Solution processable benzooxadiazole and benzothiadiazole based D-A-D molecules with chalcogenophene: field effect transistor study and structure property relationship

Synthesis of a Benzothiadiazole-Based D−A Molecule with Aggregation-Induced Emission and Controlled Assembly Properties

An electron-donating−accepting (D−A) molecule, namely, 4-(1-(4-(9H-carbazol-9-yl)phenyl)-1H-1,2,3-triazol-4-yl)benzo[c][1,2,5]thiadiazole (BT-SCC) containing carbazole as the donor moiety and benzothiadiazole as the acceptor moiety is prepared. Single-crystal X-ray structure analysis elucidated the multiple intermolecular interactions, such as hydrogen bonds, CH…π, and π…π interplays. Interestingly, the aggregation-induced emission phenomenon is observed for BT-SCC featured with enhanced fluorescent quantum yield from diluted solution of CH2Cl2 (Φ = ca. 0.1) to CH2Cl2/hexane mixed solutions or solid states (Φ = ca. 0.8). Finally, aggregates of BT-SCC are obtained through precipitating from hot and saturated solutions or solvent-vapor methods and the aggregating morphologies could be easily controlled through different preparation methods. Fabulous cube-like micro-crystals and nanospherical structures are obtained, which is established by the synergistic effects of the multiple non-covalent interactions, endowing potential utility in the field of optoelectronic devices.

Structural influence of a dichalcogenopheno-1,3,4-chalcogenodiazole comonomer on the optoelectronic properties of diketopyrrolopyrrole-based conjugated polymers

Dichalcogenopheno-1,3,4-chalcogenodiazole units are newly designed and introduced into dithienyl diketopyrrolopyrrole-based copolymers showing promising optoelectronic characteristics.

Defect-Passivating Organic/Inorganic Bicomponent Hole-Transport Layer for High Efficiency Metal-Halide Perovskite Device

In this work, we introduce a bicomponent hole-transport layer, composed of inorganic NiO_x and a donor-acceptor-donor (D-A-D)-structured organic small molecule, for p-i-n planar perovskite photovoltaic (PV) cells. The newly designed D-A-D organic hole-transporting material (HTM), (4',4‴-(1,3,4-oxadiazole-2,5-diyl)bis(N,N-bis(4-methoxyphenyl)-[1,1'-biphenyl]-4-amine)), is shown to be an efficient HTM without a dopant, and methoxy functional units, further introduced to the molecules, are confirmed to be beneficial to passivate the defects in the perovskite, which improves the crystallinity of perovskite and suppresses the nonradiative recombination in the devices, consequently enhancing the performances of PV cells (over 20% efficiency from p-i-n architecture). Furthermore, the decreased defect sites along with the UV-blocking property of the HTM in p-i-n architecture are advantageous in improving the stability of the PV devices.

The Prodigious Hydrogen Bonds with Sulfur and Selenium in Molecular Assemblies, Structural Biology, and Functional Materials

