Showing papers on "Hydrogen bond published in 2019"
TL;DR: In the thymol-menthol system, an abnormal strong interaction was identified stemming from the acidity difference of the phenolic and aliphatic hydroxyl groups, which is found to be the key to prepare non-ionic DES.
215 citations
TL;DR: The structure of the strong Brønsted acid site for a sulfated zirconium-based metal–organic framework has been shown to consist of a specific arrangement of adsorbed water and sulfate moieties on the zir Conium clusters.
Abstract: It remains difficult to understand the surface of solid acid catalysts at the molecular level, despite their importance for industrial catalytic applications. A sulfated zirconium-based metal-organic framework, MOF-808-SO4, was previously shown to be a strong solid Bronsted acid material. In this report, we probe the origin of its acidity through an array of spectroscopic, crystallographic and computational characterization techniques. The strongest Bronsted acid site is shown to consist of a specific arrangement of adsorbed water and sulfate moieties on the zirconium clusters. When a water molecule adsorbs to one zirconium atom, it participates in a hydrogen bond with a sulfate moiety that is chelated to a neighbouring zirconium atom; this motif, in turn, results in the presence of a strongly acidic proton. On dehydration, the material loses its acidity. The hydrated sulfated MOF exhibits a good catalytic performance for the dimerization of isobutene (2-methyl-1-propene), and achieves a 100% selectivity for C8 products with a good conversion efficiency.
174 citations
TL;DR: The surprising finding that sufficiently polarized C–H bonds can work even better in molecular receptors designed to capture anions such as chloride is reported, and a chloride-selective receptor in the form of a cryptand-like cage using only CH hydrogen bonding is designed.
Abstract: Tight binding and high selectivity are hallmarks of biomolecular recognition. Achieving these behaviors with synthetic receptors has usually been associated with OH and NH hydrogen bonding. Contrary to this conventional wisdom, we designed a chloride-selective receptor in the form of a cryptand-like cage using only CH hydrogen bonding. Crystallography showed chloride stabilized by six short 2.7-angstrom hydrogen bonds originating from the cage’s six 1,2,3-triazoles. Attomolar affinity (1017 M–1) was determined using liquid-liquid extractions of chloride from water into nonpolar dichloromethane solvents. Controls verified the additional role of triazoles in rigidifying the three-dimensional structure to effect recognition affinity and selectivity: Cl– > Br– > NO3– > I–. This cage shows anti-Hofmeister salt extraction and corrosion inhibition.
139 citations
TL;DR: The first application of dicationic tellurium‐based chalcogen bond donors in the nitro‐Michael reaction between trans‐β‐nitrostyrene and indoles constitutes the first activation of nitro derivatives by chalCogen bonding (and halogen bonding).
Abstract: Chalcogen bonding is the non-covalent interaction between Lewis acidic chalcogen substituents and Lewis bases. Herein, we present the first application of dicationic tellurium-based chalcogen bond donors in the nitro-Michael reaction between trans-β-nitrostyrene and indoles. This also constitutes the first activation of nitro derivatives by chalcogen bonding (and halogen bonding). The catalysts showed rate accelerations of more than a factor of 300 compared to strongly Lewis acidic hydrogen bond donors. Several comparison experiments, titrations, and DFT calculations support a chalcogen-bonding-based mode of activation of β-nitrostyrene.
126 citations
TL;DR: A strategy for design and synthesis of COF with flexible alkyl amine as a building block and intramolecular hydrogen bonding as a knot in the network is reported, which suggested that the materials could be applied to the removal of metallic ions in the future.
Abstract: There are several researches on the preparation and application of hydrazone-linked covalent organic frameworks (COFs), and all of them generally necessitate rigid aromatic amines. Herein, we report a strategy for design and synthesis of COF with flexible alkyl amine as a building block and intramolecular hydrogen bonding as a knot in the network. The proof-of-concept design was demonstrated by exploring 1,3,5-triformylphloroglucinol and oxalyldihydrazide (ODH) as precursors to synthesize a novel COF material (TpODH), in which different organic building units are combined through hydrazone bonds to form two-dimensional porous frameworks. It should be pointed that irreversible enol-to-keto tautomerism and intramolecular N-H···O═C hydrogen bonding of TpODH would enhance the crystallinity and chemical stability, leading to large specific surface area of 835 m2 g-1. However, another COF synthesized with 1,3,5-triformylbenzene and ODH exhibited less crystallinity and low special surface area (94 m2 g-1). Representatively, the resulting TpODH afforded Cu(II) and Hg(II) capacities of 324 and 1692 mg g-1, respectively, which exceeded that of most COFs previously reported. Moreover, the Fourier-transform infrared and X-ray photoelectron spectroscopy spectra analyses were taken to demonstrate the adsorption mechanism. These results suggested that the materials could be applied to the removal of metallic ions in the future.
