Intermolecular H···O═C bonds induced 2D self‐assembly of thiophene based diketopyrrolopyrrole derivative

Compounds with diketopyrrolopyrrole (DPP) and thiophene moieties have attracted considerable attention because of their promising charge transport properties. The molecular conformation and self‐assembly of 2,5‐dihexadecyl‐3,6‐di(thiophen‐2‐yl)‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione (TDPP‐C16) molecule have been investigated by scanning tunneling microscopy and density functional theory alculation. The TDPP‐C16 molecules adsorb with their optimized S‐shaped conformation and form a zipper‐like pattern on highly oriented pyrolytic graphite surface. R and S rotated structures are observed. The nanostructure is dominated by intermolecular double hydrogen bonds between C═O of the DPP units and hydrogen atom of thiophene rings in the neighboring molecules in each row. Atomic force microscopy and density functional theory calculation also display the existence of strong intermolecular hydrogen bonding. The results provide molecular evidence for the intermolecular interactions of the surface structure, which could benefit to the design of the organic semiconducting materials and understanding of underlying principle of charge transfer process. Copyright © 2017 John Wiley & Sons, Ltd.     

Electronic structure and microscopic charge‐transport properties of a new‐type diketopyrrolopyrrole‐based material

Recently, diketopyrrolopyrrole (DPP)‐based materials have attracted much interest due to their promising performance as a subunit in organic field effect transistors. Using density functional theory and charge‐transport models, we investigated the electronic structure and microscopic charge transport properties of the cyanated bithiophene‐functionalized DPP molecule (compound 1 ). First, we analyzed in detail the partition of the total relaxation (polaron) energy into the contributions from each vibrational mode and the influence of bond‐parameter variations on the local electron–vibration coupling of compound 1 , which well explains the effects of different functional groups on internal reorganization energy (λ). Then, we investigated the structural and electronic properties of compound 1 in its isolated molecular state and in the solid state form, and further simulated the angular resolution anisotropic mobility for both electron‐ and hole‐transport using two different simulation methods: (i) the mobility orientation function proposed in our previous studies (method 1); and (ii) the master equation approach (method 2). The calculated electron‐transfer mobility (0.00003–0.784 cm² V^?1 s^?1 from method 1 and 0.02–2.26 cm² V^?1 s^?1 from method 2) matched reasonably with the experimentally reported value (0.07–0.55 cm² V^?1 s^?1). To the best of our knowledge, this is the first time that the transport parameters of compound 1 were calculated in the context of band model and hopping models, and both calculation results suggest that the intrinsic hole mobility is higher than the corresponding intrinsic electron mobility. Our calculation results here will be instructive to further explore the potential of other higher DPP‐containing quinoidal small molecules. © 2015 Wiley Periodicals, Inc.     

吡咯并吡咯二酮与低聚噻吩共聚物电荷传输性质的理论研究

利用密度泛函理论对吡咯并吡咯二酮(DPP)与噻吩形成共聚物的低聚物(PDPP-n T)m的电子结构及二体堆积模型的电荷传输性质进行计算.结果表明,随着聚合物单元内DPP浓度增加,噻吩数减少,聚合物分子的HOMO和LUMO能级同时降低,并且HOMO-LUMO带隙变小;链内相邻DPP单元的电子波函数有效重叠增大,显著改善了链内的电子传输能力;同时分子主链的刚性增强,使分子链间LUMO轨道重叠增强,电子转移积分增大;最终体系由p型向双极性材料转化.     

Influence of Backbone Chlorination on the Electronic Properties of Diketopyrrolopyrrole (DPP)‐Based Dimers

Chlorination of π‐conjugated backbones is garnering great interest because of fine‐tuning electronic properties of conjugated materials for organic devices. Herein we report a synthesis of thiophene‐based diketopyrrolopyrrole (DPP) dimers and their chlorinated counterparts by introducing a chlorine atom in the outer thiophene ring to investigate the influence of the chlorination on charge transport. The backbone chlorination lowers both the HOMO and the LUMO of the dimers and leads to a blue‐shift of maximum absorption in compared to unsubstituted counterparts. X‐ray analysis reveals that the chlorine atom prompts the outer thiophene ring out of the planarity of the backbone with a relatively large torsional angle. The chlorinated dimers exhibit slipped one‐dimensional packing decorated with multiple intermolecular interactions, because of a combination of a negative inductive effect and a positive mesomeric effect of the halogen atom, which might facilitate charge transport within the oligomeric backbones. The mobility in the single‐crystal OFET devices of the chlorinated dimers is up to 1.5 cm² V^?1 s^?1, which is two times higher than that of the non‐chlorinated DPP dimers. Our results indicate that the chlorine atom plays a key role in directing non‐covalent interactions to lock the slipped stacks, enabling electronic coupling between adjacent molecules for efficient charge transport. In addition, our results also demonstrate that these DPP dimers with straight n‐octyl chains exhibit higher mobilities than the dimers with branched 2‐ethylhexyl chains.     

