Intramolecular Donor-acceptor Interactions Research Articles

Extended Conjugation Strategy Enabling Red-Shifted and Efficient Emission of Orange-Red Thermally Activated Delayed Fluorescence Materials.

In account of the energy gap law, the development of efficient narrow-band gap thermally activated delayed fluorescence (TADF) materials remains a major challenge for the application of organic light-emitting diodes (OLEDs). The orange-red TADF materials are commonly designed with either large π-conjugated systems or strong intramolecular donor-acceptor (D-A) interactions for red-shift emission and small singlet-triplet energy gap (ΔEST). There are rare reports on the simultaneous incorporation of these two strategies on the same material systems. Herein, two orange-red emitters named 1P2D-BP and 2P2D-DQ have been designed by extending the conjugation degree of the center acceptor DQ and increasing the number distribution of the peripheral donor PXZ units, respectively. The emission peak of 1P2D-BP is red-shifted to 615 nm compared to 580 nm for 2P2D-DQ, revealing the pronounced effect of the conjugation extension on the emission band gap. In addition, the distorted molecular structure yields a small ΔEST of 0.02 eV, favoring the acquisition of a high exciton utilization through an efficient reverse intersystem crossing process. As a result, orange-red OLEDs with both 1P2D-BP and 2P2D-DQ have achieved an external quantum efficiency (EQE) of more than 17%. In addition, the efficient white OLED based on 1P2D-BP is realized through precise exciton assignment and energy transport modulation, showing an EQE of 23.6% and a color rendering index of 82. The present work provides an important reference for the design of high-efficiency narrow-band gap materials in the field of solid-state lighting.

Synthesis and Photophysical Properties of Carbazole-Functionalized Diazaphosphepines via Sequent P-N Chemistry.

Chemical structure tunability of organic π-conjugated molecules (OCMs) is highly appealing for fine-tuning the optoelectronic properties. Herein, we report a new series of carbazole-functionalized diazaphosphepines (DPP-CBZs) via one-pot phosphorus-nitrogen (P-N) chemistry. The one-pot synthesis harnessed the mild and selective P-N chemistry that successively installed carbazole moieties and seven-membered heterocycles at one P-center. Single-crystal structure studies revealed the tweezer-like structures for 1PO, 2PO, and 3PO that maintained the intramolecular donor-acceptor interactions between [d]-aryl moieties and carbazole. DPP-CBZs exhibited a more twisted central-diazaphosphepine ring compared with the reference molecules (1-3MO without carbazole group). DPP-CBZs with strong electron-accepting [d]-Ars generally showed lower photoluminescence quantum yields (PLQYs) than those of the reference molecules, which is probably due to the intramolecular charge transfer (ICT) from electron-donating carbazole to electron-withdrawing [d]-Ars. Upon the oxidation of the P-centers, PLQYs of DPP-CBZs increased. Furthermore, photophysical studies and theoretical studies suggested that the carbazole group had a strong impact on the structures of DPP-CBZs. As a proof of concept, we showed that grinding the mixture of 1PO as the electron-donating tweezer and benzene-1,2,4,5-tetracarbonitrile (BzCN) as the electron acceptor induced the formation of the CT complex.

Dicyanovinyl-capped thiazologermoles with moderate donor-acceptor interaction as visible photoluminescence turn-on sensors for primary amines

Dicyanovinyl-capped thiazologermoles (DTzG-DCV and GIDTz-DCV) were synthesized, and their optical and electrochemical properties were investigated. Both DTzG-DCV and GIDTz-DCV showed solvatochromism, exhibiting red shifts of the photoluminescence (PL) bands with increasing solvent polarity from toluene to DMF, likely due to intramolecular donor–acceptor interaction. Moreover, they served as selective PL sensors, with spectral changes in the presence of amines and fluoride and iodide ions, but not other halogen ions, in solution. DTzG-DCV and GIDTz-DCV underwent a quick and high-yield reaction with n-butylamine to give imine derivatives, accompanied by PL color changes. Similar color changes were observed even in the solid state with n-butylamine and n-hexylamine. In contrast, reactions with secondary and tertiary alkylamines caused no obvious changes in PL color. The color changes are visible to the naked eye under irradiation with a portable UV lamp at 365 nm, and thus DTzG-DCV and GIDTz-DCV can be used for the quick and selective sensing of primary amines.

Tuning Local Charge Distribution in Multicomponent Covalent Organic Frameworks for Dramatically Enhanced Photocatalytic Uranium Extraction.

