Molecular Charge Transfer Research Articles

Molecular structure, vibrational analysis (IR and Raman) and quantum chemical investigations of 1-aminoisoquinoline

Quantum chemical calculations of energy and geometrical parameters of 1-aminoisoquinoline [1-AIQ] were carried out by using DFT/B3LYP method using 6-311G (d,p), 6-311G++(d,p) and cc-pVTZ basis sets. The vibrational wavenumbers were computed for the energetically most stable, optimized geometry. The vibrational assignments were performed on the basis of potential energy distribution (PED) using VEDA program. The NBO analysis was done to investigate the intra molecular charge transfer of the molecule. The frontier molecular orbital (FMO) analysis was carried out and the chemical reactivity descriptors of the molecule were studied. The Mulliken charge analysis, molecular electrostatic potential (MEP), HOMO-LUMO energy gap and the related properties were also investigated at B3LYP level. The absorption spectrum of the molecule was studied from UV–Visible analysis by using time-dependent density functional theory (TD-DFT). Fourier Transform Infrared spectrum (FT-IR) and Raman spectrum of 1-AIQ compound were analyzed and recorded in the range 4000–400 cm−1 and 3500-100 cm−1 respectively. The experimentally determined wavenumbers were compared with those calculated theoretically and they complement each other.

Molecular structure, vibrational spectroscopic analysis (IR & Raman), HOMO-LUMO and NBO analysis of anti-cancer drug sunitinib using DFT method

Oxindole and its derivatives have wide applications in different industries such as in synthetic & natural fibers, dyes for hair and plastic materials in addition to their biological importance. In the present study, one of the oxindole derivatives, N-(2-diethylaminoethyl)-5-[(Z)-(5-fluoro-2-oxo-1H-indol-3-ylidene)methyl]-2,4-dimethyl-1H-pyrrole-3-carboxamide (Sunitinib), which is used as an anti-cancer drug, was investigated in terms of structural, vibrational spectroscopic and theoretical analysis. The calculations have been performed for gaseous, aqueous and DMSO phases, respectively. Potential Energy Surface (PES) scan has been carrried out to obtain the most stable structures of all the phases of the title molecule using B3LYP/6-31G(d,p) level and the geometrical variations among them are discussed. The solvent effect for Sunitinib in aqueous and DMSO phases have been performed by means of the self-consistent recognition reaction field (SCRF) method as implemented in the integral equation formalism polarized continuum model (IEFPCM). On the other hand, NBO analysis has been carried out to understand probable hydrogen bonding sites and charge transfers. Additionally, the HOMO and the LUMO energies are calculated using B3LYP/6-31G(d,p) to determine the intra molecular charge transfers (ICT) within the molecule and the kinetic stabilities for each phases. The molecular electrostatic potential surface (MESP) has been plotted over the optimized structure to estimate the reactive sites of electrophilic and nucleophilic attacks regarding Sunitinib molecule. The potential energy distribution (PED) has been calculated using VEDA4 program and vibrational assignments of the experimental spectra (IR & Raman) have been elucidated by means of the calculated vibrational spectra. The observed vibrational spectra of Sunitinib is compared with the calculated spectra obtained by using B3LYP functional both with 6-31G(d,p) and 6-311++G(d,p) basis sets. Theoretical results indicate that the best correlation with experimental data is obtained with B3LYP/6-311++G(d,p) method.

Responsive mechanism of three novel hypochlorous acid fluorescent probes and solvent effect on their sensing performance**Project supported by the National Natural Science Foundation of China (Grant Nos. 11374195 and 11404193) and the Taishan Scholar Program of Shandong Province, China.

Optical properties and responsive mechanisms of three newly synthesized fluorescent probes for hypochlorous acid (HOCl) are investigated by employing time-dependent density functional theory. The computational results show that the absorption and emission properties of these probes change obviously when they react with hypochlorous acid. It is found that the probe FHZ has the best performance according to the probing behavior. Moreover, the responsive mechanisms of the probes are studied by analyzing the distributions of molecular orbitals and charge transfer, which are shown as the photon-induced electron transfer (PET) for FHZ and the intramolecular charge transfer (ICT) for the other two probes. Specially, solvent effect on optical properties of the probe FHZ before and after reaction is studied within the polarizable continuum model (PCM). It is shown that performance of the probe depends crucially on the solvent polarity. Our computational results agree well with the experimental measurement, and provide information for design of efficient two-photon fluorescent probes.