Rational Design of Star-shaped Molecules with Benzene Core and Naphthalimide Derivatives End Groups as Organic Light-emitting Materials

A series of star-shaped molecules with benzene core and naphthalimides derivatives end groups have been designed to explore their optical,electronic,and charge transport properties as charge transport and/or luminescent materials for organic light-emitting diodes(OLEDs). The frontier molecular orbitals(FMOs) analysis has turned out that the vertical electronic transitions of absorption and emission are characterized as intramolecular charge transfer(ICT). The calculated results show that the optical and electronic properties of star-shaped molecules are affected by the substituent groups in N-position of 1,8-naphthalimide ring. Our results suggest that star-shaped molecules with n-butyl(1),benzene(2),thiophene(3),thiophene S?,S?-dioxide(4),benzo[c][1,2,5]thiadiazole(5),and 2,7a-dihydrobenzo[d]thiazole(6) fragments are expected to be promising candidates for luminescent and electron transport materials for OLEDs. This study should be helpful in further theoretical investigations on such kind of systems and also to the experimental study for charge transport and/or luminescent materials for OLEDs.     

Selective inclusion of electron-donating molecules into porphyrin nanochannels derived from the self-assembly of saddle-distorted, protonated porphyrins and photoinduced electron transfer from guest molecules to porphyrin dications

A doubly protonated hydrochloride salt of a saddle-distorted dodecaphenylporphyrin (H2DPP), [H4DPPP]Cl2, forms a porphyrin nanochannel (PNC). X-ray crystallography was used to determine the structure of the molecule, which revealed the inclusion of guest molecules within the PNC. Electron-donating molecules, such as p-hydroquinone and p-xylene, were selectively included within the PNC in sharp contrast to electron acceptors, such as the corresponding quinones, which were not encapsulated. This result indicates that the PNC can recognize the electronic character and steric hindrance of the guest molecules during the course of inclusion. ESR measurements (photoirradiation at lambda>340 nm at room temperature) of the PNC that contains p-hydroquinone, catechol, and tetrafluorohydroquinone guest molecules gave well-resolved signals, which were assigned to cation radicals formed without deprotonation based on results from computer simulations of the ESR spectra and density functional theory (DFT) calculations. The radicals are derived from photoinduced electron transfer from the guest molecules to the singlet state of H4DPP2+. Transient absorption spectroscopy by femtosecond laser flash photolysis allowed us to observe the formation of 1(H4DPP2+)*, which is converted to H4DPP+. by electron transfer from the guest molecules to 1(H4DPP2+)*, followed by fast disproportionation of H4DPP+., and charge recombination to give diamagnetic species and the triplet excited state 3(H4DPP2+)*, respectively.     

Properties of Sizeable [n]Cycloparaphenylenes as Molecular Models of Single‐Wall Carbon Nanotubes Elucidated by Raman Spectroscopy: Structural and Electron‐Transfer Responses under Mechanical Stress

[n]Cycloparaphenylenes behave as molecular templates of “perfectly chemically defined” single‐wall carbon nanotubes. These [n]CPP molecules have electronic, mechanical, and chemical properties in size correspondence with their giant congeners. Under mechanical stress, they form charge‐transfer salts, or complexes with fullerene, by one‐electron concave–convex electron transfer.     

