Effective exciplex system with high emission efficiency via intramolecular hydrogen bonding for efficient solution processable OLEDs

Exciplex system is a charming candidate for thermally activated delayed fluorescence(TADF)due to its intrinsic small energy difference between the lowest singlet state and triplet excited state(ΔEST).However,high emission efficiency and fast radiative decay rate are still a formidable task for the exciplex emission.Herein two novel tri(triazolo)triazine-based TADF emitters,named TTT-HPh-Ac and TTTMePh-Ac,are synthesized and characterized.Using such TADF emitters as the donor molecule and(1,3,5-triazine-2,4,6-triyl)tris(benzene-3,1-dial)tris(diphenylphosphine oxide)(PO-T2T)as the acceptor molecule,the exciplex system of TTT-HPh-Ac:PO-T2T and TTT-MePh-Ac:PO-T2T are prepared,which show a tinyΔEST of 40±20 meV and fast reverse intersystem crossing rate.As a result,very high emission efficiency(97%)and a small non-radiative decay rate are detected for the exciplex TADF system.The solution processable organic light-emitting diode using the exciplex system as the emitter achieves a maximum external quantum efficiency(EQE_(max))of 17.0%.When using the exciplex as the host matrix,the TTT-MePh-Ac:PO-T2T based solution processable device shows a better performance with an EQE_(max)of 20%with a very small efficiency roll-off of 6%at 1000 cd m^(−2).This work proves that the molecule with both intramolecular hydrogen bonding and proper twisted molecular geometry in exciplex is more favorable to enhance its emission efficiency and suppress the non-radiative transition,which provides a new way to develop efficient and stable exciplex emitters.

Intramolecular Hydrogen Bond Improved Durability and Kinetics for Zinc‑Organic Batteries

Organic compounds have the advantages of green sustainability and high designability,but their high solubility leads to poor durability of zinc-organic batteries.Herein,a high-performance quinone-based polymer(H-PNADBQ)material is designed by introducing an intramolecular hydrogen bonding(HB)strategy.The intramolecular HB(C=O⋯N-H)is formed in the reaction of 1,4-benzoquinone and 1,5-naphthalene diamine,which efficiently reduces the H-PNADBQ solubility and enhances its charge transfer in theory.In situ ultraviolet-visible analysis further reveals the insolubility of H-PNADBQ during the electrochemical cycles,enabling high durability at different current densities.Specifically,the H-PNADBQ electrode with high loading(10 mg cm^(-2))performs a long cycling life at 125 mA g^(-1)(>290 cycles).The H-PNADBQ also shows high rate capability(137.1 mAh g^(−1)at 25 A g^(−1))due to significantly improved kinetics inducted by intramolecular HB.This work provides an efficient approach toward insoluble organic electrode materials.

A DFT Study on Intramolecular Hydrogen Bond in Substituted Catechols and Their Radicals

Density functional theory (DFT) at B3LYP/6-31G(d,p) level was employed to calculate intramolecular hydrogen bond enthalpies (HIHB), O-H charge differences, O-H bond lengths and bond orders for various substituted catechols and their radicals generated after H-abstraction. It was found that although the charge difference between hydrogen-bonded H and O played a role in determining HIHB, HIHB was mainly governed by the hydrogen bond length. As the oxygen-centered radical has great tendency to form a chemical bond with the H atom, hydrogen bond lengths in catecholic radicals are systematically shorter than those in catechols. Hence, the HIHB for the former are higher than those for the latter.

Study on the Intramolecular Hydrogen Bonds of Dibenzofurans, Xanthones and Anthraquinones with One or Two Positions Substituted by Hydroxyls

The thermodynamic properties of dibenzofurans （DFs）, xanthones （XTs） and an-thraquinones （AQs） with one and two positions substituted with hydroxyls in the ideal gas state at 298.15 K and 1.013×10^5 pa were calculated at the B3LYP/6-311G^＊ level using Gaussian 03 program. The isodesmic reactions were designed to calculate the standard free energy of formation （△fG^θ）. Three types of hydrogen bonds exist in the three kinds of chemicals and their bond energies were ascertained as 7-15, 15-23 and 49-58 kJ·mo1^-1 respectively by comparing the △fG^θ values. Electronic density topology analysis was applied to validate the strength of bond.