Low-Dimensional Carbon Allotropes: Ground- and Excited-State Charge Transfer with NIR-Absorbing Heptamethine Cyanine

Summary At the focal point of our studies are mutual interactions between an anionic heptamethine cyanine and individualized single-walled carbon nanotubes (SWCNTs) or exfoliated nanographene (NG). Here, we report the distinct near-infrared absorption of the heptamethine cyanine, which assists in visualizing the electronic interactions in the ground state with ease and precision. In statistical Raman assays, we conclude from downshifted 2D- and G-modes for SWCNTs, as well as upshifted 2D- and downshifted G-modes for NG, that these electronic interactions result in stable n-doping of SWCNTs and NG. Key to this shift of charge density is the electron-donating character of the heptamethine cyanine. In the excited state, a complete but metastable transfer of charges is accompanied by a radical-ion-pair state that lives for several nanoseconds. Such a time domain has not yet been realized, for example, in NG to date.

Unusual solvent effect of molecular charge transfer complexes: Stacking/non-stacking interaction revealed by characterization of structure and photophysical aspects

The molecular charge transfer complexes using 9-methyl anthracene (9MA) and pyrene as donors and pyromellitic diimide (PMDI) as acceptor have been characterized by crystal structure analysis and photophysical studies. A π-π stacking interaction is observed in case of the 1:1 PMDI-Pyrene CT complex whereas the 1:1 PMDI-9MA CT complex exhibits selective stacking structure of the acceptor and donor in an interlock manner. The optimized structures from DFT calculations of PMDI-9MA and PMDI-Pyrene CT complexes in gas phase support the results. The photophysical studies of these complexes have been compared with the CT complexes of PMDA with four donors Naphthalene, Anthracene, Methyl Anthracene and Pyrene and the CT complexes of NTCDA with Methyl Anthracene and Pyrene. All the PMDA CT complexes exhibit blue shift of the charge transfer absorption and the corresponding emission band with increasing polarity of the solvents. This unusual solvent effect has been ascribed to specific interaction of the acceptor with the solvent. The red shift of the CT band in the solid state for the complexes compared to that observed in solvents support the contention of specific interaction. The binding constants for all the CT complexes are found to be of the order of 103 and the interplanar spacing of the stacked complexes is found to be around 3.3Å. Time resolved emissions of all the complexes reveal two different conformations in solution. The average lifetime of fluorescence in transparent KBr pellet is observed to be longer than that in solution. The structural properties, the spectral data and the geometry of the complexes in the excited states evaluated by TDDFT and DFT methods match well with the experimental results. These studies will help understand π-π interaction in supramolecular systems and in various biological interactions.

Crystal structure, vibrational spectra and DFT studies of hydrogen bonded 1,2,4–triazolium hydrogenselenate

The new hydrogen bonded molecular complex 1,2,4–triazolium hydrogenselenate (THS) is prepared by the reaction of 1H–1,2,4–triazole and selenic acid. This complex is stabilised by N–H⋯O and C–H⋯O hydrogen bonding and electrostatic attractive forces between 1H and 1,2,4–triazolium cations and hydrogen selenate anions. The XRD studies revealed that intermolecular proton transfer occur from selenic acid to 1H–1,2,4–triazole molecule, results in the formation of 1,2,4–triazolium hydrogenselenate which contains 1,2,4–triazolium cations and hydrogenselenate anions. The molecular structure of THS crystal has also been optimised by using Density Functional Theory (DFT) using B3LYP/cc–pVTZ and B3LYP/6–311++G** methods in order to find the whole characteristics of the molecular complex. The theoretical structural parameters such as bond length, bond angle and dihedral angle determined by DFT methods are well agreed with the XRD parameters. The atomic charges and thermodynamic properties are also calculated and analysed. The energies of frontier molecular orbitals HOMO, LUMO, HOMO–1, LUMO+1 and LUMO–HUMO energy gap are calculated to understand the kinetic stability and chemical reactivity of the molecular complex. The natural bond orbital analysis (NBO) has been performed in order to study the intramolecular bonding interactions and delocalisation of electrons. These intra molecular charge transfer may induce biological activities such as antimicrobials, antiinflammatory, antifungal etc. The complete vibrational assignments of THS have been performed by using FT–IR and FT–Raman spectra.

