Lowest Unoccupied Molecular Orbital Energy Research Articles

Electronic levels of small molecules for organic solar cells: A computational study

Currently significant progress has been made for the small molecules, indeed, achieved comparable performance compared to polymer in electronic devices mainly due to the many advantages of small molecules over the polymers. Designing better small molecules for electronic applications are required a comprehensive understanding of the structure-properties relationship and the factors affecting it. Valuable information can be generated directly toward understanding by systematically theoretical and experimental studies (band gap, HOMO, LUMO energy levels and geometry). Hybrid density functional B3LYP level of theory is a very good method for predicting the reliable geometry, electronic structure and properties of conjugated systems. In the present work, we have calculated the band gaps, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and geometry of a series of small molecules based on oligothiophene, benzodithiophene and dithienosilole unit using the hybrid density functional (B3LYP/6-31G(d)) level of theory and correlated with experimental values. The study provides details for the effect of the extended conjugation, two-dimension conjugation, substitution on geometry, HOMO, LUMO and band gaps of the small molecules. Copyright © 2017 VBRI Press.

Designing New Indene-Fullerene Derivatives as Electron-Transporting Materials for Flexible Perovskite Solar Cells.

The synthesis and characterization of a family of indene-C60 adducts obtained via Diels–Alder cycloaddition [4 + 2] are reported. The new C60 derivatives include indenes with a variety of functional groups. These adducts show lowest unoccupied molecular orbital energy levels to be at the right position to consider these compounds as electron-transporting materials for planar heterojunction perovskite solar cells. Selected derivatives were applied into inverted (p–i–n configuration) perovskite device architectures, fabricated on flexible polymer substrates, with large active areas (1 cm2). The highest power conversion efficiency, reaching 13.61%, was obtained for the 6′-acetamido-1′,4′-dihydro-naphtho[2′,3′:1,2][5,6]fullerene-C60 (NHAc-ICMA). Spectroscopic characterization was applied to visualize possible passivation effects of the perovskite’s surface induced by these adducts.

Effects of Halogenation on the Benzotriazole Unit of Non-Fullerene Acceptors in Organic Solar Cells with High Voltages.

Non-fullerene acceptors (NFAs) can be simply divided into three categories: A-D-A, A-DA'D-A, and A2-A1-D-A1-A2 according to their chemical structures. Benefiting from the easily modified 1,1-dicyanomethylene-3-indanone end groups, the halogenation on the first two types of materials has been proved to be very effective to modulate their optoelectronic properties and improve their photovoltaic performance. Hence, in this work, we systematically investigate the effect of halogenation on the classic NFA molecule of BTA3, which has the linear A2-A1-D-A1-A2-type backbone. After fluorination and chlorination, F-BTA3 and Cl-BTA3 have similar optical band gaps but lower energy levels than BTA3. When blending with a linear copolymer PE25 composed of benzodifuran and chlorinated benzotriazole (BTA) according to "Same-A-Strategy", the corresponding VOC of the halogenated NFAs gradually decreases (1.13 V for F-BTA3 and 1.09 V for Cl-BTA3), compared with that of the BTA3-based device (VOC = 1.22 V). This tendency mainly comes from the lower lowest unoccupied molecular orbital energy levels due to the strong electron-withdrawing ability of halogen atoms and the larger nonradiative energy loss. However, the power conversion efficiencies of the halogenated materials are slightly improved, from 9.08% for PE25: BTA3 to 10.45% for PE25: F-BTA3 and 10.75% for PE25: Cl-BTA, with the nonhalogenated solvent tetrahydrofuran as the processing solvent. The improved photovoltaic performance of F-BTA3 and Cl-BTA3 should come from the higher carrier mobility, weaker bimolecular recombination, and higher fluorescence quenching rate. This study illustrates that halogenation on the A1 unit is a promising strategy for developing novel and effective A2-A1-D-A1-A2-type NFAs.

The Influence of Anion Structure on the Ionic Liquids/Au (100) Interface by Molecular Dynamics Simulations.