Optimizing the electronic structure of covalent organic framework (COF) photocatalysts is essential for maximizing photocatalytic activity. Herein, we report an isoreticular family of multivariate COFs containing chromenoquinoline rings in the COF structure and electron-donating or withdrawing groups in the pores. Intramolecular donor-acceptor (D-A) interactions in the COFs allowed tuning of local charge distributions and charge carrier separation under visible light irradiation, resulting in enhanced photocatalytic performance. By optimizing the optoelectronic properties of the COFs, a photocatalytic uranium extraction efficiency of 8.02 mg/g/day was achieved using a nitro-functionalized multicomponent COF in natural seawater, exceeding the performance of all COFs reported to date. Results demonstrate an effective design strategy towards high-activity COF photocatalysts with intramolecular D-A structures not easily accessible using traditional synthetic approaches.

Efficient Narrowband Circularly Polarized Light Emitters Based on 1,4-B,N-embedded Rigid Donor-Acceptor Helicenes.

Narrow-band emission is essential for applicable circularly polarized luminescence (CPL) active materials in ultrahigh-definition CP-OLEDs. One of the most promising classes of CPL active molecules, helicenes, however, typically exhibit broad emission with a large Stokes shift. We present, herein, a design strategy capitalizing on intramolecular donor-acceptor interactions between nitrogen and boron atoms to address this issue. 1,4-B,N-embedded configurationally stable single- and double helicenes were synthesized straightforwardly. Both helicenes show unprecedentedly narrow fluorescence and CPL bands (full width at half maximum between 17-28 nm, 0.07-0.13 eV) along with high fluorescence quantum yields (72-85 %). Quantum chemical calculations revealed that the relative localization of the natural transition orbitals, mainly on the rigid core of the molecule, and small values of root-mean-square displacements between S0 and S1 state geometries, contribute to the narrower emission.

Synthesis of Push-Pull Azulene-Based Compounds

Nowadays, non-benzenoid aromatic hydrocarbons are widely used as synthons for the production of new organic semiconductors with interesting photophysical characteristics. For instance, a non-benzoid azulene hydrocarbon with a polar structure, a narrow energy gap between the highest free and lowest occupied molecular orbital and the ability to form stable ions can be intended as a structural moiety for the synthesis of new conjugated compounds with important optical and electronic properties. The article discusses the synthesis and investigation of the optical properties of new push-pull azulene-based compounds. It shows that Friedel-Crafts acylation is used as the key reaction for the synthesis of methyl- and phenyl-dicyanovinylated azulenes. The interaction proceeds regioselectively at the C1 and C3 positions of the five-membered azulene ring. It is identified that the synthesis of push-pull dicyanovinylated azulenes by Knoevenagel condensation of azulenyl ketones with malononitrile proceeds easily in Py and DMSO. The UF-vis spectra of the obtained azulene push-pull compounds demonstrated strong electron absorption in the visible zone with λmax at 410, 430, 434 and 452 nm associated with transport of charge between the donor azulene ring and the acceptor dicyanovinyl group. The scheme of resonant structures shows the mechanism of intramolecular donoracceptor interaction. The structure of the synthesized push-pull dicyanovinylated nonazulenes was elucidated using modern physicochemical and spectroscopic research methods.

Solution-Phase Synthesis and Isolation of An Aza-Triangulene and Its Cation in Crystalline Form.

Synthesis of triangulene and its derivatives is challenging due to their intrinsic high spin nature. Herein, we report solution-phase synthesis and isolation of a nitrogen-doped triangulene (i.e., aza-triangulene) (NT) and its cation (NT+ ) in single-crystal form. Notably, the cation NT+ can be regarded as an isoelectronic structure of the corresponding all-carbon triangulene. Both NT and NT+ show reasonable stability due to kinetic blocking by bulky and electron-withdrawing aryl substituents, and intramolecular donor-acceptor interaction. Bond length analysis, magnetic measurements and theoretical calculations reveal that the neutral NT has a doublet ground state with a zwitterionic character, while the cation NT+ exhibits a triplet ground state with a singlet-triplet energy gap of +0.84 kcal mol-1 . This study provides a rational strategy to access high-spin systems by heteroatom doping of pure π-conjugated polycyclic hydrocarbons.

Stable Triarylmethyl Radicals and Cobalt(II) Ions Based 1D/2D Coordination Polymers.