A^1HNMR STUDY ON THE FORMATION AND BREAKING OF INTRAMOLECULAR HYDROGEN BONDS OF BILIRUBIN IN CDCl_3-DMSO-d_6 BINARY SOLVENT

The formation and breaking of intramolecular hydrogen bonds of bilirubin in CDCl_3-DMSO-d_6 binary solvent have been investigated by means of NMR spectroscopy.The chemical shifts of protons at dipyrrinone lactam C=O and N-H,Pyrrole N-H,C-5,C-15 and methylene groups of 8,12-propionic acid side-chains changed markedly as a function of composition of the binary solvent.The hydrogen bond formation is dependent on the conformation of propionic acid side-chains.

Intramolecular Resonance-assisted Hydrogen Bonds in N-Salicylidene-anilines

In the crystal structures of N-salicylidene-anilines, the ortho-OH group with the central N atom forms a planar six-membered ring through intramolecular hydrogen bonds (Fig. 1). The pseudo-aromatic ring is coplanar with its attached phenyl ring. The resonance strengthens the H-bond through proton transfer between the O and N atoms (Fig. 1, I II): dCO and dCC become shorter and dCN longer significantly. The d1～d6 are also changed regularly. According to the geometries obtained from X-ray analysis and retrieved from the Cambridge Structural Database (CSD, version 5.21)[1], we believe that the main resonance, at least in solid state, is the molecular keto form (II, Fig. 1) instead of the zwitterionic one (III, Fig. 1).

Structure and Vibrational Spectroscopy of 2-Methylallyl Alcohol

The intramolecular O−H…πhydrogen bond has garnered significant research interest in recent decades.In this work,we utilized the infrared(IR)-vacuum-ultraviolet(VUV)nonresonant ionization detected IR spectroscopy(NRID-IR)method to study the molecular structure of neutral and cationic 2-methylallyl alcohol(MAA,CH_(2)=C(CH_(3))−CH_(2)−OH).Density functional theory calculations revealed five stable neutral and three stable cationic MAA conformers,respectively.Two neutral MAA conformers are expected to have an O−H…πintramolecular hydrogen bond interaction,based on the structural characterization that the OH group is directed toward the C=C double bond.The IR spectra of both neutral(2700−3700 cm^(−1))and cationic MAA(2500−7200 cm^(−1))were measured,and the anharmonic IR spectra were calculated at the B3LYP-D3(BJ)/def2-TZVPP level.The OH stretching vibration frequency of neutral MAA was observed at 3656 cm−1,slightly lower than those of methanol and ethanol.In contrast,the OH stretching vibration of cationic MAA was red-shifted by about 140 cm^(−1)compared to neutral MAA.The interaction region indicator and natural bond orbital analysis suggest that the O−H…πinteraction in neutral MAA is weak,and may not play a major role in stabilizing the neutral MAA.

Effects of π-conjugation-substitution on ESIPT process for oxazoline-substituted hydroxyfluorenes

Excited-state intramolecular proton transfer(ESIPT) molecules are broadly applied to UV absorbers, fluorescence sensing, and lighting materials. In previous work, the fluorescence colors of oxazoline-substituted hydroxyfluorenes and hydroxylated benzoxazole were diversified by adding the π-conjugation. There is intriguing that the mechanism of diversified fluorescence colors induced by ESIPT. Here, the density functional theory(DFT) and time-dependent DFT(TDDFT)are advised to identify the effects of π-conjugation on ESIPT and photophysical properties. The stabilized geometrical configurations, frontier molecular orbitals(FMOs) isosurfaces, and O–H stretching vibration frequency analysis demonstrate that PT processes are more active in S1state. Constructing the minimum energy pathways of ESIPT processes, we find that the calculated peak of enol and keto fluorescence of naphthoxazole(NO–OH) is distinctly bathochromic-shift relative to the oxazoline-substituted hydroxyfluorenes(Oxa–OH) configuration when adding π-conjugation-substitution, and it means that π-conjugation-substitution can diversify the fluorescence color. We hope our studies can establish new channels to devise the ESIPT-based molecules.