The microstructure of electrical double layers (EDLs) of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-butyl-3-methylimidazoliumhexafluorophosphate ([Bmim]PF6), and 1-butyl-3-methylimidazoliumbis (trifluoromethylsulfonyl) imide ([Bmim]TFSI) were studied by quantum chemical calculation and molecular dynamics simulation. For the set of ionic liquids investigated here, we found some interesting universal laws due to differences geometry and electronic structure of anions. We show that the morphology of the three anions on the electrode surface is different due to the different geometric structure. The plane formed by the bottom three atoms of the symmetrically tetrahedral BF4- and the bottom atom of the symmetrically octahedral PF6- face the electrode whether the electrode is charged or not, while the conformation of twisted V-shaped TFSI- changes with different surface charges on the electrode. Meanwhile, we also demonstrate that the energy of highest occupied molecular orbital (EHOMO), the energy of lowest unoccupied molecular orbital (ELUMO) and their energies gap (ΔE) are very interesting due to different electronic structure of anions. Specially, the EHOMO, ELUMO, and ΔE were related to the electronegativity of the central atom in the case of the same symmetry on the neutral surface. The more electronegative the central atom is, the lower EHOMO, ELUMO and higher ΔE values are. However, on the charged surface, the interaction between anion and electrode is opposite to ΔE. Moreover, different arrangements of anion and cation are related to the interaction between particles. The stronger interaction leads a double-row structure and the weak interaction lead worm-like and island patterns on Au (100) surface. In general, we observed that the higher ΔE cause stronger interaction, which lead to different patterns on Au (100) surface. Meanwhile, we also confirmed that the stronger interaction between particles and electrode lead to the thinner effective EDL and a large differential capacitance value. These results provide a new perspective for double-layer structure in atomic and molecular level. This is helpful to deepen the understanding of the interface phenomena and characteristics of [Bmim]BF4, [Bmim]PF6, and [Bmim]TFSI on Au (100) system and provide theoretical basis for the application of these kind of systems.

Experimental and computational investigation on spectroscopic characterization, molecular modeling and biological evaluation of 3, 3′, 4′7-tetrahydroxyflavone, 3, 3′, 4′7-tetrahydroxyflavone-6-methoxymethane against in A549 cells

The Molecular structural, vibrational, frequencies electronic and potential energy distribution of 3, 3′ , 4′7-tetrahydroxyflavone and 3′, 4′7-tetrahydroxyflavone-6-methoxymethane molecules have been carried out using the techniques of FT-IR and FT-Raman spectra with the aid of computational calculations and compared with experimental calculations. The electronic properties, such as highest occupied molecular orbital and the lowest unoccupied molecular orbital energy levels, molecular electrostatic potential and atomic charges analysis were performed at above levels. The correlation graphs of observed versus calculated vibrational frequencies were plotted and density functional theory gave better wavenumber agreement than others. Molecular docking study show that the intermolecular hydrogen-bonding interactions and binding free energy of -8.4 kcal/mol and -8.1 kcal/mol between 3THDFN and 6THDFN with 1AO6 protein were reported and this study supported the in designing structure-based Human Serum Albumin (HSA) receptors may be of significant biological and pharmaceutical importance. In additional, the in vitro cytotoxicity of compounds confirms the anticancer activity against human lung cancer cell lines was assessed in 24-h tetrazoliumbromide-dye (MTT) cytotoxicity assays. Hence, the present investigations pave the way for the development of lung cancer drugs (A549).