120 citations
TL;DR: Deep eutectic solvents (DESs) consisting of cholinium chloride (ChCl) and alcohols have been widely applied in the purification of bioactive compounds, biodiesel, and flavonoids.
Abstract: Deep eutectic solvents (DESs) consisting of cholinium chloride (ChCl) and alcohols have been widely applied in the purification of bioactive compounds, biodiesel, and flavonoids. However, an explic...
98 citations
TL;DR: High-resolution solid-state NMR spectroscopy shows water interacting with zeolite Brønsted acid sites, converting them to hydrated hydronium ions over a wide range of temperature and thermodynamic activity of water.
Abstract: The catalytic sites of acidic zeolite are profoundly altered by the presence of water changing the nature of the Bronsted acid site. High-resolution solid-state NMR spectroscopy shows water interacting with zeolite Bronsted acid sites, converting them to hydrated hydronium ions over a wide range of temperature and thermodynamic activity of water. A signal at 9 ppm was observed at loadings of 2–9 water molecules per Bronsted acid site and is assigned to hydrated hydronium ions on the basis of the evolution of the signal with increasing water content, chemical shift calculations, and the direct comparison with HClO4 in water. The intensity of 1H–29Si cross-polarization signal first increased and then decreased with increasing water chemical potential. This indicates that hydrogen bonds between water molecules and the tetrahedrally coordinated aluminum in the zeolite lattice weaken with the formation of hydronium ion–water clusters and increase the mobility of protons. DFT-based ab initio molecular dynamics ...
98 citations
TL;DR: The two systems described here show that the HBeXB concept extends the range of interaction energies and geometries to be significantly greater than that of the XB alone.
Abstract: The halogen bond (XB) has become an important tool for molecular design in all areas of chemistry, including crystal and materials engineering and medicinal chemistry. Its similarity to the hydrogen bond (HB) makes the relationship between these interactions complex, at times competing against and other times orthogonal to each other. Recently, our two laboratories have independently reported and characterized a synergistic relationship, in which the XB is enhanced through direct intramolecular HBing to the electron-rich belt of the halogen. In one study, intramolecular HBing from an amine polarizes the iodopyridinium XB donors of a bidentate anion receptor. The resulting HB enhanced XB (or HBeXB) preorganizes and further augments the XB donors. Consequently, the affinity of the receptor for halogen anions was significantly increased. In a parallel study, a meta-chlorotyrosine was engineered into T4 lysozyme, resulting in a HBeXB that increased the thermal stability and activity of the enzyme at elevated temperatures. The crystal structure showed that the chlorine of the noncanonical amino acid formed a XB to the protein backbone, which augmented the HB of the wild-type enzyme. Calorimetric analysis resulted in an enthalpic contribution of this Cl-XB to the stability of the protein that was an order of magnitude greater than previously determined in biomolecules. Quantum mechanical (QM) calculations showed that rotating the hydroxyl group of the tyrosine to point toward rather than away from the halogen greatly increased its potential to serve as a XB donor, equivalent to what was observed experimentally. In sum, the two systems described here show that the HBeXB concept extends the range of interaction energies and geometries to be significantly greater than that of the XB alone. Additionally, surveys of structural databases indicate that the components for this interaction are already present in many existing molecular systems. The confluence of the independent studies from our two laboratories demonstrates the reach of the HBeXB across both chemistry and biochemistry and that intentional engineering of this enhanced interaction will extend the applications of XBs beyond these two initial examples.
94 citations
TL;DR: The introduction of hydroxyl groups and n-butyl groups into COF-4-OH for the construction of COFs with strong dual emission was demonstrated.
