Guest Absorption Research Articles

Molecular Recognition of Aromatics in Spherical Nanocages.

In general, due to the lack of efficient specific molecular interactions, achieving host-guest molecular recognition inside large and neutral metal organic cages (MOCs) is challenging. Preferential molecular recognition of aromatics using the internal binding sites of interlocked icosahedral (i.e., spherical) M12L8MOCs within poly-[n]-catenane (1) is reported. The guest absorption has been monitored directly in the solid-state by consecutive single-crystal-to-single-crystal (SCSC) reactions in a gas-solid environment, using single-crystal X-ray diffraction (SC-XRD) experiments. The preferential guest uptake is corroborated by Density Functional Theory (DFT) calculations by determining the host-guest interaction energy (Ehost-guest) with the nitrobenzene (NB) >> p-xylene (p-xy) >> o-dichlorobenzene (o-DCB) trend (i.e., from 44 kcal/mol to 25 kcal/mol), assessing the XRD outcomes. Combining SC-XRD, DFT and solid-state 13C NMR, the exceptional stability of the M12L8 cages, together with the guest exchange/release properties are rationalized by the presence of mechanical bonds (efficient π-π interactions) and by the pyridine's rotor-like behaviour (with 3 kcal/mol rotational energy barrier). The structure-function properties of M12L8 makes 1 a potential candidate in the field of molecular sensors.

White Light-Emitting Electrochemical Cells Employing Phosphor-Sensitized Thermally Activated Delayed Fluorescence to Approach All-Phosphorescent Device Efficiencies.

Solid-state light-emitting electrochemical cells (LECs) show promising advantages of simple device architecture, low operation voltage, and insensitivity to the electrode work functions such that they have high potential in low-cost display and lighting applications. In this work, novel white LECs based on phosphor-sensitized thermally activated delayed fluorescence (TADF) are proposed. The emissive layer of these white LECs is composed of a blue-green phosphorescent host doped with a deep-red TADF guest. Efficient singlet-to-triplet intersystem crossing (ISC) on the phosphorescent host and the subsequent Förster energy transfer from the host triplet excitons to guest singlet excitons can make use of both singlet and triplet excitons on the host. With the good spectral overlap between the host emission and the guest absorption, 0.075 wt.% guest doping is sufficient to cause substantial energy transfer efficiency (ca. 40 %). In addition, such a low guest concentration also reduces the self-quenching effect and a high photoluminescence quantum yield of up to 84 % ensures high device efficiency. The phosphor-sensitized TADF white LECs indeed show a high external quantum efficiency of 9.6 %, which is comparable with all-phosphorescent white LECs. By employing diffusive substrates to extract the light trapped in the substrate, the device efficiency can be further improved by ca. 50 %. In the meantime, the intrinsic EL spectrum and device lifetime of the white LECs recover since the microcavity effect is destroyed. This work successfully demonstrates that the phosphor-sensitized TADF white LECs are potential candidates for efficient white light-emitting devices.

A novel magnetic loading porous liquid absorbent for removal of Cu(II) and Pb(II) from the aqueous solution

The first example of a magnetic loading functional porous liquid (PL) by employing hollow silicon dioxide (HS) loaded with Fe3O4 as the porous guest, (3-glycidyloxypropyl) trimethoxysilane (KH560) and polyetheramine M2070 as hindered sterically solvents was demonstrated in this paper. This nanoadsorbent (Fe3O4@HS-PL) was prepared for the decontamination of aqueous solutions from Cu(II) and Pb(II) heavy metals. The hindered sterically solvents (i.e., the flexible oligomer chains) endow the Fe3O4@HS porous guest with a superior flowing behavior at ambient temperature. Various approaches were applied to confirm the morphology, structure and properties of the resultant Fe3O4@HS-PL. More significantly, the adsorption behavior of Cu(II) and Pb(II) in aqueous solution by Fe3O4@HS-PL was studied in detail. As expected, combined with the cavity structure from porous guest and amine groups from flexible organic flow layer, Fe3O4@HS-PL exhibited excellent adsorption capacities of 322.58 and 357.14 mg·g−1 for Cu(II) and Pb(II), respectively, at 298 K, pH 8 and initial concentration of 20 mg·L-1. The obtained HS and Fe3O4 in Fe3O4@HS-PL magnetic nanoadsorbent presented average particles size ascertained to be ca.200 nm and 30 nm, respectively. Moreover, the Freundlich model and pseudo-first-order model has described the adsorption process and adsorption kinetics. The parameters in thermodynamic experiment signified the spontaneity and endothermic properties of the adsorption. Moreover, magnetic loading endowed the Fe3O4@HS-PL with a superior regeneration performance. A variety of mechanisms containing coordination interaction, porous guest absorption, electrostatic interaction, steric effect and entropy are simultaneously realized in this novel adsorption system. Therefore, the introduction of PLs adsorbents into heavy metal adsorption systems through the construction of PLs materials by magnetic loading and surface amination is of great significance in the field of heavy metal adsorption, eventually starting a new time of pushing forward the development of novel adsorbents for decontamination of aqueous solutions from heavy metal ions.