Diketopyrrolopyrrole?Thiophene‐Based Acceptor–Donor–Acceptor Conjugated Materials for High‐Performance Field‐Effect Transistors

We report the synthesis, morphology, and field‐effect‐transistor (FET) characteristics of new acceptor–donor–acceptor conjugated materials that consist of diketopyrrolopyrrole (DPP) acceptor groups and one of four different thiophene moieties, that is, dithiophene (2T), thieno[3,2‐b]‐thiophene (TT), dithieno[3,2‐b:2′,3′‐d]‐thiophene (DTT), and 5,5′′′‐di‐(2‐ethylhexyl)‐[2,3′;5′,2′′;4′′,2′′′]quaterthiophene (4T). The optical band gaps of the as‐prepared materials are smaller than 1.7 eV, which is attributed to the strong intramolecular charge transfer and the backbone coplanarity of the thiophene moieties. The order of both crystallinity and FET mobility (×10^?2–×10^?4 cm² V^?1 s^?1) is TT2DPP > 4T2DPP > 2T2DPP >DTT2DP, which differ in the structure of the π‐conjugated cores and core symmetry. Well‐ordered intermolecular chain packing was confirmed by the GIXD and AFM results. In particular, the FET hole mobility of TT2DPP was further improved to 0.1 cm² V^?1 s^?1, which was attributed to the well‐interconnected structure through solution‐shearing. These experimental results suggest the potential applications of the new DPP? thiophene? DPP conjugated materials for organic electronic devices.     

The Correlation of Electrochemical Measurements and Molecular Junction Conductance Simulations in β‐Strand Peptides

Understanding the electronic properties of single peptides is not only of fundamental importance, but it is also paramount to the realization of peptide‐based molecular electronic components. Electrochemical and theoretical studies are reported on two β‐strand‐based peptides, one with its backbone constrained with a triazole‐containing tether introduced by Huisgen cycloaddition (peptide 1 ) and the other a direct linear analogue (peptide 2 ). Density functional theory (DFT) and non‐equilibrium Green’s function were used to investigate conductance in molecular junctions containing peptides 3 and 4 (analogues of 1 and 2 ). Although the peptides share a common β‐strand conformation, they display vastly different electronic transport properties due to the presence (or absence) of the side‐bridge constraint and the associated effect on backbone rigidity. These studies reveal that the electron transfer rate constants of 1 and 2 , and the conductance calculated for 3 and 4 , differ by approximately one order of magnitude, thus providing two distinctly different conductance states and what is essentially a molecular switch. A definitive correlation of electrochemical measurements and molecular junction conductance simulations is demonstrated using two different charge transfer techniques. This study furthers our understanding of the electronic properties of peptides at the molecular level, which provides an opportunity to fine‐tune their molecular orbital energies through suitable structural manipulation.     

Theoretically Rational Designs of Transport Organic Semiconductors Based on Heteroacenes

A Marcus electron transfer theory coupled with an incoherent polaron hopping and charge diffusion model in combining with first‐principle quantum chemistry calculation was applied to investigating the effects of heteroatom on the intermolecular charge transfer rate for a series of heteroacene molecules. The influences of intermolecular packing and charge reorganization energy were discussed. It was found that the sulphur and nitrogen substituted heteroacenes were intrinsically hole‐transporting materials due to the reduced hole reorganization energy and the enhanced overlap between HOMOs. For the oxygen‐substituted heteroacene, it was found that both the electronic couplings and the reorganization energies for holes and electrons were comparative, indicating the application potential of ambipolar devices. Most interestingly, for the boron‐substituted heteroacenes, theoretical calculations predicted a promising electron‐transport material, which is rare for organic materials. These findings provide insights into rationally designing organic semiconductors with specific properties.     

Phthalimide and Naphthalimide end‐Capped Diketopyrrolopyrrole for Organic Photovoltaic Applications

Two small molecules named PI‐DPP and NI‐DPP with a DPP core as the central strong acceptor unit and phthalimide/naphthalimide as the terminal weak acceptor were designed and synthesized. The effects of terminal phthalimide/naphthalimide units on the thermal behavior, optical and electrochemical properties, as well as the photovoltaic performance of these two materials were systematically studied. Cyclic voltammetry revealed that the lowest unoccupied molecular orbitals (LUMO) (~ ‐3.6 eV) of both molecules were intermediate to common electron donor (P3HT) and acceptor (PCBM). This indicated that PI‐DPP and NI‐DPP may uniquely serve as electron donor when blended with PCBM, and as electron acceptor when blended with P3HT, where sufficient driving forces between DPPs and PCBM, as well as between P3HT and DPPs should be created for exciton dissociation. Using as electron donor materials, PI‐DPP and NI‐DPP devices exhibited low power conversion efficiencies (PCEs) of 0.90% and 0.76% by blending with PCBM, respectively. And a preliminary evaluation of the potential of the NI‐DPP as electron acceptor material was carried out using P3HT as a donor material, and P3HT: NI‐DPP device showed a PCE of 0.6%, with an open circuit voltage (V _OC) of 0.7 V, a short circuit current density (J _SC) of 1.91 mA•cm^‐2, and a fill factor (FF) of 45%.     