Abstract: Here we reveal the effects of hydrogen bonds and alkyl groups on the structure and emission of covalent organic frameworks (COFs). Hydrogen bonds improve molecular rigidity leading to high crystallinity and restrict intramolecular rotation to enhance the emission of COFs. An excited-state intramolecular proton transfer (ESIPT) effect for dual emission is achieved via the intramolecular hydrogen bonds between hydroxyl groups and imine bonds. Alkyl groups increase interlayer spacing as a natural "scaffold" and achieve a staggered AB stacking mode to decrease aggregation-caused quenching. Based on the above guidance, COF-4-OH with strong emission is prepared with 2,4,6-triformylphloroglucinol (TFP) and 9,9-dibutyl-2,7-diaminofluorene (DDAF). Strong dual emission is observed and used to differentiate organic solvents with different polarities, to determine the water content in organic solvents, and to detect different pH levels. Our work serves as a guide for the rational design of functional monomers for the preparation of emissive COFs.
93 citations
TL;DR: One mononuclear Ni(II) complex [Ni(L1)(MeOH)2]·MeOH (1) and two novel trinuclear Ni (II) complexes [Ni3(L2)3(EtOH)6] (2) and [Ni 3(L 2) 3(H2O)6], constructed from symmetric N2O2-donors chelating ligands (H2L1 and H2L2), were synthesized and characterized by elemental analyses, FT-IR, UV-Vis spectra and
90 citations
TL;DR: It is demonstrated how these energetic factors are essential in a correct description of the hydrogen bond, and several examples of systems whose energetic and geometrical features are not captured by easy-to-use predictive models are discussed.
Abstract: Hydrogen bonds are a complex interplay between different energy components, and their nature is still subject of an ongoing debate. In this minireview, we therefore provide an overview of the different perspectives on hydrogen bonding. This will be done by discussing the following individual energy components: 1) electrostatic interactions, 2) charge-transfer interactions, 3) π-resonance assistance, 4) steric repulsion, 5) cooperative effects, 6) dispersion interactions and 7) secondary electrostatic interactions. We demonstrate how these energetic factors are essential in a correct description of the hydrogen bond, and discuss several examples of systems whose energetic and geometrical features are not captured by easy-to-use predictive models.
TL;DR: A hydrogen-bond stabilized organic battery framework illustrated for 2,5-diamino-1,4-benzoquinone (DABQ), an electrically neutral and low mass organic chemical, yet with unusual thermal stability and low solubility in battery electrolytes.
Abstract: Small organic materials are generally plagued by their high solubility in battery electrolytes. Finding approaches to suppress solubilization while not penalizing gravimetric capacity remains a challenge. Here we propose the concept of a hydrogen bond stabilized organic battery framework as a viable solution. This is illustrated for 2,5-diamino-1,4-benzoquinone (DABQ), an electrically neutral and low mass organic chemical, yet with unusual thermal stability and low solubility in battery electrolytes. These properties are shown to arise from hydrogen bond molecular crystal stabilization, confirmed by a suite of techniques including X-ray diffraction and infrared spectroscopy. We also establish a quantitative correlation between the electrolyte solvent polarity, molecular structure of the electrolyte and DABQ solubility – then correlate these to the cycling stability. Notably, DABQ displays a highly reversible (above 99%) sequential 2-electron electrochemical activity in the solid phase, a process rarely observed for similar small molecular battery chemistries. Taken together, these results reveal a potential new strategy towards stable and practical organic battery chemistries through intramolecular hydrogen-bonding crystal stabilization.
TL;DR: A supramolecular polymeric adhesive prepared from non-viscous, non-polymeric materials by water-participant hydrogen bonds displays strong, reversible adhesion to hydrophilic surfaces, a property that forecasts the application of hydrogen bonding in advanced supramolescular materials.
Abstract: A supramolecular polymeric adhesive was prepared from non-viscous, non-polymeric materials by water-participant hydrogen bonds. Pt-pyridine coordination and water-crown ether hydrogen bonding combine to effect the supramolecular polymerization. The supramolecular polymeric adhesive displays strong, reversible adhesion to hydrophilic surfaces, a property that forecasts the application of hydrogen bonding in advanced supramolecular materials.
TL;DR: The different hydrogen bond interactions in two organic-inorganic hybrid manganese halide compounds, namely [A]2[MnBr4] (A = N-butyl-N-methylpyrrolidinium]) lead to distinct photoluminescence quantum yields.
TL;DR: The use of the palladium-catalyzed inter-and/or intra-molecular C-H bond arylations in the building of various π-extended (hetero)aromatic structures has emerged as a suitable alternative to the previous multi-step synthesis as discussed by the authors.
TL;DR: In this paper, a novel strategy is established to synthesize Mo-doped graphitic carbon nitride (g-C3N4) with excellent photocatalytic activity through a green approach of biological template.
