Noncovalent π⋅⋅⋅π interaction between graphene and aromatic molecule: structure, energy, and nature

One-step simultaneous liquid phase exfoliation-induced chirality in graphene and their chirality-mediated microRNA delivery

Graphene (G) has established itself as an exciting prospect for a broad range of applications owing to its remarkable properties. Recent innovations in chiral nanosystems have led to sensors, drug delivery, catalysis, etc. owing to the stereospecific interactions between various nanosystems and enantiomers. As the molecular structure of G itself is achiral introducing chirality in G by simple attachment of a functional group (a chiral ligand) on the G nanosheet may result in more diverse applications. Herein, we demonstrate direct liquid phase exfoliation and chiral induction in G nanosheets abbreviated as l-graphene and d-graphene in the presence of chiral l-tyrosine and d-tyrosine and by applying high-temperature sonication. The obtained exfoliated nanosheets demonstrated stable chirality confirmed by circular dichroism. Fourier transform infrared (FTIR) spectra, Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and differential scanning calorimetry (DSC) showed functional, structural, morphological, surface, and thermal characteristics of l-graphene and d-graphene. The hemo-compatibility of these chiral graphenes was evaluated for the very first time utilizing human red blood cells. Lastly, for the very first time, an attempt was made to explore enantiomeric binding between chiral l-graphene and d-graphene with microRNA (miR-205) and their possibility towards chirality-mediated gene delivery in prostate cancerous cells.

Hazards of polycyclic aromatic hydrocarbons: a review on occurrence, detection, and role of green nanomaterials on the removal of PAH from the water environment

Organic pollutant contamination in the environment is a serious and dangerous issue, especially for developing countries. Among all organic pollutants, polycyclic aromatic hydrocarbons (PAHs) are the more frequently discovered ones in the environment. PAH contamination is caused chiefly by anthropogenic sources, such as the disposal of residential and industrial waste and automobile air emissions. They are gaining interest due to their environmental persistence, toxicity, and probable bioaccumulation. The existence of PAHs may result in damage to the environment and living things, and there is widespread concern about the acute and chronic threats posed by the release of these contaminants. The detection and elimination of PAHs from wastewater have been the focus of numerous technological developments during recent decades. The development of sensitive and economical monitoring systems for detecting these substances has attracted a lot of scientific attention. Using several nanomaterials and nanocomposites is a promising treatment option for the identification and elimination of PAHs in aquatic ecosystems. This review elaborated on the sources of origin, pathogenicity, and widespread occurrence of PAHs. In addition, the paper highlighted the use of nanomaterial-based sensors in detecting PAHs from contaminated sites and nanomaterial-based absorbents in PAH elimination from wastewater. This review also addresses the development of Graphene and Biofunctionalized nanomaterials for the elimination of PAHs from the contaminated sites.

Cu2+@metal-organic framework-derived amphiphilic sandwich catalysts for enhanced hydrogenation selectivity of ketenes at the oil-water interface

Selective catalysis has always been an essential process for manufacturing various fine chemicals, such as food additives, pharmaceuticals and perfumes. Practically, pure target products are difficult to obtain even after complex purification procedures during industrial production. The development of a cost-effective, highly chemoselective and long-life catalyst may be an attractive solution, but such a catalyst is elusive. Herein, a novel class of amphiphilic N-doped carbon (NC), featuring graphitic carbon (GC) and highly dispersed Cu@Co NPs, was fabricated via simple calcination of a Cu2+-doped bimetallic metal-organic framework (MOF) precusor directly. Compared with monometallic Co@GC/NC, the side reaction of CO bond hydrogenation is obviously restrained, and thus, pure target product can be systematically obtained by Cu@Co@GC/NC, highlighting the high selectivity of Cu. More importantly, an amphiphilic characteristic in Cu@Co@GC/NC is a significant knob to integrate organic substrates with water very well. This amphiphilic material shows great potential as a field-deployable pathway for dispersible metal catalysts in organic systems.

Colloidal stability of graphene in aqueous medium: a theoretical approach through molecular dynamics

CONTEXT

Graphene has been used as reinforcement of polymeric nanocomposites to increase mechanical and electrical properties. Recently, graphene suspensions have been used for the development of nanofluids in automotive applications, where improvements in convection heat transfer coefficients and pressure drops have been reported. However, dispersions of graphene sheets in a polymeric matrix as well as in a solvent medium are difficult to achieve; that is because Van der Waals, [Formula: see text] and Coulombic interactions cause agglomerations. Surface chemical modifications have been considered as viable options to improve the graphene integration. In this work, we studied the colloidal stability of aqueous solutions of graphene sheets functionalized with (i) carboxylic groups, (ii) 3-amino-propyl tri-ethoxy silane (amphiphilic behavior), (iii) graphene oxide, and (iv) pristine graphene. Results show that the lower sedimentation velocity corresponds to the graphene functionalized with carboxylic groups, which presents the higher colloidal stability. However, the amphiphilic group enhances the interaction energy between graphene and the solvent; we believe that there is a threshold percentage of functionalization that improves the colloidal stability of graphene.