Installing hydrogen bonds as a general strategy to control viscosity sensitivity of molecular rotor fluorophores Special Collection:Aggregation-Induced Processes and Functions

Molecular rotor-based fluorophores(RBFs)activate fluorescence upon increase of micro-viscosity,thus bearing a broad application promise in many fields.However,it remains a challenge to control how fluorescence of RBFs responds to viscosity changes.Herein,we demonstrate that the formation and regulation of intramolecular hydrogen bonds in the excited state of RBFs could modulate their rotational barrier,leading to a rational control of how their fluorescence can be activated by micro-viscosity.Based on this strategy,a series of RBFs were developed based on 4-hydroxybenzylidene-imidazolinone(HBI)that span a wide range of viscosity sensitivity.Combined with the AggTag method that we previously reported,the varying viscosity sensitivity and emission spectra of these probes enabled a dualcolor imaging strategy that detects both protein oligomers and aggregates during the multistep aggregation process of proteins in live cells.In summary,our work indicates that installing intracellular excited state hydrogen bonds to RBFs allows for a rational control of rotational barrier,thus allow for a fine tune of their viscosity sensitivity.Beyond RBFs,we envision similar strategies can be applied to control the fluorogenic behavior of a large group of fluorophores whose emission is dependent on excited state rotational motion,including aggregation-induced emission fluorophores.

Raman and Infrared Spectra for All-trans-astaxanthin in Dimethyl Sulfoxide Solvent

The Raman and infrared spectra of all-trans-astaxanthin （AXT） in dimethyl sulfoxide （DMSO） solvent were investigated experimentally and theoretically. Density functional cal-culations of the Raman spectra predict the splitting of the υ1 band into υ1-1 and υ1-2 compo-nents. The absence of splitting in Raman experimental spectra is ascribed to the competition between the two symmetric C=C stretching vibrations of the backbone chain. The υ1 band is very sensitive to the excitation wavelength： resonance excitation stimulates the higher-frequency υ1-2 mode, and off-resonance excitation corresponds to the lower-frequency υ1-1 mode. Analyses of the intramolecular hydrogen bonding between C=O and O-H in the AXT/DMSO system reveal that the C4=O1...H1-O3 and C4＇=O2...H2-O4 bonds are strengthened and weakened, respectively, in the electronically excited state compared with those in the ground state. This result reveals significant variations of the AXT molecular structure in different electronic states.

Thermal decomposition behaviour of polyacrylamidomethyltrimethyl ammonium chloride in red mud separation process

In order to provide references for selecting highly efficient red mud flocculants, the behaviour of polyacrylamidomethyltrimethyl ammonium chloride （PATAC） in red mud separation process was investigated. PATAC was employed as a flocculant for red mud separation from the caustic aluminate liquor at 95 ℃. The used red mud was generated from Chinese diaspore bauxite in Bayer process of alumina production. And the changes of PATAC before or after being treated in caustic solution at 95 ℃ were studied by thermogravimetry （TG） and Fourier transform infrared （FTIR） spectral analysis. The results show that PATAC fails in effectively focculating red mud and PATAC is readily converted to a quaternary ammonium hydroxide （PATAH） in caustic solution. PATAH can be decomposed to a new polymer （HPATAH） even at 95 ℃. Furthermore, there is an intramolecular hydrogen bond formed in the HPATAH polymer chain with two functional groups of--CH2--OH and --CONH2. Therefore, the poor flocculation property of PATAC for red mud separation can be attributed to the thermal decomposition of PATAC in the caustic red mud slurry at 95 ℃ and the formation of intramolecular hydrogen bond in the polymer chain of HPATAH during the thermal decomposition, which causes the absorbable functional groups of PATAC to decrease greatly.

A New Condensation Reaction of β-Keto-δ-valerolactone with Substituted Aniline

A new condensation reaction of β-keto-δ-valerolactones was developed. The condensation products are composed of a pair of isomers because of the formation ofintramolecular hydrogen bond. Their structures were confirmed by 1HNMR and elemental analysis.