Abstract: Herein, a novel strategy is established to synthesize Mo-doped graphitic carbon nitride (g-C3N4) with excellent photocatalytic activity through a green approach of biological template. The addition of biotemplates provides a microenvironment for the formation of hydrogen bonds in which the flower-like g-C3N4 is formed by self-assembly between precursors, which not only increases the specific surface area of the material but also exposes more catalytic activity edge. Benefiting from the non-localized of Mo(VI) 4d orbital, Mo-doped g-C3N4 constructs a suitable band structure and a built-in electric field that promotes electron delocalization, which improves the absorption range of visible light and separation efficiency of photo-generated electron-hole pairs. Subsequently, a possible chelation-hydrogen bond coordination mechanism was proposed based on the characterization results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and 15N solid-state NMR (15N NMR). As a result, the π-conjugated system of g-C3N4 was extended by forming a chelate centered on Mo(VI). Photocatalytic hydrogen evolution (PHE) showed that the optimal hydrogen evolution rate of Mo-doped g-C3N4 was as high as 2008.9 umol/g·h, which was 9.6 times than that of bulk g-C3N4.
TL;DR: In this paper, the authors show that self-healing polymers with micro-phase-separated structure are plagued with inferior selfhealing efficiency at room temperature due to a lack of dynamic interactions in hard domains.
Abstract: Self-healing polymers with microphase-separated structure are plagued with inferior self-healing efficiency at room temperature due to a lack of dynamic interactions in hard domains. Herein, we des...
TL;DR: New approaches to self-healing, proper characterization methods for dynamic noncovalent bonds, and demonstration of simulations are introduced.
Abstract: Synthesis and comprehensive examination of a polyurethane (urea) elastomer that self-heals based on intrinsic dynamic non-covalent bonds (van der Waals and hydrogen) are reported. The dynamic non-covalent bonds include hydrogen bonds and van der Waals forces. The difference in the previous approach in which hydrogen bond self-healing materials introduced dense quadruple hydrogen bonds at the ends or branched chains poly(propylene carbonate) (PPC) diol was used as the soft segment of the polyurethane (urea) material, and strong van der Waals forces were provided by the large number of carbonyl groups in its main chain; hydrogen bonds were formed by urethane bonds, urea bonds, and the carbonyl groups on PPC. The mechanical properties and healing efficiency of the self-healing polyurethane (urea) elastomer were studied. In situ temperature-dependent infrared and low-field nuclear magnetic resonance (LNMR) measurements were combined with molecular dynamics simulations to investigate the self-healing mechanisms. The results of the studies on the self-healing polyurethane demonstrate that the dynamic cross-linking between hydrogen bonds and van der Waals forces is the basic driving force for the self-healing ability of the material, and temperature is the key factor that affects hydrogen bonding and van der Waals forces. The effect of crystallization on the self-healing ability of the material was also studied. The molecular dynamics simulation results also demonstrate interplay between van der Waals forces and hydrogen bonds at different temperatures.
TL;DR: Results from an ensuing experimental investigation into the G9a-like protein (GLP)-inhibitor complex demonstrated that N+-C-H···O hydrogen bonds affect the activity of the inhibitors against the target enzyme should provide the basis for the use of N+.
Abstract: In the context of drug design, C-H···O hydrogen bonds have received little attention so far, mostly because they are considered weak relative to other noncovalent interactions such as O-H···O hydrogen bonds, π/π interactions, and van der Waals interactions. Herein, we demonstrate the significance of hydrogen bonds between C-H groups adjacent to an ammonium cation and an oxygen atom (N+-C-H···O hydrogen bonds) in protein-ligand complexes. Quantum chemical calculations revealed details on the strength and geometrical requirements of these N+-C-H···O hydrogen bonds, and a subsequent survey of the Protein Data Bank (PDB) based on these criteria suggested that numerous protein-ligand complexes contain such N+-C-H···O hydrogen bonds. An ensuing experimental investigation into the G9a-like protein (GLP)-inhibitor complex demonstrated that N+-C-H···O hydrogen bonds affect the activity of the inhibitors against the target enzyme. These results should provide the basis for the use of N+-C-H···O hydrogen bonds in drug discovery.
TL;DR: Electrostatic charges patterning along crystalline channels recognize CO2 with high selectivity and promote its fast screwing dynamics through the crystal at one million steps per second, strongly reminiscent of trans-membrane transport in biological channels.