The incorporation of organic radicals into coordination polymers was considered as a promising strategy to promote metal-ligand exchange interactions, but there are only a very limited number of stable organic radical-based ligands that can serve well such a purpose. Herein, we report two new tris(2,4,6-trichlorophenyl)methyl (TTM) radical-based ligands L1 and L2 with two and three imidazole substituents, respectively. The imidazole unit serves as a coordination site and it can also stabilize the TTM radical by intramolecular donor-acceptor interaction. Coordination of L1 and L2 with cobalt(II) ions gave the corresponding one- (CoCP-1) and two-dimensional (CoCP-2) coordination polymers, the structures of which were confirmed by X-ray crystallographic analysis. Magnetic measurements and theoretical calculations suggest antiferromagnetic coupling between the paramagnetic cobalt(II) ions and the radical ligands. Our study provides a rational design for stable organic radical-based ligands and further demonstrated the feasibility of a metal-radical approach toward magnetic materials.

Interrupted intramolecular donor-acceptor interaction compensated by strong through-space electronic coupling for highly efficient near-infrared TADF with emission over 800 nm

Near-infrared (NIR) organic emitters with emission wavelength from 700 to 900 nm show promising application in phototherapy, bioimaging and night vision products. The traditional fluorescent compounds composed of strong donor (D) and acceptor (A) units can readily achieve NIR emission via the extensive conjugation over the molecular skeleton. However, the development of NIR thermally activated delayed fluorescence (TADF) is still an unaddressed issue mainly due to the limited conjugation between D and A within TADF molecules. Here, the strategy is to introduce strong D/A fragments into the molecular skeleton and to incorporate the strong through-space electronic coupling between TADF molecules simultaneously. With this strategy, we demonstrate an unprecedented NIR TADF material (AQTC-DTPA) with emission over 800 nm. TADF OLEDs based on AQTC-DTPA show the record-high maximum External quantum efficiencies (EQE) of 0.51%/0.41%/0.30%/0.23% with Electroluminescence (EL) peak wavelength at 810/828/852/894 nm, respectively.

Hydroboration of alkynylchlorosilanes as an efficient route for the synthesis of SiNNB heterocycles

AbstractAlkenylsilanes bearing chlorosilyl and boryl groups geminally attached to a carbon atom ((E)‐3‐(9‐borabicyclo[3.3.1]nonan‐9‐yl)‐N,N‐dimethyl‐3‐(trichlorosilyl)prop‐2‐en‐1‐amine, 1, (1‐(9‐borabicyclo[3.3.1]nonan‐9‐yl)‐3,3‐dimethylbut‐1‐en‐1‐yl)dichloro (phenyl)silane, 2, (1‐(9‐borabicyclo[3.3.1]nonan‐9‐yl)‐2‐phenylvinyl) chloro (methyl)(phenyl)silane, 3, (1‐(9‐borabicyclo[3.3.1]nonan‐9‐yl)hex‐1‐en‐1‐yl)trichlorosilane, 4) are accessible by hydroboration of the corresponding alkynylsilanes. Only the vinyl group of 1 adopted E configuration, which may be favored by ring closure via an intramolecular B–N bonding interaction. Compounds 2–4 reacted with N‐trimethylsilylpyrazole and N‐2‐(trimethylsilylamino)pyridine by elimination of ClSiMe3 and formation of Si–N bonds. Intramolecular donor–acceptor interactions between the N and B atoms afforded five‐ and six‐membered heterocycles, which contained Si, N, and B as heteroatoms. A bis(pyrazolyl)silane was isolated upon treatment of a dichlorosilane with two equivalents of trimethylsilylpyrazole.

Ditopic Phosphide Oxide Group: A Rigidifying Lewis Base to Switch Luminescence and Reactivity of a Disilver Complex.

Heterodentate phosphines containing anionic organophosphorus groups remain virtually unexplored ligands in the coordination chemistry of coinage metals. A hybrid phosphine-phosphine oxide (o-Ph2PC6H4)2P(O)H (HP3O) readily forms the disilver complex [Ag2(P3O)2] (1) upon deprotonation of the (O)P-H fragment. Due to the electron-rich nature, the anionic phosphide oxide unit in 1 takes part in efficient intermolecular hydrogen bonding, which has an unusual and remarkably strong impact on the photoluminescence of 1, changing the emission from red (644 nm) to green-yellow (539 nm) in the solid. The basicity of the R2(O)P- group and its affinity for both inter- and intramolecular donor-acceptor interactions allow converting 1 into hydrohalogenated (2, 3) and boronated (4) derivatives, which reveal a gradual hypsochromic shift of luminescence, reaching the wavelength of 489 nm. Systematic variable-temperature analysis of the excited state properties suggests that thermally activated delayed fluorescence is involved in the emission process. The long-lived excited states for 1-4, the energy of which is largely regulated by means of the phosphide oxide unit, are potentially suitable for triplet energy transfer photocatalysis. With the highest T1 energy among 1-4, complex 4 demonstrates excellent photocatalytic activity in a [2+2] cycloaddition reaction, which has been realized for the first time for silver(I) compounds.

