Donor-acceptor Charge Transfer Interactions Research Articles

A Halogen Bonding [2]Rotaxane Shuttle for Chloride-Selective Optical Sensing.

The first example of a [2]rotaxane shuttle capable of selective optical sensing of chloride anions over other halides is reported. The rotaxane was synthesised via a chloride ion template-directed cyclisation of an isophthalamide macrocycle around a multi-station axle containing peripheral naphthalene diimide (NDI) stations and a halogen bonding (XB) bis(iodotriazole) based station. Proton NMR studies indicate the macrocycle resides preferentially at the NDI stations in the free rotaxane, where it is stabilised by aromatic donor-acceptor charge transfer interactions between the axle NDI and macrocycle hydroquinone moieties. Addition of chloride ions in an aqueous-acetone solvent mixture induces macrocycle translocation to the XB anion binding station to facilitate the formation of convergent XB⋅⋅⋅Cl- and hydrogen bonding HB⋅⋅⋅Cl- interactions, which is accompanied by a reduction of the charge-transfer absorption band. Importantly, little to no optical response was induced by addition of bromide or iodide to the rotaxane, indicative of the size discriminative steric inaccessibility of the interlocked cavity to the larger halides, demonstrating the potential of using the mechanical bond effect as a potent strategy and tool in chloride-selective chemo-sensing applications in aqueous containing solvent environments.

DFT insight into Cd2+, Hg2+, Pb2+, Sn2+, As3+, Sb3+, and Cr3+ heavy metal ions adsorption onto surface of bowl-like B30 nanosheet

Contamination of water resources by heavymetal ions, is a drastic environmental concern. In this study, the interaction of Cd2+, Hg2+, Pb2+, Sn2+, As3+, Sb3+, and Cr3+ metal ions onto surface of the bowl-like B30 nanosheet was scrutinized based on density functional theory (DFT) calculations. Adsorption energy (Eads) values revealed that the As3+ interacted better with bowl-like B30 nanosheet in comparison to other metal ions, having adsorption energy values of −299.57 and −628.56 kcal mol−1in the gas phase and aqueous media, respectively. However, Hg2+, Pb2+, and Sn2+ metal ions physically adsorbed onto bowl-like B30 nanosheet in the gas phase because of their much less value of adsorption energy. The sign of adsorptionGibbs free energy change(ΔGads) and adsorption enthalpy change (ΔHads) values for all complexes was found to be negative in the gas phase and aqueous media, which indicated that the adsorption process is spontaneous and exothermic. Frontier molecular orbital (FMO) analysis exhibited a decrease in the HOMO-LUMO energy gap of studied complexes, boosting the electrical conductivity of these complexes. Natural bond orbital (NBO) analysis and charge decomposition analysis (CDA) revealed donor–acceptor charge transfer interactions in the complexes. The UV–vis results depicted that λmax was red-shifted during interactions of meal ions with bowl-like B30 nanosheet. Finally,quantum theoryof atoms in molecules (QTAIM) exhibited that the interaction between As3+ metal ion and the nanosheet is covalent in nature, while the other metal ions have predominantly electrostatic with partially covalent and non-covalent characters. The theoretical results of the study represented the feasibility of applying bowl-like B30 nanosheet to remove heavy metal ions, especially As3+ and providing information for experimental researchers to treat wastewaters.

Tuning the donor-acceptor interactions in phase-segregated block molecules.

The assembly of donor–acceptor molecules via charge transfer (CT) interactions gives rise to highly ordered nanomaterials with appealing electronic properties. Here, we present the synthesis and bulk co-assembly of pyrene (Pyr) and naphthalenediimide (NDI) functionalized oligodimethylsiloxanes (oDMS) of discrete length. We tune the donor–acceptor interactions by connecting the pyrene and NDI to the same oligomer, forming a heterotelechelic block molecule (NDI-oDMSPyr), and to two separate oligomers, giving Pyr and NDI homotelechelic block molecules (Pyr-oDMS and NDI-oDMS). Liquid crystalline materials are obtained for binary mixtures of Pyr-oDMS and NDI-oDMS, while crystallization of the CT dimers occurred for the heterotelechelic NDI-oDMS-Pyr block molecule. The synergy between crystallization and phase-segregation coupled with the discrete length of the oDMS units allows for perfect order and sharp interfaces between the insulating siloxane and CT layers composed of crystalline CT dimers. We were able to tune the lamellar domain spacing and donor–acceptor CT interactions by applying pressures up to 6 GPa on the material, making the system promising for soft-material nanotechnologies. These results demonstrate the importance of the molecular design to tune the CT interactions and stability of a CT material.