Abstract: Porous molecular materials represent a new front in the endeavor to achieve high-performance sorptive properties and gas transport. Self-assembly of polyfunctional molecules containing multiple charges, namely, tetrahedral tetra-sulfonate anions and bifunctional linear cations, resulted in a permanently porous crystalline material exhibiting tailored sub-nanometer channels with double helices of electrostatic charges that governed the association and transport of CO2 molecules. The charged channels were consolidated by robust hydrogen bonds. Guest recognition by electrostatic interactions remind us of the role played by the dipolar helical channels in regulatory biological membranes. The systematic electrostatic sites provided the perfectly fitting loci of complementary charges in the channels that proved to be extremely selective with respect to N2 (S = 690), a benchmark in the field of porous molecular materials. The unique screwing dynamics of CO2 travelling along the ultramicropores with a step-wise reorientation mechanism was driven by specific host–guest interactions encountered along the helical track. The unusual dynamics with a single-file transport rate of more than 106 steps per second and an energy barrier for the jump to the next site as low as 2.9 kcal mol−1 was revealed unconventionally by complementing in situ13C NMR anisotropic line-shape analysis with DFT modelling of CO2 diffusing in the crystal channels. The peculiar sorption performances and the extraordinary thermal stability up to 450 °C, combined with the ease of preparation and regeneration, highlight the perspective of applying these materials for selective removal of CO2 from other gases.
TL;DR: An in-depth analysis of the arrangement and ordering of its components at molecular level is presented to understand the structural morphology of ethaline using optimum force-field parameters for EG recently proposed by the group.
Abstract: Atomistic molecular dynamics simulations have been performed to investigate the microscopic structure of ethaline deep eutectic solvent (DES), a mixture of choline chloride ([Ch][Cl]) and ethylene glycol (EG) in molar ratio of 1:2, respectively. As much as the structure of a DES is derived by the composition of the species present in it, the chemical nature of the hydrogen bond donor species involved also plays a crucial role in laying down the microscopic structure of DESs. By virtue of its inherent chemical structure, EG renders both intra- and intermolecular hydrogen bonds. Therefore, the molecular level structural landscape of DESs containing EG as hydrogen bond donor is reckoned to be a bit complex. In the present study, we aim to understand the structural morphology of ethaline using optimum force-field parameters for EG recently proposed by our group. After an initial assessment of the refined force-field parameters for ethaline DES, we have presented an in-depth analysis of the arrangement and ordering of its components at the molecular level. Simulated X-ray scattering structure function and its partial components reveal the presence of short-range as well as long-range interactions in ethaline. The role of hydrogen bonding interactions among all the three species [Ch]+, [Cl]-, and EG was predominantly observed through radial and radial-angular distribution functions and substantiated by spatial distribution functions. The observation of the competitive nature of [Ch]+ and EG to form a hydrogen bond with the anion is one of the major outcomes of the present study. Also, weaker intra- and intermolecular hydrogen bonding interactions between EG molecules were seen along with their simultaneous involvement with the ammonium group of the choline cation.
TL;DR: It has been shown that the combination of a simple directing group and a 2-pyridone ligand favours six-membered cyclopalladation, demonstrating the feasibility of using geometric strain to reverse conventional site selectivity in C(sp3)–H activation.
Abstract: One of the core barriers to developing C-H activation reactions is the ability to distinguish between multiple C-H bonds that are nearly identical in terms of electronic properties and bond strengths. Through recognition of distance and molecular geometry, remote C(sp2)-H bonds have been selectively activated in the presence of proximate ones. Yet achieving such unconventional site selectivity with C(sp3)-H bonds remains a paramount challenge. Here we report a combination of a simple pyruvic acid-derived directing group and a 2-pyridone ligand that enables the preferential activation of the distal γ-C(sp3)-H bond over the proximate β-C(sp3)-H bonds for a wide range of alcohol-derived substrates. A competition experiment between the five- and six-membered cyclopalladation step, as well as kinetic experiments, demonstrate the feasibility of using geometric strain to reverse the conventional site selectivity in C(sp3)-H activation.
TL;DR: In this paper, the authors showed that the ZIF-8 phase shift substance is of crystalline structure but does not belong to any known pseudo-polymorphs of ZIF, ZIFL, dia(Zn), or decomposed product of Zif-8: Zn(OH) 2 and 2-methylimidazole.
TL;DR: Hydrogen bond engineering is an effective strategy to modify the structure and properties of polymers for various applications and is demonstrated to have an extremely high hydrogen-evolution rate.