Isolation and Structural Determination of a Hexacoordinated Antimony(V) Dication.

Invited for the cover of this issue are Masato Sakabe and Soichi Sato at Tokyo Metropolitan University. The image depicts the new hexacoordinated dicationic antimony species reported in this work. Read the full text of the article at 10.1002/chem.202004659.

Mixed ligand copper(II) chelates derived from an O, N, S- donor tridentate thiosemicarbazone: Synthesis, spectral aspects, FMO, and NBO analysis

Five new copper(II) chelates [(Cu(bmct))2] (1), [Cu(bmct)(phen)] (2), [Cu(bmct)(bipy)] (3), [Cu(bmct)(4,4′-dmbipy)] (4) and [Cu(bmct)(5,5′-dmbipy)] (5) with 5-bromo-3-methoxysalicylaldehyde-N(4)-cyclohexylthiosemicarbazone (H2bmct) as the chelating ligand and 1,10-phenanthroline, 2,2′-bipyridine, 4,4′-dimethylbipyridine, 5,5′-dimethylbipyridine as coligands have been synthesized and characterized by different physicochemical techniques like CHNS analysis, molar conductivity and magnetic studies, IR, UV/Vis and EPR spectral studies. In all the complexes, the thiosemicarbazone exists in thioiminolate form and coordinates to the metal through azomethine nitrogen, thioiminolate sulfur, and phenolate oxygen. EPR spectra in polycrystalline state at 298 K showed that compounds 1, 4, and 5 are isotropic, 2 is axial and 3 is rhombic in nature. In DMF at 77 K, compound 1 showed hyperfine lines in the parallel and perpendicular regions as well as superhyperfine lines due to the interaction of copper center with azomethine nitrogen of the ligand. Complex 2, in which g||>g⊥> 2.0023 suggests a distorted square pyramidal structure. To analyze the stability of the complexes, quantum chemical parameters like hardness, softness, polarizability, electrophilicity, electronegativity, and dipole moment were calculated and discussed within the framework of electronic structure principles known as Maximum Hardness, Minimum Polarizability and Minimum Electrophilicity Principles. Besides, the intramolecular donor–acceptor interactions for all complexes were evaluated by using NBO analysis. All calculations proved that Compound 3 is the most stable chelate among them.

Suppression of Concentration Quenching in Ortho‐Substituted Thermally Activated Delayed Fluorescence Emitters

AbstractThermally activated delayed fluorescence (TADF) emitters are typically embedded at low concentrations in a host matrix to suppress emission quenching. However, recent studies indicate that TADF compounds such as the oBFCzTrz emitter (5‐(2‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐5H‐benzofuro[3,2‐c]carbazole) display insignificant concentration quenching dependence. To understand the origin of this beneficial behavior, the morphology, dynamics, electronic properties, and charge transport and energy transfer in a neat film of the oBFCzTrz emitter are characterized via molecular dynamic simulations combined with density functional theory calculations. The emissive layer shows glassy behavior at room temperature with the twisted configurations of the emitter molecules allowing for intramolecular donor–acceptor interactions, but disfavoring intermolecular π–π stacking, which suppresses the formation of intermolecular aggregate states. As a result, the electronic structure and luminescence of oBFCzTrz are not significantly altered by intermolecular interactions. The calculated diffusion lengths of the singlet and triplet excitons are small enough that there occurs no substantial concentration quenching effect. Overall, the design of new TADF emitters with structural motifs similar to those of oBFCzTrz offers potential to develop efficient organic light‐emitting diode devices in which the emissive layers are entirely composed of TADF molecules without the need for a host component.