METHOD

Transport properties of graphene solutions were estimated by using Non-Equilibrium Molecular Dynamics simulations to generate Poiseuille flow in an NVT ensemble. Simulations were developed in the LAMMPS code. The COMPASS Force Field was used for the graphene systems and the TIP3P for the water molecules. Bonds and angles of hydrogen atoms were kept rigid by using the shake algorithm. The molecular models were built through MedeA and visualized with the Ovito software.

Carbon nanotube-decorated hierarchical porous nickel/carbon hybrid derived from nickel-based metal-organic framework for enhanced methyl blue adsorption

This work reports the incorporation of coordinated water into Ni-BTC nanorods (Ni-BTC-O) which induces their structural transformation to Ni-BTC nanofibres (Ni-BTC-F). The carbonization of the Ni-BTC nanofibres at 600 °C results in the formation of carbon nanotube (CNT)-decorated hierarchical porous nickel/carbon hybrid (labelled as Ni/C-600) with enlarged pores. In contrast, the Ni/C hybrid obtained from the carbonization of the original (unmodified) Ni-BTC nanorods (Ni-BTC-O) at 600 °C (labelled as Ni-BTC-O-600) exhibits smaller pore size and does not show the formation of CNTs. The Ni/C-600 hybrid derived from Ni-BTC-F shows a very high adsorption capacity of 686.8 mg g^-1 toward methyl blue (MB) dye. This is approximately 4.8 times higher than the adsorption capacity of Ni-BTC-O-600 (144.1 mg g^-1). The higher adsorption performance of Ni/C-600 relative to Ni-BTC-O-600 can be attributed to its larger pore volume, hierarchical porosity, and additional adsorption sites provided by the CNTs. In addition, the Ni/C-600 hybrid can maintain 90% of its adsorption capacity after 5 consecutive cycles, demonstrating its potential as an efficient and recyclable adsorbent for MB dye.

Graphene Modification by Curcuminoids as an Effective Method to Improve the Dispersion and Stability of PVC/Graphene Nanocomposites

A large amount of graphene-related research is its use as a filler for polymer composites, including thin nanocomposite films. However, its use is limited by the need for large-scale methods to obtain high-quality filler, as well as its poor dispersion in the polymer matrix. This work presents polymer thin-film composites based on poly(vinyl chloride) (PVC) and graphene, whose surfaces were modified by curcuminoids. TGA, UV-vis, Raman spectroscopy, XPS, TEM, and SEM methods have confirmed the effectiveness of the graphene modification due to π-π interactions. The dispersion of graphene in the PVC solution was investigated by the turbidimetric method. SEM, AFM, and Raman spectroscopy methods evaluated the thin-film composite's structure. The research showed significant improvements in terms of graphene's dispersion (in solutions and PVC composites) following the application of curcuminoids. The best results were obtained for materials modified with compounds obtained from the extraction of the rhizome of Curcuma longa L. Modification of the graphene's surface with these compounds also increased the thermal and chemical stability of PVC/graphene nanocomposites.

Bifurcated halogen bonds in the crystal structure of 2,2′-bi(1,8-naphthyridine)—1,4-diiodotetrafluorobenzene (1/1), C22H10F4I2N4

C22H10F4I2N4, monoclinic, P21/c (no. 14), a = 9.7940(3) Å, b = 5.34970(10) Å, c = 20.5119(5) Å, β = 101.673(3)°, V = 1052.49(5) Å3, Z = 2, R gt (F) = 0.0222, wR ref (F 2) = 0.0505, T = 293(2) K.

Review of research of nanocomposites based on graphene quantum dots

Graphene quantum dots (GQDs) belong to the vast and versatile family of carbon nanomaterials. Their unique position amongst versatile carbon nanoparticles (NPs) originates from the properties of quantum confinement and edge effects. GQDs are similar to conventional semiconductor QDs due to their tunable band gaps and high photoluminescence activity. However, GQDs have superior characteristics due to their excellent biocompatibility, low toxicity, good water dispersibility, large optical absorptivity, high fluorescence activity and photostability. These properties have generated significant interest in GQDs applications in various fields: nanosensor fabrication, drug delivery, photocatalysis, photovoltaics, and photodynamic therapy. Numerous GQD-based nanocomposites/nanohybrides have been synthesized and/or studied computationally. This review focuses on recent computational studies of various GQD-based nanocomposites/nanohybrides and systems which can be related to them.

