4‐(3,5‐Dimethyl‐1H‐pyrazol‐4‐ylmethyl)‐3,5‐dimethyl‐1H‐pyrazol‐2‐ium dihydrogen phosphate: a combined X‐ray and DFT study

The molecular structure of the title salt, C₁₁H₁₇N₄⁺·H₂PO₄⁻, has been determined from single‐crystal X‐ray analysis and compared with the structure calculated by density functional theory (DFT) at the BLYP level. The crystal packing in the title compound is stabilized primarily by intermolecular N—H...O, O—H...N and O—H...O hydrogen bonds and π–π stacking interactions, and thus a three‐dimensional supramolecular honeycomb network consisting of R₄²(10), R₄⁴(14) and R₄⁴(24) ring motifs is established. The HOMO–LUMO energy gap (1.338 eV; HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital) indicates a high chemical reactivity for the title compound.     

Theoretical investigations on the carbazole‐based conjugated polymers containing electron‐donating divinylaryl

The polycarbazoles have been proved to efficiently suppress the keto defect emission. Three carbazole‐based conjugated polymers, poly[9‐methyl‐3‐(4‐vinylstyryl)‐9H‐carbazole] (PBC), poly[9‐methyl‐3‐(2‐(5‐vinylthiophen‐2‐yl)vinyl)‐9H‐carbazole] (PBT) and poly[9‐methyl‐3‐(2‐(5‐vinylfuran‐2‐yl)vinyl)‐9H‐carbazole] (PBF), were investigated by quantum‐chemical techniques, and gain a detailed understanding of the influence of carbazole units and the introduction of electron‐donating on the electronic and optical properties. The electronic properties of the neutral molecules, HOMO‐LUMO gaps (ΔE), in addition to ionization potential (I_p) and electron affinity (E_a), are studied using B3LYP density functional theory. The lowest excitation energies (E_g) and the absorption wavelength are studied using the time dependent density functional theory (TDDFT). The calculated results show that all three series of polymers have good planarity. And the highest‐occupied molecular orbital (HOMO) energies lift about 0.36–0.61 eV and thus the I_P decrease about 0.01–0.19 eV compared to polycarbazole, suggesting the significant improved hole‐accepting and transporting abilities. By introducing the electron‐donating 1,4‐divinylphenylene or 2,5‐divinylthiophene or 2,5‐divinylfuran units in the backbone, and the lowest‐unoccupied molecular orbital (LUMO) energies decrease 0.20–0.39 eV. In addition, PBC, PBT and PBF have longer maximal absorption wavelengths than polycarbazole. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 706–714, 2009     

Photo‐physical Properties of N‐methyl‐3,4‐fulleropyrrolidine and Its Derivatives: A DFT and TD‐DFT Investigation

A series of N‐methyl‐3,4‐fulleropyrrolidine (NMFP) derivatives were designed by selecting different π‐conjugated linkers and electron‐donating groups as D‐π‐A and D‐A systems. The optimised structures and photo‐physical properties of NMFP and its derivatives have been determined using density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods with the B3LYP functional and the 6‐31G basis set. According to the computation analysis, both the π‐conjugated linkers and the electron‐donating groups can influence the electronic and photo‐physical properties of the NMFP derivatives. Our calculated results demonstrated that the electron‐donating groups, with significant electron‐donating ability, had the tendency to increase the highest occupied molecular orbital (HOMO) energy. The π‐conjugated linkers with lower resonance energy decreased the lowest occupied molecular orbital (LUMO) energy and caused a significant decrease in the energy gap (E_g) between the E_HOMO and E_LUMO. A Natural Bond Orbital (NBO) analysis examines the effect of the electron‐donating group, π conjugated linker, and electron‐withdrawing group for these NMFP derivatives. For the NMFP derivatives, a projected density of state (PDOS) analysis demonstrated that the electron density of HOMO and LUMO are concentrated on the electron‐donating group and the π‐conjugated linker, respectively. A TD‐DFT/B3LYP calculation was performed to calculate the electronic absorption spectra of these NMFP derivatives. Both the electron‐donating group and the π‐conjugated linker contribute to the major absorption peaks, which are assigned as HOMO to LUMO transitions and are red‐shifted relative to those of non‐substituted NMFP.     