Evaluation of Computational Chemistry Methods for Predicting Redox Potentials of Quinone-Based Cathodes for Li-Ion Batteries

High-throughput computational screening (HTCS) is an effective tool to accelerate the discovery of active materials for Li-ion batteries. For the evaluation of organic cathode materials, the effectiveness of HTCS depends on the accuracy of the employed chemical descriptors and their computing cost. This work was focused on evaluating the performance of computational chemistry methods, including semi-empirical quantum mechanics (SEQM), density-functional tight-binding (DFTB), and density functional theory (DFT), for the prediction of the redox potentials of quinone-based cathode materials for Li-ion batteries. In addition, we evaluated the accuracy of three energy-related descriptors: (1) the redox reaction energy, (2) the lowest unoccupied molecular orbital (LUMO) energy of reactant molecules, and (3) the highest occupied molecular orbital (HOMO) energy of lithiated product molecules. Among them, the LUMO energy of the reactant compounds, regardless of the level of theory used for its calculation, showed the best performance as a descriptor for the prediction of experimental redox potentials. This finding contrasts with our earlier results on the calculation of quinone redox potentials in aqueous media for redox flow batteries, for which the redox reaction energy was the best descriptor. Furthermore, the combination of geometry optimization using low-level methods (e.g., SEQM or DFTB) followed by energy calculation with DFT yielded accuracy as good as the full optimization of geometry using the DFT calculations. Thus, the proposed calculation scheme is useful for both the optimum use of computational resources and the systematic generation of robust calculation data on quinone-based cathode compounds for the training of data-driven material discovery models.

Aggregation-Induced Fluorogens in Bio-Detection, Tumor Imaging, and Therapy: A Review

Aggregation-Induced Fluorogens in Bio-Detection, Tumor Imaging, and Therapy: A Review

Electronic and Optical Properties of Polythiophene Molecules and Derivatives

The electronic and optical properties of polythiophene (PT) for polymer light-emitting diodes (PLEDs) were calculated using density functional theory (DFT) and time-dependent DFT. We calculated the electronic and optical properties of thiophene and PT polymers with degrees of polymerization (DP) from 2 to 30 monomers (T1–T30) and their derivatives. The associated highest occupied molecular orbital (HOMO) energy, lowest unoccupied molecular orbital (LUMO) energy, band gaps, electron orbitals, and molecular structures were determined. As the DP increased, the LUMO energy gradually decreased, and the HOMO energy gradually increased. The band gap of PT approached 2 eV as the DP of the PT polymer increased from 1 to 30. The calculations and exchange–correlation functional were verified against values in the literature and experimental data from cyclic voltammetry (redox potential) and ultraviolet-visible, photoluminescence, and ultraviolet photoelectron spectra. The color of PT PLEDs can be adjusted by controlling the DP of the polymer and the substituents.

Quantum Chemical Analysis of the Corrosion Inhibition Potential by Aliphatic Amines.

Destructive corrosion processes lead to the loss of primary mechanical properties of metal construction materials, which generates additional costs during their maintenance connected with repairs and protection. The effectiveness of corrosion inhibitors can be determined by using many methods, in particular quantum chemical modeling. The subject of the theoretical analyses presented in this work involves the anticorrosion properties of amines with various chemical structures. Evaluation of the corrosion inhibition properties of selected amines was performed on the basis of the HOMO–LUMO energy gap, dipole moment (µ), electronegativity (χ) determined as a result of the energy of the highest occupied molecular orbital (HOMO) and the energy of the lowest unoccupied molecular orbital (LUMO). Moreover, the HSAB (Hard and Soft Acids and Bases) theory was used to explain the reactivity of the analyzed amines, while the Mulliken population analysis was used to determine their electrostatic interactions with the surface of protected metal. The obtained results indicate that the protonation reaction of aliphatic amines leads to a change in the nature of the formation of a coordination bond with the surface of the protected metal. In turn, the quantum chemical calculations showed that the protonation reaction of aliphatic amines leads to a decrease in their corrosion inhibition efficiency. Most of the analyzed parameters indicated that tertiary amines are characterized by the highest corrosion inhibition efficiency.