含B-N相互作用偶氮苯强荧光材料光电性质的理论研究

本文基于增大光谱发光强度的结构修饰方法,采用理论计算方法研究了结构修饰后分子的电子性质、光谱性质以及电荷传输性质的变化.计算结果表明,-N(CH3)2取代、-N(CH3)2和-Br组合取代有助于吸收/发射光谱发光强度的提高.与母体分子相比,-N(CH3)2和-Br取代位置不同或取代数量不同可以引起最高占据分子轨道能量(EHOMO)、最低空分子轨道能量(ELUMO)和能隙(Eg=ELUMO-EHOMO)发生明显变化,从而有效调节了最大吸收波长(λabs)和最大发射波长(λem),从理论角度设计了一系列蓝光和绿光材料.重组能计算显示,除了GM-1和GM-6,其余分子可以作为有机电致发光材料(OLEDs)中的空穴传输材料,GM-1和GM-7可以作为双极性电荷传输材料.     

Computational studies of boron‐ and nitrogen‐doped single‐walled carbon nanotubes as potential sensor materials of hydrogen halide molecules HX (X = F,Cl, Br)

Potential applicability of undoped, B‐, and N‐doped carbon nanotubes (CNTs) for elaboration of the working materials of gas sensors of hydrogen halide molecules HX (X = F, Cl, Br) is analyzed in computational studies of molecular adsorption on the CNTs surfaces. Density Functional Theory (DFT)‐based geometry‐optimized calculations of the electronic structure of undoped, B‐, and N‐doped CNTs of (3,3) and (5,5) chiralities with adsorbed HX (X = F, Cl, Br) molecules are performed within molecular cluster approach. Relaxed geometries, binding energies between the adsorbates and the nanotubes, charge states of the adsorbates and the electronic wave function contours are calculated and analyzed in the context of gas sensing applications. Obtained results are supplemented by calculations of adsorption of hydrogen halides on B(N)‐doped graphene sheets which are considered as model approximation for large‐diameter CNTs. It is found that the B‐doped CNTs are perspective for elaboration of sensing materials for detection of HCl and HBr molecules. The undoped and the N‐doped CNTs are predicted to be less suitable materials for detection of hydrogen halide gases HX (X = F, Cl, Br). © 2015 Wiley Periodicals, Inc.     

Binding at molecule/gold transport interfaces. V. Comparison of different metals and molecular bridges

The geometric and electronic structural properties of symmetric and asymmetric metal cluster-molecule-cluster' complexes have been explored. The metals include Au, Ag, Pd, and Al, and both benzenedithiol and the three isometric forms of dicyanobenzene are included as bridging molecules. Calculated properties such as cluster-molecule interface geometry, electronic state, degree of metal --> molecule charge transfer, metal-molecule mixing in the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy region, the HOMO-LUMO gap, cluster --> cluster' charge transfer as a function of external field strength and direction, and the form of the potential profile across such complexes have been examined. Attempts are made to correlate charge transport with the characteristics of the cluster-complex systems. Indications of rectification in complexes that are asymmetric in the molecule, clusters, and molecule-cluster interfaces are discussed. The results obtained here are only suggestive because of the limitations of the cluster-complex model as it relates to charge transport.     

Structural,Electronic and Optical Properties of Multifunctional Iridium(III) and Platinum(II) Metallophosphors for Organic Light‐Emitting Diodes

An elaborated theoretical investigation on the optical and electronic properties of three fluorene‐based platinum(II) and iridium(III) cyclometalated complexes Pt‐a , Ir‐a and Ir‐b is reported. The geometric and electronic structures of the complexes in the ground state are studied with density functional theory and Hartree Fock approaches, while the lowest triplet excited states are optimized by singles configuration interaction (CIS) methods. At the time‐dependent density functional theory (TD‐DFT) level, molecular absorption and emission properties were calculated on the basis of optimized ground‐ and excited‐state geometries, respectively. The computational results show that the appearance of triphenylamino (TPA) moiety at the 9‐position of fluorene ring favors the hole‐creation and leads to red‐shifts of absorption and emission spectra. Moreover, Pt‐a and Ir‐b are nice hole‐transporting materials whereas Ir‐a has good charge‐transfer balance, which render them useful for the realization of efficient OLEDs (Organic Light‐Emitting Diodes).     