Density Functional Theoretical Studies on Effect of Intramolecular Hydrogen Bonds on Reduction of Nitrophenols

Intramolecular hydrogen bonds（IMHBs） can lead to different physicochemical characteristics of nitro- phenols（NPs） that determine their environmental behavior. In the present work, to reveal the relationship between IMHB and nitrophenol reduction, the effects of IMHB on the molecular geometries and properties of a series of ni- trophenols were investigated with density functional theory（DFT） calculations. The results of the geometry optimiza- tion and atoms-in-molecules（AIM） analysis indicate relatively strong IMHBs in ortho-substituted nitrophenols, whose stability could be significantly improved. In comparing the ELUMO and adiabatic electron affinities（AEA） of the nitrophenol isomers, the presence of IMHBs benefited the reductive degradation of NPs, consistent with a previous study. To gain an insight into the effect mechanism of IMHBs on the reductive degradation behavior of these mole- cules, the condensed electrophilicity Fukui index（f-）, natural charges and Wiberg bond orders of these nitrophenol isomers were calculated. The calculations indicate that the electrophilic reactivity activity of the O atom on the nitro group could be significantly improved due to the formation of IMHBs, which results in the enhanced reductive degradation of ortho-substituted NPs.

Synthesis and Theoretical Study of Intramolecular Hydrogen Bond at Two Possible Positions in Pyrazolo[1,2-b]phthalazine

Properties of dimethyl 3-（alkylamino）-5,10-dioxo-5,10-dihydro-1H-pyraolo[1,20b]phthalazine-1,2-dicarboxy-late and its derivatives were studied by means of ab initio method. NO2 derivative of title compound was synthe- sized and the nature of its intramolecular hydrogen bond （HB） was investigated. Furthermore, the topological prop- erties of the electron density distributions for N--H＇＂O intramolecular bridges were analyzed in terms of the Bader theory of atoms in molecules （AIM）. The electron density （p） and Laplacian （V2p） properties, estimated by AIM calculations, indicated that O＇--H bond possesses low P and positive VZp values which are in agreement with elec- trostatic character of the HBs, whereas N--H bonds have covalent character （V2p〈0）. Moreover, steric effect of the t-Bu group on structure and topological parameters of pyrazolo[1,2-b]phthalazine conformers was studied. Fi- nally, the powerful method of Espinosa was used to obtain the H-bond energy.

ESIPT-regulated Mechanoresponsive Luminescence Process by Introducing Intramolecular Hydrogen Bond in Naphthalimide Derivatives

Herein,two compounds,4-2′-hydroxybenzylidenehydrazinyl-N-butyl-1,8-naphthalimide(BN-1)and 4-benzylidenehydrazinyl-N-butyl-1,8-naphthalimide(BN-2),were synthesized to explore the hydrogen bonding effect on mechanoresponsive luminescent(MRL).The results showed that compound BN-1 exhibited strong emission in solution and solid-state compared with compound BN-2.After grinding,the emission intensity of compound BN-1 sharply decreased by as much as 15 times with an obvious red-shift from 552 nm to 577 nm.The control compound BN-2,by contrast,did not change so much before and after grinding.Single crystal analysis suggests that BN-1 molecule formed strong intramolecular interaction via-N=N⋯H-O hydrogen bond with a distance of 0.2632 nm.An excited-state intramolecular proton transfer(ESIPT)based fluorophore featured this intramolecular hydrogen bond.The intramolecular hydrogen bond as well as other intermolecular interactions can rigidify the molecular conformation of compound BN-1 in solid-state,and thus suppress the nonradiative pathways,resulting in strong emission.These intra-and intermolecular interactions were destroyed by mechanical stimuli,accompanied by molecular conformation change that decreases the luminescence and blocks the ESIPT process.The MRL process was also demonstrated by scanning electron microscopy and powder X-ray diffraction.The molecular stacking mode changed from crystalline to a disordered amorphous state after grinding.