Charge-Transfer Interactions Stabilize G-Quadruplex-Forming Thrombin Binding Aptamers and Can Improve Their Anticoagulant Activity.

In the search for optimized thrombin binding aptamers (TBAs), we herein describe the synthesis of a library of TBA analogues obtained by end-functionalization with the electron-rich 1,5-dialkoxy naphthalene (DAN) and the electron-deficient 1,8,4,5-naphthalenetetra-carboxylic diimide (NDI) moieties. Indeed, when these G-rich oligonucleotides were folded into the peculiar TBA G-quadruplex (G4) structure, effective donor–acceptor charge transfer interactions between the DAN and NDI residues attached to the extremities of the sequence were induced, providing pseudo-cyclic structures. Alternatively, insertion of NDI groups at both extremities produced TBA analogues stabilized by π–π stacking interactions. All the doubly-modified TBAs were characterized by different biophysical techniques and compared with the analogues carrying only the DAN or NDI residue and unmodified TBA. These modified TBAs exhibited higher nuclease resistance, and their G4 structures were markedly stabilized, as evidenced by increased Tm values compared to TBA. These favorable properties were also associated with improved anticoagulant activity for one DAN/NDI-modified TBA, and for one NDI/NDI-modified TBA. Our results indicated that TBA pseudo-cyclic structuring by ad hoc designed end-functionalization represents an efficient approach to improve the aptamer features, while pre-organizing and stabilizing the G4 structure but allowing sufficient flexibility to the aptamer folding, which is necessary for optimal thrombin recognition.

Spectrophotometric studies on the charge transfer interactions between thiazolidine as a donor and three π-acceptors: p-Chloranil (CHL), DDQ and TCNQ

Constitute thiazolidine (TZD) loop heterogeneous systems have been explored extensively with a wide range of applications in physiological medical conditions such as diabetes and complications of diabetes, cancer, arthritis, inflammation, and infection of microbial and skin cancer. The electron donor-acceptor charge transfer interactions of thiazolidine with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), p-chloranil (CHL) and 7,7`,8,8`-tetracyanoquinodimethane (TCNQ) in methanol solvent have been associated a stable complexes with molar ratio 1:1 (acceptor: donor) and molecular formula [(TZD)(acceptor)]. The microanalytical (elemental analysis), UV–Vis. Spectra of both free reactants (donors & acceptors) and new charge transfer complexity, photometric titration, and infrared spectral analyses were employed to identify the donation sites in case of the formation charge-transfer interactions between donor and acceptor species. According to the modification of Benesi-Hildebrand equation, the physical spectroscopic data like association constant (K) and molar extinction coefficient (ε) were calculated.

Silver cluster (Ag6) decorated coronene as non-enzymatic sensor for glucose and H2O2

Silver-graphene quantum dots are promising electrochemical sensors due to their unique electronic properties. Herein, we report the comprehensive DFT study to explore the electronic properties of silver cluster (Ag6) decorated coronene as model for silver graphene quantum dots. The current study aims to investigate the sensing ability of silver-coronene complex for non-enzymatic electrochemical detection of glucose & H2O2. The stability of the complexes of analytes with silver decorated coronene is supported by their greater interaction energies (−36.7 to −44.9 kcal mol−1). NBO charge analysis and charge decomposition analysis (CDA) reveal donor-acceptor charge transfer interactions in the complexes. Frontier molecular orbital analysis illustrates that charge is transferred from analytes to silver decorated coronene during excitation from HOMO to LUMO. The Uv–visible results show that λmax is red shifted during interactions of analytes with silver decorated coronene. The NCI analysis illustrates the strong non-covalent (M … O) and unusual M … H–O interactions in the complexes. The precedent sensing performance of Ag6-coronene might be attributed to the synergistic effect of both silver clusters and coronene in the composite. The evaluated results validate the excellent sensing ability of silver-graphene quantum dots for the detection of glucose & H2O2. The outcome of the current study and its prospects will open the avenue for the rational development of smart sensors.