Derivatizing Tribenzothiophene‐Fused Hexa‐peri‐hexabenzocoronenes with Tunable Optoelectronic Properties

A series of trisbenzothieno[1,2:7,8:13,14]hexa‐peri‐hexabenzocoronenes were synthesized and characterized by a combination of NMR, 2D NMR, MALDI‐TOF MS, UV/Vis absorption spectroscopy, and 2D‐WAXS measurement. By structural modulation like decoration of electro‐donating alkoxyl chain, and conversion from an electron‐rich thiophene ring into an electron‐poor thiophene‐S,S‐dioxide moiety, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the hexabenzocoronenes derivatives can be effectively tuned which is further verified by the DFT calculations and cyclic voltammetry.     

Electronic structure and stability of binary and ternary aluminum‐bismuth‐nitrogen nanoclusters

The electronic structure and stability in binary and ternary aluminum‐bismuth‐nitrogen nanoclusters up to six atoms are studied using density functional theory (DFT). The lowest energy geometries were obtained by sampling the geometrical space with a Monte Carlo method and geometry optimizations, at DFT level, with M06L functional. The clusters stability is analyzed using formation and fragmentation energies. Our results show that a high concentration of nitrogen presents a tendency to form nitrogen clusters. highest occupied molecular orbital‐lowest unoccupied molecular orbital gaps show the well‐known oscillation as the number of atoms is increased. Bonding between Al, Bi, and N has mainly a π character. Bismuth and aluminum atoms tend to promote high multiplicity states in small clusters. These new binary and ternary materials provide a potential new field in optoelectronics and high energetic material compounds. © 2014 Wiley Periodicals, Inc.     

Characterizing the Intermediates Compound I and II in the Cytochrome P450 Catalytic Cycle with Nonlinear X‐ray Spectroscopy: A Simulation Study

Cytochrome P450 enzymes are an important family of biocatalysts that oxidize chemically inert C?H bonds. There are many unresolved questions regarding the catalytic reaction intermediates, in particular P450 Compound I (Cpd‐I) and II (Cpd‐II). By using simple molecular models, we simulate various X‐ray spectroscopy signals, including X‐ray absorption near‐edge structure (XANES), resonant inelastic X‐ray scattering (RIXS), and stimulated X‐ray Raman spectroscopy (SXRS) of the low‐ and high‐spin states of Cpd‐I and II. Characteristic peak patterns are presented and connected to the corresponding electronic structures. These X‐ray spectroscopy techniques are complementary to more conventional infrared and optical spectroscopy and they help to elucidate the evolving electronic structures of transient species along the reaction path.     

Synthesis,solid‐state,and charge‐transport properties of conjugated polythiophene‐S,S‐dioxides

An alkylated semiconducting polymer comprising alternating bithiophene‐[all]‐S,S‐dioxide and aromatic monothiophene units in the polymer backbone was synthesized with the intent of modifying the energy gap and lowest unoccupied molecular orbital for use as a stable n‐type semiconductor. Films spun from this semiconducting polymer were characterized utilizing X‐ray scattering, near edge X‐ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy, and thin‐film field effect transistors to determine how oxidation of the thiophene ring systems impacts the structural and electronic properties of the polymer. The thiophene‐S,S‐dioxide polymers have lower optical and electrical band gaps than corresponding thiophene polymers. X‐ray scattering results indicate that the polymers are well ordered with the π–π stacking distances increased by 0.4 Å relative to analogous thiophene polymers. The electrical stability of these polymers is poor in transistors with a drop in the field effect mobility by approximately one order of magnitude upon addition of just 5% of the thiophene‐S,S‐dioxide unit in a copolymer with thiophene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Ti‐Based Catalysts and Photocatalysts: Characterization and Modeling