Hydrogen bonds (H-bonds) play important roles in imparting functionality to the basic molecules of life by stabilizing their structures and directing their interactions. Numerous studies have been devoted to understanding H-bonds involving highly electronegative atoms like nitrogen, oxygen, and halogens and consequences of those H-bonds in chemical reactions, catalysis, and structure and function of biomolecules; but the involvement of less electronegative atoms like sulfur and selenium in H-bond formation establishes the concept of noncanonical H-bonds. Initially belittled for the "weak" nature of their interactions, these perceptions have gradually evolved over time through dedicated efforts by several research groups. This has been facilitated by advancements in experimental methods for their detection through gas-phase laser spectroscopy and solution NMR spectroscopy, as well as through theoretical predictions from high level quantum chemical calculations.In this Account, we present insights into the versatility of the sulfur and selenium centered H-bonds (S/SeCHBs) by highlighting their multifarious applications in various fields from chemical reactions to optoelectronic properties to structural biology. Our group has highlighted the significance and strength of such H-bonds in natural and modified biomolecules. Here, we have reviewed several molecular assemblies, biomolecules, and functional materials, where the role of these H-bonds is pivotal in influencing biological functions. It is worth mentioning here that the precise experimental data obtained from gas-phase laser spectroscopy have contributed considerably to changing the existing perceptions toward S/SeCHBs. Thus, molecular beam experiments, though difficult to perform on smaller model thio- or seleno-substituted Molecules, etc. (amides, nucleobases, drug molecules), are inevitable to gather elementary knowledge and convincing concepts on S/SeCHBs that can be extended from a small four-atom sulfanyl dimer to a large 14 kDa iron-sulfur protein, ferredoxin. These H-bonds can also tailor a fascinating array of molecular frameworks and design supramolecular assemblies by inter- and intralinking of individual "molecular Lego-like" units.The discussion is indeed intriguing when it turns to the usage of S/SeCHBs in facile synthetic strategies like tuning regioselectivity in reactions, as well as invoking phenomena like dual phosphorescence and chemiluminescence. This is in addition to our investigations of the dispersive nature of the hydrogen bond between metal hydrides and sulfur or selenium as acceptor, which we anticipate would lead to progress in the areas of proton and hydride transfer, as well as force-field design. This Account demonstrates how ease of fabrication, enhanced efficiency, and alteration of physicochemical properties of several functional materials is facilitated owing to the presence of S/SeCHBs. Our efforts have been instrumental in the evaluation of various S/SeCHBs in flue gas capture, as well as design of organic energy harvesting materials, where dipole moment and polarizability have important roles to play. We hope this Account invokes newer perspectives with regard to how H-bonds with sulfur and selenium can be adequately adopted for crystal engineering, for more photo- and biophysical studies with different spectroscopic methods, and for developing next-generation field-effect transistors, batteries, superconductors, and organic thin-film transistors, among many other multifunctional materials for the future.

Benzoselenadiazole-Based Conjugated Molecules: Active Switching Layers with Nanofibrous Morphology for Nonvolatile Organic Resistive Memory Devices

In this work, two symmetrical donor-acceptor-donor (D-A-D) type benzoselenadiazole (BSeD)-based π-conjugated molecules were synthesized and employed as an active switching layer for non-volatile data storage applications. BSeD-based derivatives with different donor units attached through common vinylene linkers showed different electrical and optical properties. 4,7-Di((E)-styryl)benzo[c][2,1,3]selenadiazole (DSBSeD) and 4,7-bis((E)-4-methoxystyryl)benzo[c][2,1,3]selenadiazole (DMBSeD) are sandwiched between gallium-doped ZnO (GZO) and metal aluminum electrodes respectively through solution-processed spin-coating method. The solution-processed nanofibrous switching layer containing the DMBSeD-based memory device showed reliable memory characteristics in terms of write and erase operations with low SET voltage than the random-aggregated DSBSeD-based device. The nanofibrous molecular morphology of switching layer overcomes the interfacial hole transport energy barrier at the interface of the DMBSeD thin-film and the bottom GZO electrode. The memory device GZO/DMBSeD/Al based on nanofibrous switching layers shows switching characteristics at compliance current of 10 mA with V_set =0.79 V and V_reset =-0.55 V. This work will be beneficial for the rational design of advanced next-generation organic memory devices by controlling the nanostructured morphology of active organic switching layer for enhanced charge-transfer phenomenon.

Benzochalcogendiazole-based conjugated molecules: investigating the effects of substituents and heteroatom juggling

A convenient and effective synthetic approach for benzochalcogendiazole-based small molecules has been achieved using polyaniline (PANI)-anchored palladium as a heterogeneous catalyst. The photophysical properties of the synthesized benzochalcogendiazole-based small molecules, having different terminal substituents, have been compared. Moreover, the structural aspects, including the packing patterns and non-bonding interactions of the conjugated molecules, have been investigated using the single crystal X-ray diffraction (SCXRD) technique.