Template-assisted hydrogelation of a dynamic covalent polyviologen-based supramolecular architecture via donor-acceptor interactions

A novel polyviologen-based molecular architecture was developed via the step-growth polymerization of a hydroxyl-substituted aryl dihydrazide with a water soluble viologen-dialdehyde in water under acidic conditions. When polymerized in the presence of π-electron rich aromatic templates, the reaction mixture underwent hydrogelation. The templates were found to facilitate monomer-monomer as well as monomer-polymer preorganization during polymerization via donor-acceptor charge transfer interactions. Following polymerization, the templates effectively served as post-synthetic non-covalent cross linkers connecting the hydrogel network. The chemical structures of the polymers and molecular recognition between the reacting species were investigated in solution using 1H NMR, while donor-acceptor charge transfer interactions were investigated using UV-vis absorption spectroscopy. We also report the hydrochromic behavior of the templated and non-templated polymers. The surface morphology of the polymers was characterized using scanning electron microscopy, which revealed the formation of sheet-like structures. The new hydrogels developed in this work represents an interesting example of materials comprised of reversible dynamic covalent bonds and reversible non-covalent crosslinking interactions occurring between the electron-rich aryl templates and the electron-deficient bipyridinium units.

Single‐point Attack of Two H2O Molecules towards a Lewis Acid Site on the GaAl12 Clusters for Hydrogen Evolution

The hydrogen evolution reaction (HER) of water with metallic aluminum-based materials provides an important way to address the global energy challenge; however, fundamental mechanism and reaction dynamics governing the chemical and electronic properties remain a debated research topic. Here we further study the HER mechanisms for water splitting on typical 13-atoms clusters, Al12 Ga and Al13 , by first-principles DFT calculations. We noted that the doping of a Ga atom into the Al13 cluster could reduce the transition state barrier for H2 O dissociation on the metal cluster. Furthermore, it is interesting that the second water molecule prefers to adsorb on the same metal site giving rise to both thermodynamically and kinetically favorable reaction pathways. Based on the well-established complementary active sites (CAS) mechanism for metal cluster reactivity, we provide insights into the reaction dynamics of such metal clusters with two water molecules, which also sheds light on the Eley-Rideal and Langmuir-Hinshelwood mechanisms in surface science. Natural bond orbitals (NBO) analysis was conducted to evaluate the donor-acceptor charge-transfer interactions between the cluster and the nucleophilic reagent. These results gain a better understanding of the mechanism for water reacting with aluminum-based materials.

Quantum Tunneling Tautomer of N,N-Dimethyl-p-toluidine Dehydrogenates Identified by Deep-UV Laser Ionization Mass Spectroscopy.

Utilizing customized deep-ultraviolet laser ionization mass spectroscopy, here we report a finding of remarkable dehydrogenation product of N,N-dimethyl-p-toluidine (DMT). The DMT dehydrogenates find comparable mass abundance with the DMT molecule ions showing decent stability at the loss of one electron and one H atom from the DMT molecule. First-principles calculation reveals that the dehydrogenation most readily occurs at the N-connected methyl group. Furthermore, at the removal of a hydrogen atom, a neighboring hydrogen atom on the other methyl come close and interact with the dehydrogenated methylene group, pertaining to C–H···C weak interactions which give rises to a resonant structure (C···H–C) on a basis of hydrogen atom quantum tunneling effect. The quantum tunneling tautomer of DMT dehydrogenates displays reversible donor–acceptor charge-transfer interactions as demonstrated by natural bonding orbital analysis and vibrational spectroscopy. It is worth noting that the novel dehydrogenation product was also observed for another small organic molecule o-phenylenediamine, which bears two neighboring amino groups and the subsequent dehydrogenation product pertains to resonant structures of N–H···N and N···H–N. The deep ultraviolet laser not only produces fragmentation-free mass spectra for such small organic molecules but also tailors the interesting quantum tunneling tautomer from such specific molecules.