Strategy to modulate the singlet-triplet energy gap for spiro-based thermally activated delayed fluorescence molecules

The energy gap between singlet and triplet states plays an important role in determining the reverse intersystem crossing (RISC) process for thermally activated delayed fluorescence (TADF) molecules, ingenious strategy to modulate the singlet-triplet energy gap is highly desired. In this work, the photophysical properties of eleven TADF molecules are theoretically investigated, which are composed of 9,10-dihydro-10-phenylacridine as an electron donor and various electron acceptor units based on spiro donor-acceptor structure as well as adopting the indene-carbazole unit as the bridging body. Two new proposed calculation methods are applied. The method of overlapping integral and ΔEst, is used to screen efficient TADF molecules, and the optimal Hartree-Fock method is adopted to investigate the excited state properties for promising TADF molecules. Results show that different substituents in the indene-carbazole unit are distinctive in modulating the singlet-triplet energy gaps and the emission colors. Moreover, two promising TADF molecules with purple and blue emission are detected and the performances of emitting molecules in host matrix are theoretically investigated. Remarkable spectral overlap between host emission and guest absorption can be found and efficient energy transfer from host to guest is expected. Furthermore, the charge transfer properties are revealed based on Marcus equation, excellent hole and electron transfer properties are detected, which are comparable with these experimental detected molecules. Our molecular design strategy could provide a rational approach to regulate the emission and energy transfer as well as charge transfer properties, two promising TADF molecules with purple and blue emission are theoretically proposed.

Structural behavior of organic zeolites on guest sorption/desorption

The term organic zeolites, originally has been introduced to chemical literature by R.M. Barrer, to describe molecular crystals having open porous structures, able to reversibly absorb and desorb organic species with relatively weak, if any, sorption of water or other hydrophilic molecules. A characteristic feature of the organic zeolite structures, when compared to classical `inorganic' zeolites based on aluminosilicates, is the relatively weak intermolecular bonding within the host component. This is the reason for significant flexibility of the host crystal structure which changes its parameters upon guest absorption, desorption or exchange. The most characteristic property in this respect is absorption with `adsorbate generated sorption sites' which is the basis for design and control of selectivity and efficiency of sorption-desorption processes. In general, organic zeolite behavior may be observed on a large variety of supramolecular materials, including solvates of macrocyclic compounds and in the very important, so-called- MOFs. In the paper solvation of cyclodextrins and their complexes will be used as the convenient example, based on brand new, mostly yet unpublished large structures of heavily solvated cyclodextrin complexes in the solid state. Cyclodextrins are commonly known as materials having intra-molecular cavity able to accommodate guest species. This property, when combined with sorption in the inter-molecular space in the solid state structures of CDs leads to very interesting structures and properties. In general, such behavior may be observed only when CD moieties are at equilibrium with a solution of the respective guest and solvent species. The equilibria are quite sensitive to minor changes of solution chemical composition what may be observed microscopically as morphology changes of the crystalline phases. This phenomenon will be illustrated with short movies demonstrating crystal behavior on change of its environment. Novel x-ray structures will also be demonstrated and commented. This work was supported by grant POIG.01.01.02-14-102/09.