A Comprehensive DFT Investigation of the Adsorption of Polycyclic Aromatic Hydrocarbons onto Graphene

To better understand graphene and its interactions with polycyclic aromatic hydrocarbons (PAHs), density-functional-theory (DFT) computations were used. Adsorption energy is likely to rise with the number of aromatic rings in the adsorbates. The DFT results revealed that the distance between the PAH molecules adsorbed onto the G ranged between 2.47 and 3.98 Å depending on the structure of PAH molecule. The Non-Covalent Interactions (NCI) plot supports the concept that van der Waals interactions were involved in PAH adsorption onto the Graphene (G) structure. Based on the DFT-calculated adsorption energy data, a rapid and reliable method employing an empirical model of a quantitative structure–activity relationship (QSAR) was created and validated for estimating the adsorption energies of PAH molecules onto graphene.

The Bifurcated σ-Hole···σ-Hole Stacking Interactions

The bifurcated σ-hole···σ-hole stacking interactions between organosulfur molecules, which are key components of organic optical and electronic materials, were investigated by using a combined method of the Cambridge Structural Database search and quantum chemical calculation. Due to the geometric constraints, the binding energy of one bifurcated σ-hole···σ-hole stacking interaction is in general smaller than the sum of the binding energies of two free monofurcated σ-hole···σ-hole stacking interactions. The bifurcated σ-hole···σ-hole stacking interactions are still of the dispersion-dominated noncovalent interactions. However, in contrast to the linear monofurcated σ-hole···σ-hole stacking interaction, the contribution of the electrostatic energy to the total attractive interaction energy increases significantly and the dispersion component of the total attractive interaction energy decreases significantly for the bifurcated σ-hole···σ-hole stacking interaction. Another important finding of this study is that the low-cost spin-component scaled zeroth-order symmetry-adapted perturbation theory performs perfectly in the study of the bifurcated σ-hole···σ-hole stacking interactions. This work will provide valuable information for the design and synthesis of novel organic optical and electronic materials.

Halogen bonds in the crystal structure of 4,3′:5′,4″-terpyridine — 1,3-diiodotetrafluorobenzene (1/1), C21H11F4I2N3

C21H11F4I2N3, orthorhombic, Pnma (no. 62), a = 11.0042(4) Å, b = 20.6209(5) Å, c = 9.2371(3) Å, V = 2096.05(11) Å3, Z = 4, R gt (F) = 0.0316, wR ref (F 2) = 0.0556, T = 293(2) K.

Chalcogen bonds in the crystal structure of 4,7-dibromo-2,1,3-benzoselenadiazole, C6H2Br2N2Se

C6H2Br2N2Se, monoclinic, P21/c (no. 14), a = 7.7277(4) Å, b = 19.6360(6) Å, c = 10.8656(5) Å, β = 102.124(4)°, V = 1611.98(12) Å3, Z = 4, R gt (F) = 0.0482, wR ref (F 2) = 0.1175, T = 290 K.

Macrocycle-Functionalized RGO for Gas Sensors for BTX Detection Using a Double Transduction Mode

To fabricate mass and resistive sensors based on reduced graphene oxide (RGO), we investigated the functionalization of RGO by tetra tert-butyl phthalocyanine (PcH2tBu), which possesses a macroring and tert-butyl peripheral groups. Herein, we present the gas sensor responses of the functionalized RGO toward benzene, toluene, and xylene (BTX) vapors. The RGO was obtained by the reduction of graphene oxide (GO) using citrate as a reducing agent, while the functionalization was achieved non-covalently by simply using ultrasonic and heating treatment. The sensor devices based on both QCM (quartz crystal microbalance) and resistive transducers were used simultaneously to understand the reactivity. Both the GO and the RGO showed less sensitivity to BTX vapors, while the RGO/PcH2tBu presented enhanced sensor responses. These results show that the p-network plays a very important role in targeting BTX vapors. The resistive response analysis allowed us to state that the RGO is a p-type semiconductor and that the interaction is governed by charge transfer, while the QCM response profiles allowed use to determine the differences between the BTX vapors. Among BTX, benzene shows the weakest sensitivity and a reactivity in the higher concentration range (>600 ppm). The toluene and xylene showed linear responses in the range of 100–600 ppm.