Atropisomerism about aryl-Csp(3) bonds: the electronic and steric influence of ortho-substituents on conformational exchange in cannabidiol and linderatin derivatives.

Terpenylation reactions of substituted phenols were used to prepare cannabidiol and linderatin derivatives, and their structure and conformational behavior in solution were investigated by NMR and, for some representative examples, by DFT. VT-NMR spectra and DFT calculations were used to determine the activation energies of the conformational change arising from restricted rotation about the aryl-Csp(3) bond that lead to two unequally populated rotameric epimers. The NBO calculation was applied to explain the electronic stabilization of one conformer over another by donor-acceptor charge transfer interactions. Conformational control arises from a combination of stereoelectronic and steric effects between substituents in close contact with each other on the two rings of the endocyclic epoxide atropisomers. This study represents the first exploration of the stereoelectronic origins of atropisomerism around C(sp(2))-C(sp(3)) single bonds through theoretical calculations.

Controlling charge separation in a novel donor–acceptor metal–organic framework via redox modulation

Donor–acceptor charge transfer interactions in a tetrathiafulvalene–naphthalene diimide-based metal–organic framework (MOF) are interrogated using a complementary suite of solid state spectroscopic, electrochemical and spectroelectrochemical methods along with computational calculations.

Polymer–water interactions. Origin of perturbed infrared intensities of water in polymeric systems

We explore the possible reasons for the huge infrared intensity perturbations of water molecules sorbed onto a variety of polymer surfaces. We demonstrate that strong polymer–water interactions, not always obvious from qualitative approaches to examination of the water vibrational spectra, are probably responsible for such effects. The deviations from Beer’s law for water adsorption is semi-quantitatively correlated with the level of water uptake (i.e. water activity in the polymer). This clearly demonstrates the dependence on water–polymer proximity and intermolecular interaction strength, to the extent that donor–acceptor charge transfer interactions may well control this interesting, and potentially useful, phenomenon.

Nonlinear Optical Materials Based on Benzobisthiazole. Electronic Structure/Molecular Architecture/Polarizability/Hyperpolarizability Relationships Derived from π-Electron Theory

ABSTRACTFactors contributing to the polarizability (αij) and frequencydoubling hyperpolarizability (βijk) of 2-(p-dimethylaminophenyl)-6-(pnitrophenyl) benzo(l,2-d:4,5-d′ )blsthiazole (DNBT) are analyzed via perturbation theory and the PPP-SCF-MECI π-electron model Hamiltonian. While the observable part of β (βvec) is clearly identifiable with a small number of charge transfer excitations along the molecular dipole direction, a (and by inference, the second-order hyperpolarizability γ) is more closely related to the overall size (volume) of the π-electron cloud. As a consequence, βvec is far more sensitive to molecular distortions which affect donor-acceptor charge transfer interactions than is π. The more sensitive frequency dependence of βvec can be understood in terms of the three-photon character of this nonlinearity.

Molecular complexes. Part XXIII. Crystal and molecular structures of α-naphthol–1,2,4,5-tetracyanobenzene and β-naphthol–1,2,4,5-tetracyanobenzene

The crystal and molecular structures of the 1 : 1 complexes of α-naphthol and 1,2,4,5-tetracyanobenzene (I) and β-naphthol and 1,2,4,5-tetracyanobenzene (II) have been determined by Fourier methods from diffractometer data and refined by least-squares to R 0.043 for 523 reflections (I), and R 0.104 for 651 reflections (II). Both are monoclinic, space group C2/m with Z= 2 in unit cells of dimensions: (I), a= 9.250(5), b= 13.059(7), c= 6.791(4)A, β= 108.3(1)°; (II), a= 9.578(1), b= 12.754(3), c= 6.798(4)A, β= 108.13(2). The dimensions of the component molecules have been corrected for rigid-body thermal motion and are in agreement with those from previous work. The mode of donor–acceptor overlap of the molecules in the alternate plane-to-plane stacks parallel to the c axes of the crystals gives near-maximisation of the donor–acceptor charge-transfer interactions. The naphthol molecules in both structures are disordered.