Solution-processable silicon naphthalocyanine tetraimides as near infrared electron acceptors in organic solar cells

Two silicon naphthalocyanine electron acceptors, CH3O-SiNcTI and 3BSO-SiNcTI, with four strong electron-withdrawing imide groups, were designed, synthesized, and applied in bulk heterojunction organic solar cells (BHJ OSCs). They exhibited strong near-infrared absorption in 300–1100 nm, maximum extinction coefficients of up to 5.2 × 105 M−1 cm−1, deep lowest unoccupied molecular orbital energy levels of −3.92 eV, and good photothermal stability. The power conversion efficiency of BHJ OSCs based on acceptor of 3BSO-SiNcTI reached 4.22%, which is the highest value among solution-processable phthalocyanine or naphthalocyanine derivatives. The measurements of space-charge-limited current, charge recombination, charge collection capability, atomic force microscopy (AFM), and transmission electron microscopy (TEM) were carried out. It is found that BHJ OSCs based on PTB7-Th:3BSO-SiNcTI, have higher and balanced carrier mobility, less charge recombination, better charge transport, and favorable film morphology, which lead to their higher photovoltaic performance. This study indicates the great potential of SiNcTIs as near-infrared chromophores for high-performance electron acceptors in BHJ OSCs.

Computational Methods and Molecular Modelling for Some Predicted Tautomers of Pyrimidine Compounds

Introduction: Several molecular modelling techniques and quantum chemical methods have been performed to correlate the chemical structures of the compounds with their physical molecular properties. Methods: Using theoretical parameters help to characterize the molecular structure of the investigated ligands and to study their equlibria mechanism. Molecular modelling data such as the bond length, bond order, bond angles and dihedral angles values were estimated for some pyrimidine compounds, where the data suggested the presence of tautomerism and a dynamic equilibria are deduced between all the detected tautomers in the solid state. Results: Four main tautomers were predicted for barbital and thiobarbituric acid, while three tautomers were for thiouracil. Quantum chemical parameters such as the highest occupied molecular orbital energy (EHOMO), the lowest unoccupied molecular orbital energy (ELUMO), energy gap (ΔE), dipole moment (μ), sum of the total negative charge (STNC), electronegativity (χ), chemical potential (Pi), global hardness (η) and softness (σ) were calculated. Conclusion: These studies display a good correlation between the theoretical and experimental data.

Insight into Anticorrosion Mechanism of Ampicillin on Mild Steel in Acidic Environment: A Combined Experimental and Theoretical Approach

The corrosion inhibition of mild carbon steels in an acidic environment by using ampicillin (AMP) has been evaluated based on experimental and quantum chemistry techniques. The experimental results indicate that the inhibition efficiency goes up at higher AMP concentration. The highest inhibition efficiency reaches 84.9% for polarization measurement and 90.1% for electrochemical impedance spectroscopy with the inhibitor of concentration 100 ppm at 298 K. The surface characteristics (SEM) also reconfirm the steel corrosion inhibition ability of AMP. Some important chemical factors such as EHOMO (highest occupied molecular orbital energy), ELUMO (lowest unoccupied molecular orbital energy), ΔEL−H (energy gap), and Fukui functions were calculated based on the optimized configuration of AMP at the theoretical level of B3LYP/6-31+G(d,p). Moreover, Monte Carlo and molecular dynamics simulations were used to analyze the absorption behavior of inhibitor on the surface of Fe(110), which supplies the mechanism of inhibition corrosion processes. The obtained results showed that AMP is considered to be a potential corrosion inhibitor for mild steel in 1M HCl medium. Moreover, the protonated state of AMP plays an important role in the protection of Fe surface against the corrosive process.

Facile synthesis of aminoalkyl naphthols and single crystal X-ray, computational studies on 1-[morpholino(thiophen-2-yl)methyl]naphthalen-2-ol

• One-pot, three-component organic synthesis. • Single crystal XRD confirms the formation of compound. • Crystalized compound compared with the theoretical calculation of DFT. • The HOMO–LUMO energy gap reveals the chemical stability of the compound. An efficient, eco-friendly protocol is developed for the synthesis of 1- (α-aminoalkyl)-2-naphthol derivatives via one-pot three-component reaction of 2-naphthol, aromatic aldehydes and piperidine or morpholine in the presence of Amberlite IRA-400 Cl resin as a catalyst. This approach carries characteristics of one-pot synthesis, high yield, and mild, clean reaction conditions with the recyclable catalyst. One of the products ( 4p ), crystalized in trigonal crystal system with P32 space group, was obtained and compared with the theoretical calculation of popular Density Functional Theory (DFT), B3LYP/6-311++G(d,p) basis set. The energy of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) was calculated. All theoretical calculations agree with the experimental values.