Benzotrithiophene-based MOFs: interchromophoric interactions affected Ln(III) crystallization selectivity and optoelectronic properties

Metal-organic frameworks (MOFs) provide an ideal platform for the assembly of chromophores and thus show wide potential applications in optoelectronic devices. The spatial arrangement and interaction of the incorporated chromophores play a key role in the generation of coherent optical and electronic properties. In this work, two series of benzo-(1,2;3,4;5,6)-tristhiophene (BTT) based Ln-MOFs (Ln-1s and Ln-2s) were synthesized. These two series of MOFs present different assembly states of BTT chromophores, that is, BTT-containing ligands exist as separated monomers in Ln-1s but gather as dimers in Ln-2s. From the comparison between these two series of MOFs and theoretical calculations, we show for the first time that this chromophore assembly state difference could affect the crystallization selectivity of MOFs towards different Ln³⁺ ions. In addition, the interaction between BTT chromophores in the dimer also leads to the red-shifted photoluminescence and enhanced photocurrent of Ln-2s relative to those of Ln-1s. The results of this work demonstrate the multiple functions of interchromophoric interactions in the structures and optoelectronic properties of MOFs.

Development of Graphene-Based Polymeric Nanocomposites: A Brief Overview

Graphene (G) and its derivatives, such as graphene oxide (GO) and reduced GO (rGO), have outstanding electrical, mechanical, thermal, optical, and electrochemical properties, owed to their 2D structure and large specific surface area. Further, their combination with polymers leads to novel nanocomposites with enhanced structural and functional properties due to synergistic effects. Such nanocomposites are becoming increasingly useful in a wide variety of fields ranging from biomedicine to the electronics and energy storage applications. In this review, a brief introduction on the aforementioned G derivatives is presented, and different strategies to develop polymeric nanocomposites are described. Several functionalization methods including covalent and non-covalent approaches to increase their interaction with polymers are summarized, and selected examples are provided. Further, applications of this type of nanocomposites in the field of energy are discussed, including lithium-ion batteries, supercapacitors, transparent conductive electrodes, counter electrodes of dye-sensitized solar cells, and active layers of organic solar cells. Finally, the challenges and future outlook for G-based polymeric nanocomposites are discussed.

Insight into the Mechanisms of Low Coverage Adsorption of N-Alcohols on Single Walled Carbon Nanohorn

We report for the first time the chromatographic study of n-alcohols (from methanol to butanol) adsorption on single walled carbon nanohorn (SWCNH). Using measured temperature dependence of adsorption isotherms (373-433 K) the isosteric adsorption enthalpy is calculated and compared with the data reported for a graphite surface. It is concluded that a graphite surface is more homogeneous, and the enthalpy of adsorption on SWCNHs at zero coverage correlates well with molecular diameter and polarizability, suggesting leading role of dispersive interactions, i.e., no heteroatoms presence in the walls of SWCNH structures. Next using modern DFT approach we calculate the energy of n-alcohols interactions with a graphene sheet and with a single nanocone finally proposing a more realistic-double nanocone model. Obtained results suggest alcohols entrapping between SWCNH with OH groups located toward nanocones ends, leading to the conclusions about very promising future applications of SWCNHs in catalytic reactions with participation of n-alcohols.

BODIPY dimers: structure, interaction, and absorption spectrum

The object of the present study are BODIPY molecules obtained previously by Piskorz et al. (Dyes Pigm. 178:108322, 2020) for their antimicrobial activity. Structural analysis of the BODIPY dimers is presented in context of the aggregation influence on the photophysical properties. The thorough investigation of the nature of intermolecular interaction in the representative BODIPY dimers is provided together with the decomposition of the interaction energy into the components of well-defined origin according to SAPT procedure. For the model BODIPY systems the careful examination of the interaction nature for the dimer structure based on experimental crystal study as well as fully optimized is given. The tendencies observed in the model dimers are further on investigated for two pairs of BODIPY systems designed for biomedical application. The analyzed molecules are shown to maximize the mutual interaction by the optimization of the stacking dispersion contacts between the aromatic rings of the molecules, therefore producing stable dimers. The estimation of SAPT0 interaction energy components confirms the dominating dispersion character arising from mutual BODIPY core contacts. The influence of the dimerization process on the photophysical properties of the systems studied theoretically depends to the high extend on the dimerization mode and is significant for parallel and antiparallel dispersion-governed dimers.

Fabrication of BP2T functionalized graphene via non-covalent π–π stacking interactions for enhanced ammonia detection

Graphene has stimulated great enthusiasm in a variety of fields, while its chemically inert surface still remains challenging for functionalization towards various applications. Herein, we report an approach to fabricate non-covalently functionalized graphene by employing π–π stacking interactions, which has potentialities for enhanced ammonia detection. 5,5′-Di(4-biphenylyl)-2,2′-bithiophene (BP2T) molecules are used in our work for the non-covalent functionalization through strong π–π interactions of aromatic structures with graphene, and systematic investigations by employing various spectroscopic and microscopic characterization methods confirm the successful non-covalent attachment of the BP2T on the top of graphene. From our gas sensing experiments, the BP2T functionalized graphene is promising for ammonia sensing with a 3-fold higher sensitivity comparing to that of the pristine graphene, which is mainly attributed to the enhanced binding energy between the ammonia and BP2T molecules derived by employing the Langmuir isotherm model. This work provides essential evidence of the π–π stacking interactions between graphene and aromatic molecules, and the reported approach also has the potential to be widely employed in a variety of graphene functionalizations for chemical detection.