Dye-Sensitized Molecular Charge Transfer Complexes: Magnetic and Conduction Properties in the Photoexcited States of Ni(dmit)2 Salts Containing Photosensitive Dyes

Photosensitive dyes often induce charge transfer (CT) between adjacent chemical species and themselves under irradiation of appropriate wavelengths. Because of the reversibility and selectivity of such CT, it is considered to be interesting to utilize such dyes as optically controllable trigger components for conduction and magnetism in the photoexcited states of organic materials. Based on this idea, such a type of new salts, i.e., γ- and δ-DiCC[Ni(dmit)2] in addition to DiCC2[Ni(dmit)2]3 have been prepared, characterized and their physical and structural properties have been examined both under dark and irradiated conditions (dmit2− = 1,3-dithiole-2-thione-4,5-dithiolate, DiCC+ = 3,3′-Dihexyloxacarbocyanine monocation). Among them, under UV (254–450 nm) irradiation, δ-DiCC[Ni(dmit)2] exhibited photoconductivity being six times as high as its dark conductivity at room temperature. The electron spin resonance (ESR) spectra have demonstrated that there are photoexcited spins on both DiCC and [Ni(dmit)2] species as a result of the CT transition between them, serving as localized spins (DiCC) and carriers ([Ni(dmit)2]), respectively. The results obtained in this work have indicated that the strategy mentioned above is effective in developing organic photoresponsive semiconductors with paramagnetism.

Molecular Arrangement and Charge Transfer in C60/Graphene Heterostructures.

Charge transfer at the interface between dissimilar materials is at the heart of electronics and photovoltaics. Here we study the molecular orientation, electronic structure, and local charge transfer at the interface region of C60 deposited on graphene, with and without supporting substrates such as hexagonal boron nitride. We employ ab initio density functional theory with van der Waals interactions and experimentally characterize interface devices using high-resolution transmission electron microscopy and electronic transport. Charge transfer between C60 and the graphene is found to be sensitive to the nature of the underlying supporting substrate and to the crystallinity and local orientation of the C60. Even at room temperature, C60 molecules interfaced to graphene are orientationally locked into position. High electron and hole mobilities are preserved in graphene with crystalline C60 overlayers, which has ramifications for organic high-mobility field-effect devices.

Defect-Mediated Molecular Interaction and Charge Transfer in Graphene Mesh-Glucose Sensors.

We report the role of defects in enzymatic graphene field-effect transistor sensors by introducing engineered defects in graphene channels. Compared with conventional graphene sensors (Gr sensors), graphene mesh sensors (GM sensors), with an array of circular holes, initially exhibited a higher irreversible response to glucose, involving strong chemisorption to edge defects. However, after immobilization of glucose oxidase, the irreversibility of the responses was substantially diminished, without any reduction in the sensitivity of the GM sensors (i.e., -0.53 mV/mM for the GM sensor vs -0.37 mV/mM for Gr sensor). Furthermore, multiple cycle operation led to rapid sensing and improved the reversibility of GM sensors. In addition, control tests with sensors containing a linker showed that sensitivity was increased in Gr sensors but decreased in GM sensors. Our findings indicate that edge defects can be used to replace linkers for immobilization of glucose oxidase and improve charge transfer across glucose oxidase-graphene interfaces.

Characteristics of the molecular electron density, delocalization effect and hydrogen bonding interaction of nitroxoline

The density functional theoretical (DFT) calculations have been carried out at the B3LYP/6-311G(d,p) level of theory for nitroxoline monomer and dimer molecule. The dimer molecule formed between two nitroxoline subunits has the largest stability, and is held together by two OH⋯N hydrogen bonds. Stability of the molecule arising from hyperconjugative interaction and intra/inter molecular charge transfer has been analyzed using natural bond orbital (NBO) analysis. The topological analysis of electron localization function (ELF) provides effect of delocalization. Quantum theory of atoms in molecule (QTAIM) has been applied to gain deep understanding to the existence of intra- and inter-molecular interaction.

Charge-transfer interaction of 4-(2-pyridylazo)resorcinol with nitroaromatics: Insights from experimental and theoretical results

Molecular charge-transfer (CT) complexation of the donor 4-(2-pyridylazo)resorcinol (1P) with selected nitroaromatic acceptors as like, 2,4-DNP, 3,5-DNSA, 3,5-DNBA, and PA have been studied in methanol at room temperature. Among the selected nitroaromatics we have isolated 1P-3,5-DNSA and 1P-PA complexes and characterized them using FT-IR, 1H NMR studies, and elemental analysis. UV–vis studies revealed that upon interaction of 1P with nitroaromatics a charge-transfer band arises which has remarkably different absorption region than the donor and the acceptor. Titrimetric studies of the ground state show the presence of one isosbestic point which also indicates the strong proton-transfer equilibrium between the molecules. Fluorescence quenching studies were also carried out to find out the Stern-Volmer binding constant (KSV) and the quenching efficiency. FT-IR and 1H NMR studies indicate that the complexation is due to the acute H-bonding interactions. Theoretical calculations (DFT) also propose the formation of the H-bonded adducts.