A Y6-based polymerized small-molecule acceptor with non-conjugated alkyl linkages for efficient all-polymer solar cells

A polymerized small-molecule acceptor, NC-PY6, has been newly designed and successfully synthesized. NC-PY6 contains a rigid conjugated Y6-derived fused-ring small acceptor SY6 and a non-conjugated alkyl chain as the linkage. Similar to SY6, NC-PY6 exhibits the narrow bandgap of 1.44 eV and the low-lying lowest unoccupied molecular orbital energy level (−3.92 eV), which match with the known wide-bandgap polymer donor D18. The D18:SY6 based polymer solar cells showed a power conversion efficiency (PCE) of 13.1% with a voltage loss of 0.58 V. The all-polymer solar cells (all-PSCs) based on D18:NC-PY6 blend film gave an encouraging PCE of 12.3% with a voltage loss of 0.57 V. The results demonstrate the potential of molecular design strategy of polymerizing small-molecule acceptor with the non-conjugated alkyl chain as the linkage for new type of polymer acceptors for high-performance all-PSCs.

Fine‐Tuning the Photovoltaic Performance of Organic Solar Cells by Collaborative Optimization of Structural Isomerism and Halogen Atom

Fused‐ring acceptors based on an electron‐deficient core, such as Y6, have become a successful strategy in bulk heterojunction (BHJ) organic solar cells (OSCs) for high power conversion efficiencies (PCEs). Here, five fused‐ring electron acceptors (Y9, Y9‐2F, Y9‐2Cl, i‐Y9‐2F, i‐Y9‐2Cl) are synthesized using fused dithienothiophen[3,2‐b]pyrrolobenzotriazole and halogenated 1,1‐dicyanomethylene‐3‐indanone (IC) to investigate the effect of end‐group (EG) halogenation and structural isomerism on BHJ photovoltaic performance. Due to the strong electronegativity of halogens, all the acceptors with halogenated terminal units possess redshifted absorption spectra and deeper frontier energy levels compared with Y9. Different from asymmetric molecules i‐Y9‐2F and i‐Y9‐2Cl, Y9‐2F and Y9‐2Cl exhibit slightly lower bandgaps. Moreover, the devices based on fluorinated acceptors show more efficient charge collection, obtaining relatively high short‐circuit current density (J sc) and fill factor (FF). The lowest unoccupied molecular orbital energy levels of halogenated acceptors are similar. As a result, OSCs based on poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithio‐phene))‐alt‐(5,5‐ (1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethyl‐hexyl) benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))] (PBDB‐T):Y9‐2F obtain more balanced J sc and open‐circuit voltage (V oc), and thus an optimal PCE of 15.49% is demonstrated with a V oc of 0.84 V, J sc of 26.30 mA cm−2, and FF of 70.05%.

A Convenient DFT-Based Strategy for Predicting Transition Temperatures of Valence Tautomeric Molecular Switches.