Non-covalent functionalization of graphene has been achieved by employing π–π stacking interactions, and it is promising for ammonia detection with greatly enhanced sensitivity.

The σ-hole⋯σ-hole stacking interaction: An unrecognized type of noncovalent interaction

The σ-hole⋯σ-hole stacking interaction, an unrecognized type of noncovalent interaction, has been found to be present in large quantities in the Cambridge Structural Database. In the σ-hole⋯σ-hole stacking interaction, each of the two interacting σ-holes has the dual electron donor/electron acceptor character; when one σ-hole acts as an electron donor, the other σ-hole acts as an electron acceptor, and vice versa. The σ-hole⋯σ-hole stacking interaction is clearly different from the σ-hole bond in which the charge transfer occurs mainly from the electron donor to the σ-hole. Energy component analysis shows that the σ-hole⋯σ-hole stacking interaction is dominated by the dispersion energy, which is similar to the nature of the aromatic stacking interaction between unsaturated molecules or the σ⋯σ stacking interaction between saturated molecules.

Nature of intermolecular interaction in squaraine dimers

Squaraine dyes are known for their particular optical properties. They exhibit intense photochemically stable fluorescence in usually (near) infra red region that can be quenched by intermolecular interactions. Moreover, even the centrosymmetric dyes feature non-zero second harmonic generation upon aggregation. Therefore, the detailed knowledge of the squaraine dye interaction nature both in homogenic aggregates and with other species present in the environment can be of importance for the design of new materials of desired properties. In the present study, interaction in squaraine dimers is investigated with quantum chemistry tools. Four structures: two stacked and two hydrogen-bonded are analyzed in terms of supermolecular approach and symmetry-adapted perturbation theory. MP2C/aug-cc-pVTZ supermolecular calculations confirm the particular stability of the stacked dimers and the favoured dispersion attraction for the long-displaced system.

Strong dependence of the vertical charge carrier mobility on the π-π stacking distance in molecule/graphene heterojunctions

Due to mechanical flexibility and low cost, heterojunctions consisting of graphene and small organic molecules are regarded as promising candidate materials for vertical organic field-effect transistors (VOFETs), where the charge carrier mobility perpendicular to the graphene plane is crucial to their performance. Herein, through density functional simulations, we find that the vertical charge carrier mobility of the heterojunctions can be greatly adjusted by tuning their π-π stacking distances. For the 6,13-dichloropentacene (DCP)/graphene heterojunctions, with the distance between the first DCP layer and graphene decreasing to below 2.4 Å, the vertical electron mobility between DCP layers is improved dramatically while the vertical hole mobility is greatly reduced. The strong dependence of vertical charge carrier mobility on the distance between the first molecular layer and substrate for smaller values than the typical π-π stacking distance (3.3-3.8 Å) was also observed in the perylenetetracarboxylic dianhydride (PTCDA)/graphene and DCP/hexagonal-BN heterojunctions, where the tendency is very different to that of the DCP/graphene heterojunction. Our simulation results enabled us to develop a new strategy to tune the vertical charge transport properties in molecule/graphene heterojunctions, which provides insights into developing efficient VOFETs.

Weak Intermolecular Interactions in Covalent Organic Framework-Carbon Nanofiber Based Crystalline yet Flexible Devices

The redox-active and porous structural backbone of covalent organic frameworks (COFs) can facilitate high-performance electrochemical energy storage devices. However, the utilities of such 2D materials as supercapacitor electrodes in advanced self-charging power-pack systems have been obstructed due to the poor electrical conductivity and subsequent indigent performance. Herein, we report an effective strategy to enhance the electrical conductivity of COF thin sheets through the in situ solid-state inclusion of carbon nanofibers (CNF) into the COF precursor matrix. The obtained COF-CNF hybrids possess a significant intermolecular π···π interaction between COF and the graphene layers of the CNF. As a result, these COF-CNF hybrids (DqTp-CNF and DqDaTp-CNF) exhibit good electrical conductivity (0.25 × 10^-3 S cm^-1), as well as high performance in electrochemical energy storage (DqTp-CNF: 464 mF cm^-2 at 0.25 mA cm^-2). Also, the fabricated, mechanically strong quasi-solid-state supercapacitor (DqDaTp-CNF SC) delivered an ultrahigh device capacitance of 167 mF cm^-2 at 0.5 mA cm^-2. Furthermore, we integrated a monolithic photovoltaic self-charging power pack by assembling DqDaTp-CNF SC with a perovskite solar cell. The fabricated self-charging power pack delivered excellent performance in the areal capacitance (42 mF cm^-2) at 0.25 mA cm^-2 after photocharging for 300 s.