Effect of chalcogen atoms on the electronic band gaps of donor-acceptor-donor type semiconducting polymers: a systematic DFT investigation

We systematically investigated and compared the electronic band gaps of 16 different donor-acceptor-donor type semiconducting polymer systems that included different chalcogen atoms in their donor and acceptor units. The five-membered heterocyclic rings furan, thiophene, selenophene, and tellurophene were considered as electron donor units, whereas benzochalcogenadiazole groups, i.e., benzoxadiazole, benzothiadiazole, benzoselenadiazole, and benzotelluradiazole, were used as electron acceptor units. Our findings from B3LYP/6-31G(d) and B3LYP/LANL2DZ calculations performed with and without the polarizable continuum model indicated that the size of the chalcogen atom used as a heteroatom in the donor units plays a more important role than the size of the chalcogen atom in the benzochalcogenadiazole acceptor unit does. On the other hand, our results also suggest that the best way to modify and narrow the electronic band gap is to use heavy chalcogen atoms in both donor and acceptor units.

Effects of chalcogen atom variation in chalcogenadiazole fused indolo[2,3-a]carbazoles

The chalcogen (O/S/Se)-induced intriguing variation of structural and optoelectronic properties in a series of chalcogenadiazole-fused indolo[2,3-a]carbazole donor–acceptor (D–A) molecules.

Charge carrier mobility in one-dimensional aligned π-stacks of conjugated small molecules with a benzothiadiazole central unit

A theoretical study is applied to gain insight into the microscopic electron and hole transport in benzothiadiazole-cored molecular semiconductors either with furan or thiophene flanks arranged in π-stacks. For the characterization of the energetics of the reduction and oxidation processes and their impact on the molecular geometry, the internal reorganization energy is defined for isolated molecules in the gas phase. The outer-shell reorganization energy is evaluated within the frequency-resolved cavity model and as an electrostatic contribution within the polarizable continuum model. The intermolecular electronic coupling interaction for the Marcus charge hopping is calculated using the energy splitting in dimer method, the generalized Mulliken-Hush approach and the fragment charge difference scheme. In order to probe the relation between the charge hopping rate/charge carrier mobility and the molecular organization within the π-stacks, different stacking modes are investigated: (i) dimers with a perfect registry, i.e. segregated stacking motif, when molecules are placed face-to-face, and (ii) dimers forming slipped cofacial orientations with longitudinal and transverse shifts, i.e. mixed stacking motif. Besides, the effects of molecular planarity and rigidity, influencing internal molecular relaxation upon charging, the effects of non-covalent interactions within stacks and the heteroatom replacement on the charge carrier mobility are studied. The results obtained in the simulations of one-dimensional aligned π-stacks of molecular semiconductors are compared with available experimental data for small conjugated benzothiadiazole-cored molecules with thiophene flanks and benzothiadiazole-quaterthiophene-based copolymers.

Effect of heteroatom (S/Se) juggling in donor–acceptor–donor (D–A–D) fused systems: synthesis and electrochemical polymerization

Planarization of donor–acceptor–donor (D–A–D) systems through N-bridges with systematic alteration of S/Se atom(s) resulted in interesting fluorosolvatochromic molecules and their electrochemical polymers.

Selenium-Containing Fused Bicyclic Heterocycle Diselenolodiselenole: Field Effect Transistor Study and Structure-Property Relationship

The first application of the diselenolodiselenole (C4Se4) heterocycle as an active organic field effect transistor materials is demonstrated here. C4Se4 derivatives (2a-2d) were obtained by using a newly developed straightforward diselenocyclization protocol, which includes the reaction of diynes with selenium powder at elevated temperature. C4Se4 derivatives exhibit strong donor characteristics and planar structure (except 2d). The atomic force microscopic analysis and thin-film X-ray diffraction pattern of compounds 2a-2d indicated the formation of distinct crystalline films that contain large domains. A scanning electron microscopy study of compound 2b showed development of symmetrical grains with an average diameter of 150 nm. Interestingly, 2b exhibited superior hole mobility, approaching 0.027 cm(2) V(-1) s(-1) with a transconductance of 9.2 μS. This study correlate the effect of π-stacking, Se···Se intermolecular interaction, and planarity with the charge transport properties and performance in the field effect transistor devices. We have shown that the planarity in C4Se4 derivatives was achieved by varying the end groups attached to the C4Se4 core. In turn, optoelectronic properties can also be tuned for all these derivatives by end-group variation.