The ability to identify promising candidate switchable molecules computationally, prior to synthesis, represents a considerable advance in the development of switchable molecular materials. Even more useful would be the possibility of predicting the switching temperature. Cobalt-dioxolene complexes can exhibit thermally induced valence tautomeric switching between low-spin CoIII-catecholate and high-spin CoII-semiquinonate forms, where the half-temperature (T1/2) is the temperature at which there are equal amounts of the two tautomers. We report the first simple computational strategy for accurately predicting T1/2 values for valence tautomeric complexes. Dispersion-corrected density functional theory (DFT) methods have been applied to the [Co(dbdiox)(dbsq)(N2L)] (dbdiox/dbsq•- = 3,5-di-tert-butyldioxolene/semiquinonate; N2L = diimine) family of valence tautomeric complexes, including the newly reported [Co(dbdiox)(dbsq)(MeO-bpy)] (1) (MeO-bpy = 4,4'-dimethoxy-2,2'-bipyridine). The DFT strategy has been thoroughly benchmarked to experimental data, affording highly accurate spin-distributions and an excellent energy match between experimental and calculated spin-states. Detailed orbital analysis of the [Co(dbdiox)(dbsq)(N2L)] complexes has revealed that the diimine ligand tunes the T1/2 value primarily through π-acceptance. We have established an excellent correlation between experimental T1/2(toluene) values for [Co(dbdiox)(dbsq)(N2L)] complexes and the calculated lowest unoccupied molecular orbital energy of the corresponding diimine ligand. The model affords accurate T1/2(toluene) values for [Co(dbdiox)(dbsq)(N2L)] complexes, with an average error of only 3.7%. This quantitative and simple DFT strategy allows experimentalists to not only rapidly identify proposed VT complexes but also predict the transition temperature. This study lays the groundwork for future in silico screening of candidate switchable molecules prior to experimental investigation, with associated time, cost, and environmental benefits.

DFT/TDDFT Investigation on donor-acceptor triazole-based copolymers for organic photovoltaics

Using density functional theory (DFT) method, we studied several triazole-based donor-acceptor (DA) π-conjugated molecules and evaluated their lowest unoccupied molecular orbital (LUMO) energies. Our results shows that bithiophene-substituted triazole-based acceptors with short and non-bulky substituents tend to be co-planar and hence exhibit stronger conjugation and electron delocalization, thereby leading to lower orbital energies of LUMO. Introduction of heteroatom such as S and Se within the chemical structure of triazole-based acceptor also significantly reduces the bandgap by lowering the LUMO energies. Among the donor fragments studied, a dithieno [3,2-b:2′,3′-d]phosphole donor fragment (Y4) led to donor-acceptor (DA) pairs with comparatively lower highest occupied molecular orbitals (HOMO, (-5.01 to -4.69 eV) along with higher VOC (>1.29 eV) without much compromise in its bandgap energy. This makes such DA-based polymers promising for bulk heterojunction solar cell applications. TD-DFT calculations were further used to simulate the absorption spectra of the DA monomers and showed that most pairs gave meaningful absorption from 400 to 1100 nm. More interestingly, the addition of long aromatic substituents in the acceptor fragment tends to give broader absorption spectra. Further studies on trimers with DDA repeating unit revealed that copolymers bearing Y4 and a benzo [1,2-d;4,5-d’]bitriazole X1 (or X6) exhibits close to ideal band gap of 1.37 eV (1.36 eV) with favorable open circuit voltage 1.23 eV, though absorption by Y4-Y4-X1 takes place in Infrared scope with higher oscillator strength. All in all, we identified a polymer comprising Y4 donor and X1 acceptor fragment to be a promising material for heterojunction organic solar cell application.

Harnessing the Inductive Effect To Design New Donor–Acceptor–Acceptor′-Configured Small-Molecule Donors for Vacuum-Processed Organic Photovoltaics

