introduction of –F and –CN substituents in M1 results in efficient energy transfer from the host material 4,4′‐N,N′‐dicarbazole‐biphenyl to these complexes. In view of the electroluminescent applications in organic light‐emitting diodes, M1–F can serve as efficient deep‐red guest materials with improved electron injection and transport ability.