Guest Inclusion Crystal structures of Macrocyclic Boronic Esters

Macrocyclic compound has been attracting increasing attention because of their application for guest absorption and storage, guest selectivity, and reaction environment, which would utilize void space in the compound. Recently, such macrocyclic compound, boronic esters, has found to be formed as dynamic self-assembly of organic molecules through solvent dependent dynamic covalent bond formation between racemic polyol and planar 1,4-benzen(boronic acid)[1]. Thus, it is important to determine the crystal structure of the macrocyclic boronic esters with incorporated guest molecule to reveal the features of the compounds. In this study, structures of boronic ester of 1,4- naphthalene(boronic acid) (1) are presented and compared. The boronic ester with toluene guest molecule crystalized in monoclinic system, C2/c, Z=4, V=5099.7(6) Å3. As expected, toluene molecule was accommodated within a ring sandwiched by two naphthalene rings suggesting π-π interaction (ca. 3.6 Å separations). It is interesting that other structures of 1 with 1,4-dicyanobenzene, chloroform, and THF also have isomorphic structures to 1 with toluene. It clearly shows the guest inclusion ability of this boronic ester by weak intermolecular interactions. In the crystal structures, the boronic ester aligned along b-axis forming one-dimensional stacking with channel structure filled with guest molecules. Also, 1 with chloroform has a pseudo-polymorph phase (P21/c, V=5780.8(13) Å3) that has two additional chloroform molecules inside and outside of the ring; however, it also shows similar one-dimensional stacking structure with channel, implying this boronic ester has an easily stacking molecular shape. Although, the molecules have similar [2+2] ring structure, dihedral angle between two facing naphthalene rings is different in 1 with toluene, which is smaller as 14.10than 22 to 240in other structures. It may indicate a flexibility of the macrocyclic ring.

Quantum chemical characterization and design of host materials based on phosphine oxide-substituted (triphenylamine) fluorene for (deep) blue phosphors in OLEDs

We studied the electronic structures of a series of fluorene derivatives (p/mPODPFs and p/mPOAPFs) using density functional theory calculations and investigated their performances as host materials in organic light-emitting diodes from three aspects, i.e. triplet energy, ability of charge injection from neighboring organic layer or electrode, and match of the hosts and the reference guests (FIrpic and FCNIr) for efficient energy transfer (EF). Especially for the last aspect, the singlet/triplet (S(1)/T(1)) energies as well as the simulated host emission and guest absorption spectra are investigated to predict the possible emission mechanisms in the host-guest system and therefore to pursue the most suitable host for (deep) blue guest. From the investigated results, we deduced that pPODPF and pPOAPF are suitable for sky-blue FIrpic due to feasible Förster/Dexter energy transfers from pPODPF/pPOAPF to FIrpic, which agrees well with the experimental results. Furthermore, the higher external quantum efficiency (20.6%) of the pPOAPF-based device than that of the pPODPF-based device (13.2%) in experiments was inferred to be attributed to the matching S(1) energies between pPOAPF and FIrpic as well as good hole/electron injection abilities of pPOAPF in spite of a smaller overlap between the pPOAPF emission and FIrpic absorption spectra. By contrast, mPOAPF and mPODPF, designed in the work, may match with deep-blue FCNIr. In particular, mPOAPF may exhibit good performance as a host material for deep blue FCNIr as a consequence of its own balanced hole/electron injection ability and the matching S(1)/T(1) energies between mPOAPF and FCNIr.

Cover Picture: Chiral Metallacrown Supramolecular Compartments that Template Nanochannels: Self‐Assembly and Guest Absorption (Chem. Asian J. 1/2010)

Molecular containers have drawn intense interest for their ability to selectively recognize and influence the chemistry of guest molecules. A host–guest chemistry approach to synthesizing large containers capable of absorbing large guests is presented. V. Pecoraro et al. show that LaIII[15--5] selectively recognizes saturated C7 and C8 dicarboxylates, with the guests bound to copper ring metals on the hydrophilic face of four metallocrown hosts. This unprecendented tetrameric metallocrown complex dimerizes through ligand side-chain interactions to form a novel octameric hydrophilic compartment that is accessible through a specific sized opening. For further details, turn to their Full Paper on page 46 ff.

Chiral Metallacrown Supramolecular Compartments that Template Nanochannels: Self‐Assembly and Guest Absorption

There is a report on the Hg contamination due to the waste glass coated with mercury dumped by a thermometer factory at Kodaikanal, Tamil Nadu. Water samples from various zones of the lake located at Kodaikanal were subjected for the spectrophotometric method of Hg content. The results have disclosed that there is an elevated level of Hg. The data was analysed statistically and discussed with relation to the contamination of Hg.

Syndiotactic Polystyrene Aerogels: Adsorption in Amorphous Pores and Absorption in Crystalline Nanocavities

Sorption experiments have been conducted for syndiotactic polystyrene (s-PS) aerogels with different crystalline forms and of different porosities. Nitrogen uptake experiments at 77 K have confirmed that δ-form aerogels present crystalline nanocavities as well as amorphous porosity. The equilibrium uptake of organic molecules, from dilute aqueous solutions, for δ-form aerogels is high (e.g., more than 5 wt % of 1,2-dichloroethane, DCE, from 1 ppm solutions) and independent of aerogel porosity. Gravimetric experiments, as well as FTIR conformational studies on absorbed DCE, clearly indicate that guest absorption from diluted solutions occurs only in the crystalline nanocavities. High-porosity δ-form aerogels (P > 98%) can also exhibit substantial water adsorption from the amorphous porosity, which is favorable to the pollutant absorption kinetics. In fact, apparent guest diffusivity increases of several orders of magnitude, with respect to the corresponding films, have been observed.