Nanographene favors electronic interactions with an electron acceptor rather than an electron donor in a planar fused push-pull conjugate

A combination of a preexfoliated nanographene (NG) dispersion and fused electron donor-acceptor tetrathiafulvalene-perylenediimide (TTF-PDI) results in a noncovalent functionalization of NG. Such novel types of nanohybrids were characterized by complementary spectroscopic and microscopic techniques. The design strategy of the chromophoric and electroactive molecular conjugate renders a large and planar π-extended system with a distinct localization of electron-rich and electron-poor parts at either end of the molecular conjugate. Within the in situ formed nanohybrid, the conjugate was found to couple electronically with NG preferentially through the electron accepting PDI rather than the electron donating TTF and to form the one-electron reduced form of PDI, which corresponds to p-doping of graphene.

Pyrene-based MOFs as fluorescent sensors for PAHs: an energetic pathway of the backbone structure effect on response

The sensing performance of metal-organic frameworks (MOFs), a novel kind of crystalline fluorescent sensing materials, would be profoundly affected by their backbone structures. The current understanding about the backbone effect is limited to the modulation of analyte accommodation through pore structures. Herein, three topologically different pyrene-based MOFs, including NU-1000, NU-901 and ROD-7, were investigated as potential fluorescent sensors for polycyclic aromatic hydrocarbons (PAHs). Although these MOFs are constructed by the same photoactive component, they exhibited distinct sensing behaviors. NU-1000 gave different forms of fluorescent response to acenaphthylene, pyrene and fluoranthene with detection limits at the ng L-1 level. In contrast, NU-901 and ROD-7 were unresponsive to all tested PAHs. Experimental and computational investigations illustrate that this distinction is due to the variance in the excited state energy. The strong inter-ligand interaction in NU-901 and ROD-7 lowers their excited state energy and thus thermodynamically inhibits the photo-induced electron transfer and excimer/exciplex formation, which works in the NU-1000 system. This work proves for the first time that the topological structure of MOFs could affect their sensing performance in an energetic way.

Density Functional Study on the Adsorption of 5-Membered N-Heterocycles on B/N/BN-Doped Graphene: Coronene as a Model System

Adsorption of seven 5-membered N-heterocycles on B/N/BN-doped graphene (with coronene as a model system) has been studied using density functional theory (DFT). The geometry of the complexes validated the involvement of both π···π stacking and N-H···π interaction in the adsorption process. The stability of the complexes is measured in terms of stabilization energy, and the results suggested that the complexes are stable enough (stabilization energies are in the range of 7.61-14.77 kcal mol^-1). Studies confirmed the stability of complexes in the solvent phase too irrespective of the dielectric of the solvent. Dispersive force is the major mode of interaction in stabilizing the complexes. Natural bond orbital analysis indicated a small contribution from electrostatic and covalent interactions. Thermochemical analysis revealed that the complexation is exothermic in nature and favorable at a lower temperature. Adsorption of N-heterocycles exerts a nominal impact on the electronic properties of the undoped/doped graphene. The study presents a simple approach to introduce an arbitrary functionality to undoped/doped graphene by preserving its electronic properties.

Can Adsorption on Graphene be Used for Isotopic Enrichment? A DFT Perspective

We have explored the theoretical applicability of adsorption on graphene for the isotopic enrichment of aromatic compounds. Our results indicate that for nonpolar molecules, like benzene, the model compound used in these studies shows a reasonable isotopic fractionation that is obtained only for the deuterated species. For heavier elements, isotopic enrichment might be possible with more polar compounds, e.g., nitro- or chloro-substituted aromatics. For benzene, it is also not possible to use isotopic fractionation to differentiate between different orientations of the adsorbed molecule over the graphene surface. Our results also allowed for the identification of theory levels and computational procedures that can be used for the reliable prediction of the isotope effects on adsorption on graphene. In particular, the use of partial Hessian is an attractive approach that yields acceptable values at an enormous increase of speed.