A quantum theory atoms in molecules investigation of Lewis base protonation

This investigation uses atomic properties derived from the quantum theory of atoms in molecules formalism to rationalize the infrared intensity of the stretching vibration that arises as a Lewis base (B) is protonated (B‐H mode). Moreover, the interacting quantum atom (IQA) partition is employed to evaluate the energetics of protonation. All calculations are performed at the CCSD/cc‐pVQZ level except by the IQA analysis, which is carried out by means of the B3LYP/cc‐pVQZ//CCSD/cc‐pVQZ treatment. First, an efficiency scale is established for Lewis bases in terms of the electronic charge transfer potential. Next, this study shows that the intensity of the B‐H stretching depends mostly on the electronic charge amount transferred to the proton. Thus, intensity data provide empirical assessment of Lewis base charge transfer efficiency. Finally, the group separation observed during correlation of proton affinities and electronic charge transfer potential is explained by the interaction energy between fragments of the protonated system.     

Comparison of the electronic structure of different perylene‐based dye‐aggregates

Aggregates of functionalized polycyclic aromatic molecules like perylene derivatives differ in important optoelectronic properties such as absorption and emission spectra or exciton diffusion lengths. Although those differences are well known, it is not fully understood if they are caused by variations in the geometrical orientation of the molecules within the aggregates, variations in the electronic structures of the dye aggregates or interplay of both. As this knowledge is of interest for the development of materials with optimized functionalities, we investigate this question by comparing the electronic structures of dimer systems of representative perylene‐based chromophores. The study comprises dimers of perylene, 3,4,9,10‐perylene tetracarboxylic acid bisimide (PBI), 3,4,9,10‐perylene tetracarboxylic acid dianhydride (PTCDA), and diindeno perylene (DIP). Potential energy curves (PECs) and characters of those electronic states are investigated which determine the optoelectronic properties. The computations use the spin‐component‐scaled approximate coupled‐cluster second‐order method (SCS‐CC2), which describes electronic states of predominately neutral excited (NE) and charge transfer (CT) character equally well. Our results show that the characters of the excited states change significantly with the intermolecular orientation and often represent significant mixtures of NE and CT characters. However, PECs and electronic structures of the investigated perylene derivatives are almost independent of the substitution patterns of the perylene core indicating that the observed differences in the optoelectronic properties mainly result from the geometrical structure of the dye aggregate. It also hints at the fact that optical properties can be computed from less‐substituted model compounds if a proper aggregate geometry is chosen. © 2012 Wiley Periodicals, Inc.     

Rational design of donor–π–acceptor n-butyl-1,8-naphthalimide-cored branched molecules as charge transport and luminescent materials for organic light-emitting diodes

Four D–π–A bipolar molecules with n-butyl-1,8-naphthalimide (BNI) fragments as acceptors, acetylenes as π-spacers, and different aromatic groups as donors have been designed to explore their optical, electronic, and charge transport properties as charge transport and luminescent materials for organic light-emitting diodes (OLEDs). The frontier molecular orbitals (FMOs) and local density of states analysis have turned out that the vertical electronic transitions of absorption and emission are characterized as intramolecular charge transfer (ICT). The calculated results show that their optical and electronic properties are affected by the different donors of the bipolar molecules. Our results suggest that D–π–A 1,8-naphthalimide derivatives with donors triphenylamine (1), 1-nitrobenzene (2), anisole (3), and 4-phenylbenzo[c][1,2,5]thiadiazole (4) fragments are expected to be promising luminescent materials. Furthermore, 2–4 are expected to be promising candidates for both electron and hole transport materials as well as potential ambipolar charge transport material, whereas BNI and 1 can serve as hole transfer materials only. We have also predicted the mobility of 4 with better performance in three different space groups. On the basis of investigated results, we proposed a rational way for the design of charge transport and/or luminescent materials simultaneously.