Vibrational spectroscopic investigation and DFT computation of nonlinear optical crystal L-Glutaminium 4-methylbenzenesulfonate

A nonlinear organic crystal, L-Glutaminium 4-methylbenzenesulfonate was synthesized by slow evaporation crystal growth technique. Theoretical as well as experimental FT-IR, FT-Raman and UV–vis spectra were analyzed and the formation of crystal was confirmed using powder X-ray diffraction study. The existence of intramolecular donor-acceptor interactions through N–H⋯O hydrogen bonds were confirmed with vibrational spectroscopic and natural bond orbital methods. The photoluminescence spectrum was recorded and analyzed. Kurtz and Perry powder technique was employed to detect the second harmonic generation of the grown crystal. Moreover, molecular electrostatic potential and Mullikan charge distribution were studied for identifying the most reactive sites of the compound.

Triindolo-Truxene Derivatives: Design, Synthesis, and Fine-Tuning of Electronic Properties and Molecular Assembly through Molecular Engineering.

Triindolo-truxene, a C3 -symmetric molecule with a large π-conjugated plane, has six methylene carbon atoms and three aromatic carbon atoms that can be facilely functionalized. Herein, butyl, carbonyl, cyano, and/or malononitrile groups were introduced at six methylene carbon atoms (6-, 14-, 22- or 8-, 16-, 24-positions) and/or three aromatic carbon atoms (2-, 10-, and 18-positions) of triindolo-truxene to produce eight derivatives. Their photophysical properties, electrochemical properties, and molecular assembly can be effectively modulated by substituents and substitution patterns. Incorporation of electron-deficient groups led to redshifts in both the absorption and emission of these derivatives and also lowered their HOMO and LUMO levels. Different substitution patterns resulted in the different intramolecular donor-acceptor interactions. Electron-deficient substituents at the methylene carbon atoms in the 6-, 14-, and 22-positions led to intramolecular charge transfer from the fluorene arms to the truxene core, whereas the corresponding substitutions at the methylene carbon atoms in the 8-, 16-, and 24-positions resulted in intramolecular charge transfer from the truxene core to the fluorene arms. The molecular packing in single crystals and molecular aggregation in solution are also influenced by the substituents and substitution patterns. This work provides a straightforward strategy to alter the properties of triindolo-truxene.

Synthesis and properties of new carbazole-containing metallopolymers with transannular polyconjugation in the backbone

New metal-containing polymers, poly(salicylidene azomethines) containing metal atoms (Co, Ni, Cu) in the backbone, were synthesized from aromatic carbazolediamine derivatives. It was found that the polymers with a decyl substituent in the carbazole fragment are soluble in organic solvents (chloroform, methanol, DMSO, DMF) and exhibit film-forming and semiconductor properties. IR and NMR spectroscopy was used to show that the semiconductor properties of the new polymers are associated with the presence in the polymer backbone of transannular polyconjugation zones formed by intramolecular donor‒acceptor interactions of the metal and nitrogen valence shells.

Spectroscopic and DFT-based computational studies on the molecular electronic structural characteristics and the third-order nonlinear property of an organic NLO crystal: (E)-N′-(4-chlorobenzylidene)-4-methylbenzenesulfonohydrazide

Single crystals of (E)-N′-(4-chlorobenzylidene)-4-methylbenzenesulfonohydrazide (CBMBSH) have been grown by slow evaporation crystal growth method. The structure stabilizing intramolecular donor-acceptor interactions and the presence of the NH⋯O, CH⋯O and CH⋯C(π) hydrogen bonds in the crystal were confirmed by vibrational spectroscopic and DFT methods. The linear optical absorption characteristics of the solvent phase of CBMBSH were investigated using UV–Vis-NIR spectroscopic and TD-DFT approaches. The 2PA assisted RSA nonlinear absorption and the optical limiting properties of CBMBSH were studied using the open-aperture Z-scan method. The topological characteristics of the electron density have been determined using the quantum theory of atoms in molecules method.

NATURAL BOND ORBITAL ANALYSIS OF CYCLIC AND ACYCLIC “C-H” ACIDS

The high acidity of Meldrum’s acid, barbituric and tetronic acids in comparison to their acyclic analogues was explained by density functional theory and calculations and by natural bond orbital analysis. The present study shows that cyclic b-dicarbonyl compounds are remarkably stabilized by intramolecular donor-acceptor interactions and this effect is absent in their acyclic analogues.

A photon-working on/off switch for intramolecular donor-acceptor interactions and invisible modulation of the fluorescence.

An on/off switching for charge-transfer interactions between the side chains of a diarylethene based on photochromic reactions has been proved by the disappearance and appearance of an additional fluorescence band.