This perspective article aims to underline how cutting‐edge synchrotron radiation spectroscopies such as extended X‐ray absorption spectroscopy (EXAFS), X‐ray absorption near edge structure (XANES), high resolution fluorescence detected (HRFD) XANES, X‐ray emission spectroscopy (XES) and resonant inelastic X‐ray scattering (RIXS) have played a key role in the structural and electronic characterization of Ti‐based catalysts and photocatalysts, representing an important additional value to the outcomes of conventional laboratory spectroscopies (UV‐Vis, IR, Raman, EPR, NMR etc.). Selected examples are taken from the authors research activity in the last two decades, covering both band‐gap and shape engineered TiO₂ materials and microporous titanosilicates (ETS‐10, TS‐1 and Ti?AlPO‐5). The relevance of the state of the art simulation techniques as a support for experiments interpretation is underlined for all the reported examples.     

Electron smearing in DFT calculations: A case study of doxorubicin interaction with single‐walled carbon nanotubes

To address the choice of an appropriate value of electron smearing to facilitate self‐consistent field (SCF) convergence, we studied the interaction of doxorubicin with short armchair and zigzag single‐walled carbon nanotube models with closed caps, at the PWC/DNP level of density functional theory. By gradually reducing the electron smearing value from a large and most commonly used one of 0.005 Ha to zero (Fermi occupation), we monitored the changes in close contacts between the interacting species, total energy of the molecular system, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy and isosurfaces, HOMO‐LUMO gap energy, and plots of electrostatic potential. It became evident that the commonly used smearing values of ≥0.001 Ha can alter the results significantly (for example, by one order of magnitude for HOMO–LUMO gap energy). We suggest the setting of electron smearing value at 0.0001 Ha, which does not imply too high computation cost and can guarantee the results close to the ones obtained with Fermi occupation. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Chemical Speciation and Bond Lengths of Organic Solutes by Core‐Level Spectroscopy: pH and Solvent Influence on p‐Aminobenzoic Acid

Through X‐ray absorption and emission spectroscopies, the chemical, electronic and structural properties of organic species in solution can be observed. Near‐edge X‐ray absorption fine structure (NEXAFS) and resonant inelastic X‐ray scattering (RIXS) measurements at the nitrogen K‐edge of para‐aminobenzoic acid reveal both pH‐ and solvent‐dependent variations in the ionisation potential (IP), 1s→π* resonances and HOMO–LUMO gap. These changes unequivocally identify the chemical species (neutral, cationic or anionic) present in solution. It is shown how this incisive chemical state sensitivity is further enhanced by the possibility of quantitative bond length determination, based on the analysis of chemical shifts in IPs and σ* shape resonances in the NEXAFS spectra. This provides experimental access to detecting even minor variations in the molecular structure of solutes in solution, thereby providing an avenue to examining computational predictions of solute properties and solute–solvent interactions.     

The self‐consistent charge density functional tight‐binding theory study of carbon adatoms using tuned Hubbard U parameters

The self‐consistent charge density functional tight‐binding (DFTB) theory is a useful tool for realizing the electronic structures of large molecular complex systems. In this study, the electronic structure of C₆₁ formed by fullerene C₆₀ with a carbon adatom is analyzed, using the fully localized limit and pseudo self‐interaction correction methods of DFTB to adjust the Hubbard U parameter (DFTB + U). The results show that both the methods used to adjust U can significantly reduce the molecular orbital energy of occupied states localized on the defect carbon atom and improve the gap between highest occupied molecular orbital(HOMO) and lowest unoccupied molecular orbital(LUMO) of C₆₁. This work will provide a methodological reference point for future DFTB calculations of the electronic structures of carbon materials.     