In silico study of Bombyx mori fibroin enhancement by graphene in acidic environment

Bombyx mori fibroin has been widely used since a long time ago and has become a popular material. Here, we carry out a molecular dynamics simulation-based docking simulation of a small fragment of graphene in order to seek the best binding position on the N-termini domain of Bombyx mori fibroin. We report the best binding position, of which binding free energy falls at -54.8 kJ mol-1, indicating the strong binding. The further analysis of the binding pathway shows that this position is selective for single layered graphene rather than multi-layered graphene within our limited simulation times. Via comparing the RAMAN spectra of the corresponding binding pose of atomic clusters, we report the change in the bands compared with free standing graphene fragments, implying the change in molecular orbitals.

Structural, optoelectronic and charge transport properties of the complexes of indigo encapsulated in carbon nanotubes

Using the dispersion-corrected density functional B97D and 6-31g(d,p) basis set, the structural, stability, electronic, optical and charge transport properties of the complexes formed by encapsulating indigo inside carbon nanotubes (CNTs) of varying diameters are investigated. Based on the stabilization energy of the complexes indigo@(n,n)CNT (where n = 6, 7 and 8), indigo@(7,7)CNT is shown to be the most stable owing to the ideal diameter of (7,7)CNT for encapsulating indigo. The nature of the interaction between the guest and the host is investigated by means of energy decomposition analysis employing the symmetry adapted perturbation theory. Electronic properties such as the ionization energy, the electron affinity and the energy gap between the highest occupied and lowest unoccupied molecular orbitals (ΔEH-L) of the complexes are determined. The low values of ΔEH-L (<1 eV) for the complexes suggest that they can act as narrow energy gap semiconductors. All the complexes exhibit high hole and electron mobilities which vary inversely with respect to the diameter of the CNT. Using the time-dependent density functional theoretical method, the absorption properties are predicted for the most stable complex indigo@(7,7)CNT. The presence of charge transfer peaks in the visible and near-infrared regions of the electromagnetic spectrum suggests that the complexes are suitable for optoelectronic devices such as solar cells.

Polycyclic Aromatic Hydrocarbons Adsorption onto Graphene: A DFT and AIMD Study

Density functional theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations were performed to understand graphene and its interaction with polycyclic aromatic hydrocarbons (PAHs) molecules. The adsorption energy was predicted to increase with the number of aromatic rings in the adsorbates, and linearly correlate with the hydrophobicity of PAHs. Additionally, the analysis of the electronic properties showed that PAHs behave as mild n-dopants and introduce electrons into graphene; but do not remarkably modify the band gap of graphene, indicating that the interaction between PAHs and graphene is physisorption. We have also discovered highly sensitive strain dependence on the adsorption strength of PAHs onto graphene surface. The AIMD simulation indicated that a sensitive and fast adsorption process of PAHs can be achieved by choosing graphene as the adsorbent. These findings are anticipated to shed light on the future development of graphene-based materials with potential applications in the capture and removal of persistent aromatic pollutants.

Theoretical study of gas and solvent phase stability and molecular adsorption of noncanonical guanine bases on graphene

The gas and solvent phase stability of noncanonical (Gua)_n nucleobases is investigated in the framework of dispersion-corrected density functional theory (DFT). The calculated results strongly support the high tendency for the dimerization of (Gua)_n bases in both gas and solvent phases. An interplay between intermolecular and bifurcated H-bonds is suggested to govern the stability of (Gua)_n bases which bears a correlation with the description of dispersion correction terms employed in the DFT calculations. For example, a higher polarity is predicted for (Gua)_n bases by the dispersion-corrected DFT in contrast to the non-polar nature of (Gua)₃ and (Gua)₄ predicted by the hybrid meta-GGA calculations. This distinct variation becomes significant under physiological conditions as polar (Gua)_n is likely to exhibit greater stabilization in the gas phase compared to solvated (Gua)_n. Graphene acting as a substrate induces modification in base configurations via maximization of π-orbital overlap between the base and substrate. In solvent, the substrate-induced effects are further heightened with lowering of the dipole moments of (Gua)_n as also displayed by the corresponding isosurface of the electrostatic potential. The graphene-induced stability in both gas and solvent phases appears to fulfill one of the prerequisite criteria for molecular self-assembly. The DFT results therefore provide atomistic insights into the stability and molecular assembly of free-standing noncanonical (Gua)_n nucleobases which can be extended to understanding the self-assembly process of functional biomolecules on 2D materials for potential biosensing applications.