Three new donor–acceptor–acceptor′ (D–A–A′)-configured molecules, DTCFiBT, DTCFoBT, and DTCF2BT, with F-substituted benzothiadiazole (BT) as the A group, and two molecules, DTCPiTD and DTCPoTD, adopting pyridal[2,1,3]-thiadiazole (PTD) as the A group, were synthesized and characterized. The effects of the F-substitution number and the orientation of mono F-substituted BT and PTD relative to the D group on the physical properties and intermolecular interactions were examined, together with theoretical calculations to establish the structure–property relationship. In comparison to the parent molecule DTCPB, the inductive effects of F-substituted BTs lower both highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of DTCFiBT, DTCFoBT, and DTCF2BT and, thus, similar optical energy gaps (Egopt), while DTCPiTD and DTCPoTD exhibit much lower LUMO energy levels and reduced Egopt, ascribing to the electron-deficient character of PTD. The strong dipolar features of the D–A–A′-configured structure resulting in the antiparallel dimeric packing with different intermolecular interactions in their crystal structures were observed by X-ray analyses. Small-molecule organic solar cells (SMOSCs) with a bulk heterojunction active layer comprising new D–A–A′ donors and C70 were fabricated and characterized. The deeper LUMO levels and reduced Egopt benefit the DTCPiTD- and DTCPoTD-based devices to have higher short current density (JSC), while the DTCFiBT-, DTCFoBT-, and DTCF2BT-based devices benefited from the lower HOMO energy levels that lead to the higher open circuit voltage (VOC). Transient photoluminescence, atomic force microscopy, and incident-light-intensity-dependent device characteristics were examined to reveal the recombination issue for the inferior DTCFoBT-based device. Among these new donors, the DTCFiBT-based device shows the best performance, with VOC of 0.94, JSC of 11.3 mA/cm2, fill factor (FF) of 0.65, and power conversion efficiency of 6.8%, which are attributed to the high VOC as a result of the deeper HOMO level and the superior FF as a result of good exciton separation and charge carrier transport.

Nematic and smectic bithiophenes for UV sensing mechanism: Comparative calculations on different homologues

Four liquid crystalline molecules in the homologus series of 5,5′-Bis-(alkylpyridinyl)-2,2′-bithiophenes (nPBTP with n = 7, 8, 10, 12) have been investigated for UV sensing mechanism. Optimization of these compounds has been carried out through hybrid functional B3LYP along with 6-31 + G (d) basis set based on the crystallographic parameters as input. The UV absorption spectra of the molecules have been calculated and the configuration interaction singles (CIS) approach has been employed to study the electronic transitions features along with excited states calculation with the help of semiempirical Hamiltonian ZINDO. The INDO/S + CI method has been implemented for the same for comparison of the results. Various spectral parameters associated have been reported. The HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies estimations, and the transition energies, the electron excitation nature concerning on the structural variations in the molecules are clarified. The results obtained suggest model UV sensing mechanism for full colour display applications. A comparison has been made between nematic and smectic systems.

Structure–property relationship of donor–acceptor type conjugated copolymers with thienoisoquinoline and benzothiadiazole units

We synthesized a new series of donor–acceptor (D-A) type conjugated copolymers containing two electron-accepting units, namely thienoisoquinoline (TIQO) and benzothiadiazole (BT) (PTIQO-HBT) or fluorinated BT analogs (PTIQO-FBT and PTIQO-FFBT) connected to thiophene-based electron-donating units. The optical and electrochemical properties, planarity of conjugated backbone, molecular crystalline structure, and charge transport characteristics were investigated to comprehensively study the structure–property relationship of these semiconducting copolymers. When the BT unit carries 0, 1, and 2 fluorine, both the highest occupied and the lowest unoccupied molecular orbital energy levels of the conjugated copolymers gradually decrease. DFT calculations showed no significant difference in the energy gap or the copolymer backbone planarity. However, the grazing incidence X-ray diffraction results confirm that the PTIQO-FBT copolymer film has a longer coherence length of π–π stacking between the molecular chains than PTIQO-HBT and PTIQO-FFBT, which may affect the intermolecular charge transport. Organic field-effect transistors (OFETs) employing the three TIQO-based D-A type semiconductor copolymer films as active layer all exhibited ambipolar characteristics that enable both hole and electron transport. Particularly, the PTIQO-FBT based OFETs (hole mobility: 0.030 cm2/V·s, electron mobility: 0.023 cm2/V·s) demonstrate higher performance with well-balanced hole and electron transport, as compared to the other two copolymers in terms of field-effect mobility. Therefore, introducing a single fluorine into the BT unit in the TIQO-based D-A type conjugated copolymers results in the most appropriately controlled ground-state charge transfer for efficient intramolecular charge transport along the polymer backbone, as well as higher molecular film crystallinity.