X‐ and H‐Shape Two Dimensional Conjugated Oligomers with Anthracene as the Node

X‐ and H‐shape two‐dimensional (2D) conjugated oligomers (X‐ and H‐mers) and relevant model compounds have been synthesized through the introduction of different conjugated segments at the 9,10 and 2,6‐positions of anthracene, and their properties were studied in detail. Comparing with the model compounds, the X‐ and H‐mers are featured with broader absorption spectra and narrower energy bandgaps. Computational studies on the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) also indicate that these X‐ and H‐mers are 2D conjugated. Solution processed bulk heterojunction (BHJ) solar cells with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) as the acceptor material exhibited the power conversion efficiency (PCE) up to 0.53 %.     

Dicyano and pyridine derivatives of β-carotene: synthesis and vibronic, electronic, and photophysical properties

Density functional theory and time-dependent density functional theory calculations provide pictures of the molecular orbitals involved in the ground and excited states of two cyano derivatives of 8'-apo-β-caroten-8'-al synthesized via an acid-base-catalyzed Knoevenagel condensation reaction. Population analysis shows that the symmetry-allowed transition, S(0) ((1)A(g)) → S(2) ((1)B(u)) based on the C(2h) symmetry is a HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) π → π* transition with electron densities located mostly on the polyene chain. Calculated and actual steady-state absorption spectra show similar features with low-energy peak maxima between 550 and 600 nm.     

Synthesis,optical and electrochemical properties of arylenevinylene‐based π‐conjugated polymers with imidazolium units in the main chain

Arylenevinylene‐based π‐conjugated polymers containing imidazolium cationic units in the main chain and their model compounds were synthesized and characterized in terms of optical and electrochemical properties. 9,9‐Bisoctylfluorene, 2,5‐bisdodecyloxybenzene, and 3‐dodecylthiophene were introduced as arylene units with different donor characteristics to evaluate the effect on the highest occupied molecular orbital‐lowest unoccupied molecular orbital (HOMO‐LUMO) gap energy. The UV–vis and fluorescence spectra of cationic polymers and model compounds with iodide counter anion exhibited a significant blue shift with respect to the parent neutral molecules. X‐ray single crystal analysis for model compounds revealed that the effective π‐conjugation length of cationic model compounds decreased compared to the neutral model compounds by means of twisted conformation directed by CH‐π interactions between N‐methyl groups of imidazolium and neighboring aryl units. The cyclic voltammetry measurement suggested the negative shift of LUMO levels by the conversion of imidazole to imidazolium, indicating the electron‐accepting characteristics of cationic imidazolium unit. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Ab initio investigation of 2,2′‐bis(4‐trifluoromethylphenyl)‐5,5′‐bithiazole for the design of efficient organic field‐effect transistors

The initial molecular structure of 2,2′‐bis(4‐trifluoromethylphenyl)‐ 5,5′‐bithiazole has been optimized in the ground state using density functional theory (DFT). The distribution patterns of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have also been evaluated. To shed light on the charge transfer properties, we have calculated the reorganization energy of electron λ_e, the reorganization energy of hole λ_h, adiabatic electron affinity (EA_a), vertical electron affinity (EA_v), adiabatic ionization potential (IP_a), and vertical ionization potential (IP_v) using DFT. Based on the evaluation of hole reorganization energy, λ_h, and electron reorganization energy, λ_e, it has been predicted that 2,2′‐bis(4‐trifluoromethylphenyl)‐5,5′‐bithiazole would be a better electron transport material. Finally, the effect of electric field on the HOMO, LUMO, and HOMO–LUMO gap were observed to check its suitability for the use as a conducting channel in organic field‐effect transistors. © 2015 Wiley Periodicals, Inc.     