Abstract: Unlike graphene, graphitic carbon nitride (CN) polymer contains a weak hydrogen bond and van der Waals (vdWs) interactions besides a strong covalent bond, which controls its final morphology and functionality. Herein, we propose a novel strategy, hydrogen-bond engineering, to tune hydrogen bonds in polymeric CN through nonmetal codoping. Incorporation of B and P dopants breaks partial hydrogen bonds within the layers and simultaneously weakens the vdWs interaction between neighboring layers, resulting in ultrathin codoped CN nanosheets. The two-dimensional structure of the ultrathin sheet, broken hydrogen bonds, and incorporated dopants endow them with efficient visible light harvesting, improved charge separation, and increased active edge sites that synergistically enhance the photocatalytic activity of doped CN. Specifically, the B/P-codoped CN exhibits an extremely high hydrogen-evolution rate of 10877.40 μmol h–1 g–1, much higher than most reported values of CN. This work demonstrates that hydrogen b...
TL;DR: The heat-induced hydrogen bonding evolution in the sodium alginate (SA) film is explored mainly by FTIR spectroscopy in combination with perturbation correlation moving window (PCMW) technique and 2D correlation spectroscopic (2Dcos).
TL;DR: Aggregation-caused quenching (ACQ) has long been a problem that inhibits the application of organic light emitting materials in organic light-emitting diodes, especially near-infrared (NIR) materia as mentioned in this paper.
Abstract: Aggregation-caused quenching (ACQ) has long been a problem that inhibits the application of organic light-emitting materials in organic light-emitting diodes, especially near-infrared (NIR) materia...
TL;DR: It is demonstrated that water at low relative humidity binds initially to open metal sites and subsequently forms disconnected one-dimensional chains of hydrogen-bonded water molecules bridging between cobalt atoms.
Abstract: Water in confinement exhibits properties significantly different from bulk water due to frustration in the hydrogen-bond network induced by interactions with the substrate. Here, we combine infrared spectroscopy and many-body molecular dynamics simulations to probe the structure and dynamics of confined water as a function of relative humidity within a metal-organic framework containing cylindrical pores lined with ordered cobalt open coordination sites. Building upon the agreement between experimental and theoretical spectra, we demonstrate that water at low relative humidity binds initially to open metal sites and subsequently forms disconnected one-dimensional chains of hydrogen-bonded water molecules bridging between cobalt atoms. With increasing relative humidity, these water chains nucleate pore filling, and water molecules occupy the entire pore interior before the relative humidity reaches 30%. Systematic analysis of rotational and translational dynamics indicates heterogeneity in this pore-confined water, with water molecules displaying variable mobility as a function of distance from the interface.
TL;DR: This study found that the lowest lying excited state (S1) of DM-7HIT is a sulfur nonbonding (n) to π* transition, which undergoes O-H bond flipping from S1(nπ*) to the non-H-bonded S'1( nπ*) state, followed by intersystem crossing and internal conversion to populate the T'1(* state.
Abstract: We report O–H----S hydrogen-bond (H-bond) formation and its excited-state intramolecular H-bond on/off reaction unveiled by room-temperature phosphorescence (RTP). In this seminal work, this phenom...
TL;DR: It is found that the strong intermolecular C=O…H-C hydrogen bonds between Cz2BP and chloroform in cocrystal decrease the non-radiative decay rate of T1→S0 by 3-6 orders of magnitude due to the vibronic decoupling effect on theC=O stretching motion and the increase of (π,π*) composition in T1 state.
Abstract: Organic room-temperature phosphorescence (RTP) is generally only exhibited in aggregate with strong dependence on morphology, which is highly sensitive to the intermolecular hydrogen bonding interaction. Here, 4,4'-bis(9H-carbazol-9-yl)methanone (Cz2BP), emitting RTP in a cocrystal consisting of chloroform but not in the amorphous nor in the crystal phase, was investigated to disclose the morphology dependence through molecular dynamics simulations and first-principles calculations. We find that the strong intermolecular C═O···H-C hydrogen bonds between Cz2BP and chloroform in cocrystals decrease the nonradiative decay rate of T1 → S0 by 3-6 orders of magnitude due to the vibronic decoupling effect on the C═O stretching motion and the increase of (π,π*) composition in the T1 state. The former is responsible for high efficiency and the latter for long-lived RTP with a calculated lifetime of 208 ms (exp. 353 ms). Nevertheless, the weak hydrogen bonds cannot cause any appreciable RTP in amorphous and crystal phases. This novel understanding opens a way to design organic RTP materials.