Effects of energy correlations and superexchange on charge transport and exciton formation in amorphous molecular semiconductors: An ab initio study

In this study, we investigate on the basis of ab initio calculations how the morphology, molecular on-site energies, reorganization energies, and charge transfer integral distribution affect the hopping charge transport and the exciton formation process in disordered organic semiconductors. We focus on three materials applied frequently in organic light-emitting diodes: $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{NPD}$, TCTA, and Spiro-DPVBi. Spatially correlated disorder and, more importantly, superexchange contributions to the transfer integrals, are found to give rise to a significant increase of the electric field dependence of the electron and hole mobility. Furthermore, a material-specific correlation is found between the HOMO and LUMO energy on each specific molecular site. For $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{NPD}$ and TCTA, we find a positive correlation between the HOMO and LUMO energies, dominated by a Coulombic contribution to the energies. In contrast, Spiro-DPVBi shows a negative correlation, dominated by a conformational contribution. The size and sign of this correlation have a strong influence on the exciton formation rate.

Na-ion batteries based on the inorganic BN nanocluster anodes: DFT studies

It has been recently indicated that the Li-ion batteries may be replaced by Na-ion batteries because of their low safety, high cost, and low-temperature performance, and lack of the Li mineral reserves. Here, using density functional theory calculations, we studied the potential application of B12N12 nanoclusters as anode in Na-ion batteries. Our calculations indicate that the adsorption energy of Na+ and Na are about −23.4 and −1.4kcal/mol, respectively, and the pristine BN cage to improve suffers from a low cell voltage (∼0.92V) as an anode in Na-ion batteries. We presented a strategy to increase the cell voltage and performance of Na-ion batteries. We showed that encapsulation of different halides (X=F−, Cl−, or Br−) into BN cage significantly increases the cell voltage. By increasing the atomic number of X, the Gibbs free energy change of cell becomes more negative and the cell voltage is increased up to 3.93V. The results are discussed based on the structural, energetic, frontier molecular orbital, charge transfer and electronic properties and compared with the performance of other nanostructured anodes.

Synthesis, growth and characterization of o-phenylinediaminium benzilate: An SHG material with high laser damage threshold for NLO applications

An organic molecular charge transfer complex salt, o-phenylenediaminium benzilate was synthesized and single crystals grown by slow solvent evaporation solution growth technique in methanol at ambient temperature. The grown crystal was subjected to Single crystal XRD analysis to establish the molecular structure. The molecular structure was further confirmed by 1H and 13C NMR spectral studies. The formation of the charge transfer complex salt was confirmed by UV–VIS spectroscopic technique. To identify the optical transmittance window and lower wavelength cut-off, the crystal was subjected to UV–Vis–NIR transmission spectral studies. The presence of various functional groups in the salt crystal was confirmed by FT-IR spectroscopic technique. Photoluminescence study was carried out to explore its efficiency towards device fabrications. The TG and DTA thermal analyses were simultaneously carried out to establish the thermal stability of the crystal. The dielectric studies of the grown crystal were executed at different temperatures as a function of frequency to investigate its electrical properties. The SHG efficiency of the crystal was determined using the modified Kurtz and Perry powder technique and its value was found to be 1.98 times that of the KDP crystal. Laser damage threshold value was measured using Nd:YAG laser. The mechanical stability of the title crystal was established employing Vickers micro hardness tester.

Donor–acceptor single cocrystal of coronene and perylene diimide: molecular self-assembly and charge-transfer photoluminescence

Organic semiconductor molecules, coronene and perylene diimide, form an alternate stacked cocrystal due to the strong donor–acceptor charge transfer interaction.