Theoretical investigations into the charge transfer properties of thiophene α-substituted naphthodithiophene diimides: excellent n-channel and ambipolar organic semiconductors

A theoretical study was carried out to investigate the electronic structures and the charge transport properties of a series of naphthodithiophene diimide (NDTI) thiophene α-substituted derivatives NDTI-X using density functional theory and classical Marcus charge transfer theory. This study deeply revealed the structure-property relationships by analyzing the intermolecular interactions in crystal structures of C8-NDTI and C8-NDTI-Cl thoroughly by using the Hirshfeld surface, QTAIM theories and symmetry-adapted perturbation theory (SAPT). Our results suggested that a 2-D brick-like π-stacking structure makes C8-NDTI-Cl a more excellent n-type semiconducting material with μ_max-e of 2.554 cm² V^-1 s^-1 than C8-NDTI with a herringbone-like slipped π-stacking motif. In addition, the calculated results showed that by modifying the thiophene α-positions of NDTI with electron-withdrawing substituents, -F, -Cl and -CN, low-lying LUMO energy levels and a high adiabatic electron affinity EA(a) can be obtained; while introducing electron-donating groups, benzene (-B), thiophene (-T), benzo[b]thiophene (-BT) and naphtha[2,3-b]thiophene (-NT), expanded the molecular π-conjugated backbone, and narrow band gaps, high EA(a) and small reorganization energies can be obtained. Theoretical simulations predict that NDTI-CN is an excellent air-stable n-type organic semiconducting material with an average electron mobility μ_e of up to 1.743 cm² V^-1 s^-1. Owing to their high EA(a), moderate adiabatic ionization potential IP(a) as well as small hole and electron reorganization energies, NDTI-BT and NDTI-NT are two well-balanced air-stable ambipolar semiconducting materials. The theoretical average hole/electron mobilities are as high as 2.708/3.739 cm² V^-1 s^-1 for C8-NDTI-NT and 1.597/2.350 cm² V^-1 s^-1 for C8-NDTI-BT, respectively.

Approximate quantum chemical methods for modelling carbohydrate conformation and aromatic interactions: β-cyclodextrin and its adsorption on a single-layer graphene sheet

Adsorption of carbohydrates on graphene has the potential to improve graphene dispersibility in water. Here we assess the ability of DFTB-based and NDDO-based quantum chemical methods to model β-cyclodextrin conformations and interactions with graphene.

Noncovalent Interaction of Graphene with Heterocyclic Compounds: Benzene, Imidazole, Tetracene, and Imidazophenazines

Noncovalent functionalization of graphene with organic molecules offers a direct route to multifunctional modification of this nanomaterial, leading to its various possible practical applications. In this work, the structures of hybrids formed by linear heterocyclic compounds such as imidazophenazine (F1) and its derivatives (F2-F4) with graphene and the corresponding interaction energies are studied by using the DFT method. Special attention is paid to the hybrids where the attached molecule is located along the graphene zigzag (GZZ ) and armchair (GAC ) directions. The interaction energies corresponding to the graphene hybrids of the F1-F4 compounds for the two directions are found to be distinct, while tetracene (being a symmetrical molecule) shows a small difference between these binding energies. It is found that the back-side CH3 and CF3 groups have an important influence on the arrangements of F1 derivatives on graphene and on their binding energies. The contribution of the CF3 group to the total binding energy of the F3 molecule with graphene is the largest (3.4 kcal mol(-1) ) (the GZZ direction) while the CH3 group increases this energy of F2 only by 2.0 kcal mol(-1) (the GAC direction). It is shown that replacing the carbons with other atoms or adding a back-side group enables one to vary the polarizability of graphene.

Adsorptive Separation of Methanol-Acetone on Isostructural Series of Metal-Organic Frameworks M-BTC (M = Ti, Fe, Cu, Co, Ru, Mo): A Computational Study of Adsorption Mechanisms and Metal-Substitution Impacts

The adsorptive separation properties of M-BTC isostructural series (M = Ti, Fe, Cu, Co, Ru, Mo) for methanol-acetone mixtures were investigated by using various computational procedures of grand canonical Monte Carlo simulations (GCMC), density functional theory (DFT), and ideal adsorbed solution theory (IAST), following with comprehensive understanding of adsorbate-metal interactions on the adsorptive separation behaviors. The obtained results showed that the single component adsorptions were driven by adsorbate-framework interactions at low pressures and by framework structures at high pressures, among which the mass effects, electrostatics, and geometric accessibility of the metal sites also played roles. In the case of methanol-acetone separation, the selectivity of methanol on M-BTCs decreased with rising pressures due to the pressure-dependent separation mechanisms: the cooperative effects between methanol and acetone hindered the separation at low pressures, whereas the competitive effects of acetone further resulted in the lower selectivity at high pressures. Among these M-BTCs, Ti and Fe analogues exhibited the highest thermodynamic methanol/acetone selectivity, making them promising for adsorptive methanol/acetone separation processes. The investigation provides mechanistic insights on how the nature of metal centers affects the adsorption properties of MOFs, and will further promote the rational design of new MOF materials for effective gas mixture separation.