Synthesis and Structural Characterization of N,N-disubstituted Acylguanidines

A series of five N,N-disubstituted acylguanidines R1C（O）N=C[N（H）R2]NR23（R1=Mes or Ph; R2=Ar′′or Ar′; R3=Cy, Bn, iPr, or Et）（Mes=2,4,6-Me3C6H2, Ar′′=2,6-iPr2C6H3, Ar′=2,6-Me2C6H3） was synthesized from the reactions of parent acylthioureas with respective secondary amines. According to structutral characterization by single-crystal X-ray diffraction, the rough reduction of the steric hindrance of R substitutents of R1 C（O）N=C[N（H）R2]NR23（also abbreviated as R1-R2-R3 for comparison purposes） led to the slight enlongation of N（1）–C（1） bond lengthes and small decrease of N（1）–C（1）–N（3） bond angles from Mes–Ar′′–Cy（1） to Ph–Ar′′–Bn（2）, Ph–Ar′′–iPr（3） and Ph–Ar′–Cy（4）. At the same time, the N（1）–H（1）···O（1） intramolecular hydrogen bonds were observed in these cases. When R3=Et, an interesting compound Ph-Ar′-Et（5） was obtained with the formation of intermolecular hydrogen bonds instead. 1 belongs to the monoclinic system, space group P2（1/n） with a=9.6488（3）, b=28.5318（8）, c=11.9155（3） A, b=91.439（2）°, V=3279.27（16） A3, and Z=4. 2 belongs to the triclinic system, space group P1 with a=9.6759（7）, b=10.8613（8）, c=15.7642（12） A, a=70.429（3）, b=79.257（4）, g=69.052（4）°, V=1453.63（19） A3 and Z=2. 3 belongs to the monoclinic system, space group P2（1/c） with a=11.1393（4）, b=13.0643（4）, c=17.6600（6） A, b=101.866（2）o, V=2515.09（15） A3 and Z=4. 4 belongs to the monoclinic system, space group C2/c with a=17.8466（3）, b=13.6126（2）, c=21.6710（4） A, b=90.7310（10）°, V=4992.72（14） A3 and Z=8. 5 is of orthorhombic system, space group P212121 with a=10.5555（2）, b=11.8913（2）, c=14.9558（4） A, V=1877.23（5） A3 and Z=4.

An unexpected stereochemical effect of thio-substituted Asp in native chemical ligation

This study presents an unexpected finding that the cis isomer of β-thio-Asp exhibits higher ligation ac-tivity than the trans isomer.This discovery sheds light on the intricate nature of native chemical ligation and highlights the importance of factors beyond the steric effects of the side chain in modulating ligation activity.

pH-responsive aldehyde-bearing cyclometalated iridium(Ⅲ) complex for tracking intracellular pH fluctuations under external stimulation

Intracellular p H undertakes critical functions in various biological and pathological processes. It is important to monitor intracellular p H fluctuations for understanding physiological and pathological processes.Here, one aldehyde-bearing cyclometalated iridium(Ⅲ) complex([(4-pba)_(2)Ir(dcphen)]PF_(6), 4-pba = 4-(2-pyridyl) benzaldehyde, dcphen = 4,7-dichloro-1,10-phenanthroline, probe 1) was synthesized and used to track intracellular p H fluctuations. Probe 1 displayed p H-dependent luminescence property in p H range of 1.81–6.81 with an evaluated p Kavalue of 4.30 in BR buffer-DMSO(v:v = 99:1). An intramolecular hydrogen bonds assisted p H-responsive mechanism was proposed for the p H-responsive behavior of probe1. Probe 1 was successfully applied for imaging and tracking p H fluctuations in He La cells under external stimulation with fast response time, good photostability as well as low cytotoxicity and high cell permeability. This work demonstrates that aldehyde-bearing cyclometalated iridium(Ⅲ) complex can be used as alternative p H-responsive probe for real-time tracking intracellular p H fluctuations, which provides a strategy for the design of p H-responsive probe in versatile applications.

Synthesis and Optical Property of a New Zinc Complex Based on the Derivative of 2-(2’-Hydroxyphenyl)-1H-benzimidazole and Phenanthroline

A novel zinc complex(ZnE) has been designed and synthesized based on the derivative of 2-(2’-hydroxyphenyl)-1-H-benzimidazole(HBI) and the neutral nitrogen-containing ligand(phen). The crystal of the title complex crystallizes in the monoclinic system, space group P2_(1)/n with a = 10.2631(2), b = 34.2166(6), c = 11.4103(3) A, β = 96.771(2)°, M_(r )= 844.24, V = 3978.99(14) A^(3), Z = 4, the final R = 0.0400 and wR = 0.1001 for 8107 observed reflections(I > 2σ(I)). In the title complex, the free protonated phenoxide moiety(4-OH) is successfully retained to realize pseudo-intramolecular hydrogen bonds with the coordinated O atom from the other ligand.