Spatial quenching of a molecular charge-transfer process in a quantum fluid: the Csx–C60reaction in superfluid helium nanodroplets

A recent experimental study [Renzler et al., J. Chem. Phys., 2016, 145, 181101] on superfluid helium nanodroplets reported different reactivities for Cs atoms and Cs2 dimers with C60 fullerenes inside helium droplets. Alkali metal atoms and clusters are heliophobic, therefore typically residing on the droplet surface, while fullerenes are fully immersed into the droplet. In this theoretical study, which combines standard methods of computational chemistry with orbital-free helium density functional theory, we show that the experimental findings can be interpreted in the light of a quenched electron-transfer reaction between the fullerene and the alkali dopant, which is additionally hindered by a reaction barrier stemming from the necessary extrusion of helium upon approach of the two reactants.

EXPERIMENTAL AND THEORETICAL INVESTIGATION OF MOLECULAR STRUCTURE AND CHARGE TRANSFER WITHIN SOME 8-HYDROXYQUINOLINE DERIVATIVES

A serie of novel 8-hydroxyquinoline derivatives: 5-HHQ, 5-MHQ, 5-EHQ and 5-PHQ were synthesized and characterized by means of IR, 1H and 13C NMR spectroscopic analysis. The crystal structures of 5-EHQ and 5-PHQ were solved by X-ray diffraction measurements on single crystal, the two others on powder samples. The UV–Visible spectra of molecules were performed in acetonitrile and ethanol. Density Functional Theory (DFT) and Hartree Fock (HF) methods have been used to determine its optimized geometrical parameters. Theoretical calculations such as HOMO-LUMO energies in fundamental state, in acetonitrile and ethanol, electronic dipole moments and atomic charges distribution were carried out for the title molecules using DFT (B3LYP) method at 6-311G (d, p) set. The results give us some explanation on the molecular structures, the intra charge transfer, relationships between the number of carbons connected to 5-hydroxymethyl-8-hydroxyquinoline and the bioactivity of selected derivatives.

Self-assembly of F16ZnPc thin films and F16ZnPc-ZnPc heterostructures on deactivated Si surfaces studied by scanning tunneling microscopy.

Using scanning tunneling microscopy, we show that hexadecafluorinated zinc phthalocyanine (F16ZnPc) molecules form two morphologically different self-assembled structures that both display point-on-line coincident epitaxial registration with the deactivated Si(111)-B 3×3 surface. The packing motif in these structures suggests that fluorination of conjugated organic molecules can lead to stronger molecule-substrate interaction, π-π intermolecular interaction, and side-to-side intermolecular repulsion. The delicate balance and interplay between these interactions determine the self-assembly behavior of fluorinated molecules. Furthermore, we demonstrate the formation of vertically and laterally stacked F16ZnPc-ZnPc heterojunctions, allowing for future spectroscopy investigation of molecular electronic structures and charge transfer behavior at organic-organic hetero-interfaces.

The particle-hole map: Formal derivation and numerical implementation.

The particle-hole map (PHM) is a tool to visualize electronic excitations, based on representations in a canonical orbital transition space. Introduced as an alternative to the transition density matrix, the PHM has a simple probabilistic interpretation, indicating the origins and destinations of electrons and holes and, hence, the roles of different functional units of molecules during an excitation. We present a formal derivation of the PHM, starting from the particle-hole transition density matrix and projecting onto a set of single-particle orbitals. We implement the PHM using atom-centered localized basis sets and discuss the example of the molecular charge-transfer complex C2H4-C2F4.

Electrochemical Performance of La1.5Sr0.5Ni1-xFexO4+δ Cathode for IT-SOFCs

La1.5Sr0.5Ni1-xFexO4+δ (LSNF, x=0, 0.3, 0.5) series materials are synthesized as potential cathode materials for intermediate-temperature solid fuel cells by an EDTA-citrate complexation process. The effects of Fe substitution for Ni on the structure, transport property and electrochemical performances are investigated. X-ray diffraction shows that all samples with Fe-doping are identified as single phase materials with a tetragonal I4/mmm space group. Fe-doping decreases electrical conductivity of La1.5Sr0.5Ni1-xFexO4+δ. The study of symmetrical cells with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) as an electrolyte shows a decreasing tendency of polarization resistance (Rp) of La1.5Sr0.5Ni1-xFexO4+δ with increasing Fe content. The impedance data at different oxygen partial pressures reveal that the electrode reaction is controlled by the molecular oxygen dissociation and charge transfer processes. The substitution of Fe improves the electrode kinetics and enhances the electrochemical performance of LSNF electrode significantly. The LSGM electrolyte (400μm) supported single cell with La1.5Sr0.5Ni0.5Fe0.5O4+δ as cathode and Ni-Gd0.1Ce0.9O2-δ as anode delivers relatively high power density of 282mWcm−2 at 800°C.