Effect of Selenium Substitution on Intersystem Crossing in π-Conjugated Donor-Acceptor-Donor Chromophores: The LUMO Matters the Most

This study explores the effect of substitution of selenium (Se) for sulfur (S) on the photophysical properties of a series of π-conjugated donor-acceptor-donor chromophores based on 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT). The effect of Se substitution is studied systematically, where the substitution is in the thiophene donors only, the benzothiadiazole acceptor only, and in all of the positions. The fluorescence quantum yield decreases with an increase in Se substitution. Nanosecond-microsecond transient absorption and singlet oxygen sensitization experiments show that the effect of Se is due to an increase in the rate and efficiency of intersystem crossing with increased Se substitution. The relationship between intersystem crossing efficiency and heteroatom substitution pattern shows that the effects are largest when the heavy atom Se is in the acceptor benzothiadiazole unit. DFT calculations support the hypothesis that the effect arises because the LUMO is concentrated in the acceptor moiety, enhancing the spin-orbit coupling effect imparted by the Se atom.

Branched and linear A2–D–A1–D–A2isoindigo-based solution-processable small molecules for organic field-effect transistors and solar cells

A₂–D–A₁–D–A₂type small molecules were synthesized, providing a solar cell efficiency of 1.9% and hole mobility of 3.7 × 10⁻³cm²V⁻¹s⁻¹.

Benzodipyrrolidone (BDP)-based polymer semiconductors containing a series of chalcogen atoms: comprehensive investigation of the effect of heteroaromatic blocks on intrinsic semiconducting properties

In order to determine the effects of actual 'chalcogen atoms' on semiconducting properties for application in a variety of optoelectronic devices, a class of donor (D)-acceptor (A) polymer semiconductors, namely PBDP-Fu, PBDP-Th, and PBDP-Se, containing the recently formulated benzodipyrrolidone (BDP) accepting unit and furan (Fu), thiophene (Th), or selenophene (Se) as a donating unit has been synthesized, characterized, and used in an active layer of organic field-effect transistors (OFETs). With the LUMO levels being comparatively consistent for all three polymers (-3.58 to -3.60 eV) due to the dominant BDP contribution to the polymer backbone, the HOMO energies are somewhat sensitive to the structurally distinctive feature of the donor counits used. Utilizing a combination of X-ray diffraction (XRD) and atomic force microscopy (AFM), it is apparent that further crystalline domains occur with edge-on orientation for the polymers (PBDP-Th and PBDP-Se) with relatively heavier chalcogen atoms such as Th and Se, compared with PBDP-Fu which has a rather amorphous nature. Investigation of their OFET performance indicates that all the polymers show well balanced ambipolar operations. The desirable morphological structures of both the PBDP-Th and PBDP-Se result in higher mobilities in OFETs than those of PBDP-Fu. In particular, 200 °C annealed PBDP-Se OFETs results in ambipolarity being mobile for both holes of up to 1.7 × 10(-2) cm(2)/V·s and electrodes of up to 1.9 × 10(-2) cm(2)/V·s. In addition, OFETs with PBDP-Th show nearly equivalent charge carrier mobilities for both holes (μ(h) = 1.2 × 10(-2) cm(2)/V·s) and electrons (μ(e) = 1.1 × 10(-2) cm(2)/V·s). Consequently, we systematically demonstrate how the manipulation of existing heteroaromatics can modulate the electronic properties of conjugated D-A polymers, elucidating structure-property relationships that are desirable for the rational design of next generation materials.