Anthracene‐thieno[3,4‐c]pyrrole‐4,6‐dione based donor–acceptor conjugated copolymers for applications in optoelectronic devices

Three novel alternating copolymers of thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) and triisopropylsilylacetylene‐functionalized anthracene were prepared via Suzuki polymerization. Various solubilizing substituents were attached to the TPD moiety in order to ascertain the impact they have upon the optical, electrochemical, and thermal properties of the resulting polymers. All copolymers showed good solubility and thermal stability with decomposition temperatures in excess of 300°C. Optical properties revealed that PTATPD(O), PTATPD(DMO), and PTATPD(BP) displayed optical energy gaps in excess of 2.0 eV. It is speculated that steric repulsion between solubilizing groups on repeat units along polymer chains reduces their planarity and decreases their electronic conjugation. The amorphous nature of the polymers was confirmed with differential scanning calorimetry and powder X‐ray diffraction. The highest occupied molecular orbital levels of the three polymers are unaffected by the different solubilizing chains. However, they exert some influence over the lowest unoccupied molecular orbital (LUMO) levels with PTATPD(BP) and PTATPD(O) displaying the lowest LUMO levels (?3.4 eV). In contrast, PTATPD(DMO) displayed the highest LUMO level (?3.3 eV). © 2015 The Authors. Polymers for Advanced Technologies Published by John Wiley & Sons Ltd.     

Molecular design of a π‐conjugated single‐chain electronically conductive polymer

This study demonstrates that single‐chain π‐conjugated systems can be made electrically conductive by modifying the molecular structures of both ends of the oligomers making up a polymer. That is, the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps of a fairly long polyyne‐type oligomer with appropriately modified molecular structures at both ends are found to be on the order of thermal energy by calculations using density functional theory (DFT) with B3LYP functionals. This result applies to molecular structures with characteristic bond alternations. The peculiar bond alternations are caused by competition between two effects of the bond alternations of the two mutually perpendicular π‐conjugated systems, which partially cancel each other out. It is probable that we can design one‐dimensional polymers with HOMO–LUMO gaps small enough to be conductive by combining the above‐mentioned oligomers with each other as monomer units in the polymer. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

A Non‐Fullerene Acceptor with Chlorinated Thienyl Conjugated Side Chains for High‐Performance Polymer Solar Cells via Toluene Processing

Small molecular acceptors (SMAs) BTC‐2F and BTH‐2F, based on heptacyclic benzodi(cyclopentadithiophene) electron‐donating core (CBT) with chlorinated‐thienyl conjugated and thienyl conjugated side chains, respectively, are designed and synthesized. Compared with non‐chlorine acceptor BTH‐2F, BTC‐2F exhibits slightly blue‐shifted absorption spectra, similar the lowest unoccupied molecular orbital (LUMO) (–3.91 eV), deeper highest occupied molecular orbital (HOMO) energy level and higher electron mobility than that of BTH‐2F. PM6, a wide bandgap polymer, is selected as the donor material to construct bulk heterojunction polymer solar cells processed with nonhalogenated solvent toluene. The optimized PM6:BTC‐2F‐based device presents a 12.9% power conversion efficiency (PCE), while the PCE of PM6:BTH‐2F‐based device is only 11.3%. The results suggest that it is an effective strategy to optimize the photoelectric properties of SMAs by incorporating chlorine atom into the conjugated side chains.     

Syntheses and Optoelectronic Properties of Planar Compounds 3,7‐diaryl‐1,5,2,4,6,8‐dithiotetrazocine

Planar molecules 3,7‐diaryl‐1,5,2,4,6,8‐dithiotetrazocines would be potential acceptor materials of organic solar cell because of their containing SN units. One‐pot synthetic procedures of 3,7‐diaryl‐1,5,2,4,6,8‐dithiotetrazocine compounds are developed to improve their yields up to 2.1–5.9 times as much as those in literatures. The geometries of title compounds were optimized by the density functional theory calculations. Their optoelectronic properties were studied by ultraviolet and cyclic voltammetry spectra and fluorescence quenching experiments. The highest occupied and lowest unoccupied molecular orbital energy level values show that these compounds are suitable to be employed as acceptor materials for developing bulk heterojunction organic solar cells with high open circuit voltages. Emission fluorescence of poly(3‐hexylthiophene) at excited state in dichloromethane was quenched by addition of title compound. Therefore, these compounds used as acceptor materials could exhibit good mobility.