White polymeric light-emitting diode based on a fluorene polymer∕Ir complex blend system

Efficient white-polymeric light-emitting diodes (PLED) were fabricated as a single active layer containing blue-emitting poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl) endcapped with bis(4-methylphenyl)phenylamine; (PF2∕6am4), and yellow-orange-emitting iridium [tri-fluorenyl] pyridine complex [Ir(Fl3Py)3]. The fluorene-like ligands in the blended device prevent phase segregation and also enhance energy transfer from the polymer host to the guest due to efficient overlap of wave function (Dexter process) and host singlet emission and guest absorption bands (Förster process) which reduces the loading level required to produce white emission. The two emitted colors complement each other and doping levels of 2%–3% produce white emission. Above a certain current density, depending on the doping level, the device Commission Internationale de L’Eclairage (CIE) coordinates become bias independent and a stabilized white emission can be obtained. A white-emitting PLED (coordinates 0.348, 0.367) of peak external quantum efficiency of 2.8%, and luminance of 16000cd∕m2 at applied voltage of 5V (i.e., 4.57cd∕A) was obtained.

Optical Properties of Chemically Mixed Molecular Crystals

Abstract The substitutionally mixed crystal system of tetracene as guest in an anthracene host lattice has been reinvestigated with perturbation theory calcualations of intensity mixing. The effect of the actual misalignment of the guest molecules relative to the host lattice is appraised. Additional refinements in the calculations incorporate the higher energy host states and the initially mixed polarization of the free host and guest absorption bands. The results are compared to existing experimental data.

Absorption spectra of doped anthracene crystals. Determination of the direction of the transition moment of the dopant

Measurements of the polarised guest absorption as a function of the angle of incidence in mixed molecular crystals lead to the determination of an effective transition dipole moment for the guest. Local field effects appear to be only slightly anisotropic. The two guest spectra produced by 2-aminoanthracene in anthracene are shown to correspond to different orientations of the transition moment. Computer simulation of the crystal packing leads to an assignment of the spectra to specific orientations of the guest molecule and so fixes the direction of the transition moment with respect to molecular axes.

Study of host-guest interaction in mixed molecular crystals

The measurement of the polarization ratio (PR) of guest transitions in mixed molecular crystals has been used as a tool to study the effect of host-guest interaction. Two mixed crystal systems, namely naphthacene in trans-stilbene and anthracene in carbazole, have been studied. In the former system, the lowest energy host and guest transitions are oppositely polarized. It has been observed that in this system the ( b:a) PR value for the guest absorption system decreases progressively for the higher members of the vibronic bands as their energy difference from the host excited state decreases. This result quite convincingly demonstrates the effect of the host on a guest transition. In the latter system, the lowest energy host and guest transitions are polarized in the same direction, and in this system the ( b:a) PR value has been found to be more or less constant over the entire guest absorption band system. The results of the polarization measurement in these two mixed crystals are in conformity with the theory of host-guest interaction developed by Craig and Thirunamachandran.

ChemInform Abstract: FLUORESCENCE AND ABSORPTION SPECTRA OF ANTHRACENE CRYSTALS AT 4 K DOPED WITH 1‐ AND 2‐AMINOANTHRACENE, EFFECTS OF GUEST ORIENTATION

Chemischer InformationsdienstVolume 5, Issue 9 Physical Organic Chemistry ChemInform Abstract: FLUORESCENCE AND ABSORPTION SPECTRA OF ANTHRACENE CRYSTALS AT 4 K DOPED WITH 1- AND 2-AMINOANTHRACENE, EFFECTS OF GUEST ORIENTATION N. JAMES BRIDGE, N. JAMES BRIDGESearch for more papers by this authorDAVID VINCENT, DAVID VINCENTSearch for more papers by this author N. JAMES BRIDGE, N. JAMES BRIDGESearch for more papers by this authorDAVID VINCENT, DAVID VINCENTSearch for more papers by this author First published: March 5, 1974 https://doi.org/10.1002/chin.197409062AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume5, Issue9March 5, 1974 RelatedInformation