Rhodium‐Catalyzed Cross‐Cyclotrimerization and Dimerization of Allenes with Alkynes

It has been established that a cationic rhodium(I)/binap complex catalyzes the cross‐cyclotrimerization of two molecules of a monosubstituted allene with one molecule of a functionalized alkyne to give 3,6‐dialkylidenecyclohex‐1‐enes. In contrast, the reactions involving di‐ or trisubstituted allenes and/or unfunctionalized alkynes afforded cross‐dimerization products, substituted dendralenes, through β‐hydrogen elimination from the corresponding rhodacycles.     

Unexpected Michael Additions on the Way to 2.3,8.9‐Dibenzanthanthrenes with Interesting Structural Properties

The synthesis and properties of a new polycyclic aromatic hydrocarbon containing eight annulated rings and based on the anthanthrene core is described. An unexpected, nucleophile‐dependent Michael addition to a dibenzanthanthrene‐1,7‐dione is found, giving a product with three triisopropylsilylacetylene units and a remarkable solid‐state structure (as determined by X‐ray crystallography).     

FT Raman and DFT Study on a Series of All‐anti Oligothienoacenes End‐Capped with Triisopropylsilyl Groups

Herein, we study the π‐conjugational properties of a homologous series of all‐anti oligothienoacenes containing four to eight fused thiophene rings by means of FT Raman spectroscopy and DFT calculations. The theoretical analysis of the spectroscopic data provides evidence that selective enhancement of a very limited number of Raman scatterings is related to the occurrence in these oligothienoacenes of strong vibronic coupling between collective ν(C?C) stretching modes in the 1600–1300 cm^?1 region and the HOMO/LUMO frontier orbitals (HOMO=highest occupied molecular orbital; LUMO=lowest unoccupied molecular orbital). The correlation of the Raman spectroscopic data and theoretical results for these all‐anti oligothienoacenes with those previously collected for a number of all‐syn oligothienohelicenes gives further support to the expectation that cross‐conjugation is dominant in heterohelicenes. Fully planar all‐anti oligothienoacenes display linear π conjugation which seemingly does not reach saturation with increasing number of annulated thiophene rings in the oligomeric chain at least up to the octamer.     

Higher Acenes by On‐Surface Dehydrogenation: From Heptacene to Undecacene

A unified approach to the synthesis of the series of higher acenes up to previously unreported undecacene has been developed through the on‐surface dehydrogenation of partially saturated precursors. These molecules could be converted into the parent acenes by both atomic manipulation with the tip of a scanning tunneling and atomic force microscope (STM/AFM) as well as by on‐surface annealing. The structure of the generated acenes has been visualized by high‐resolution non‐contact AFM imaging and the evolution of the transport gap with the increase of the number of fused benzene rings has been determined on the basis of scanning tunneling spectroscopy (STS) measurements.     

Wide Band Gap Non‐Fullerene Small Molecular Acceptors Containing Spirobifluorene and Benzotriazole with Three Different End‐Capped Groups for P3HT‐Based Organic Solar Cells

Spirofluorene (SF) and benzo[d][1,2,3]triazole (BTA) have been considered as promising building blocks to construct n‐type photovoltaic materials. Herein, three new small molecule acceptors (SMAs) named BTA21 , BTA23 and BTA27 with the structure of A₂ = A₁‐D‐A₁ = A₂ have been designed, in which SF and BTA were used as a central unit of D and bridged acceptor unit of A₁, respectively. In addition, 3‐ethylrhodanine, 2‐(3‐ethyl‐4‐ oxothiazolidin‐2‐ylidene)malononitrile and malononitrile were chosen as terminal acceptor units to modulate the properties of the final SMAs. Three SMAs show wide optical band gaps (E_g) of 2.19, 2.15 and 2.21 eV, respectively, with gradually down‐shift of the lowest unoccupied molecular orbital (LUMO) levels in the order of BTA21 , BTA23 and BTA27 depending on the electron‐withdrawing capability of terminal acceptor units. BTA21 shows great advantages with respect to donor poly(3‐hexylthiophene) (P3HT) over BTA23 and BTA27 , such as well energy‐level matching, complementary absorption and proper morphology. Concequently, P3HT: BTA21 shows the best power conversion efficiency (PCE) value of 3.28% with an open‐circuit voltage (V_OC) of 1.02 V, a short‐circuit current (J_SC) of 5.45 mA·cm^–2 and a fill factor (FF) of 0.59. These results indicate that the terminal acceptor group end‐capped in SMAs plays a significant role in controlling their optical, electronic, and photovoltaic properties.     

Palladium(II)‐Catalyzed Tandem Synthesis of Acenes Using Carboxylic Acids as Traceless Directing Groups

A straightforward synthetic strategy for generating useful anthracene derivatives was developed involving palladium(II)‐catalyzed tandem transformation with carboxylic acids as traceless directing groups. Carboxyl‐directed C‐H alkenylation, carboxyl‐directed secondary C‐H activation and rollover, intramolecular C?C bond formation, and decarboxylative aromatization are proposed as the key steps in the tandem reaction pathway. This novel synthetic route utilizes a broad range of substrates and provides a convenient synthetic tool that allows access to acenes.     

Z‐Shaped Pentaleno‐Acene Dimers with High Stability and Small Band Gap

Acene‐based materials have promising applications for organic electronics but the major constrain comes from their poor stability. Herein a new strategy to stabilize reactive acenes, by fusion of an anti‐aromatic pentalene unit onto the zigzag edges of two acene units to form a Z‐shaped acene dimer, is introduced. The Z‐shaped acene dimers are extremely stable and show a small energy gap resulting from intramolecular donor–acceptor interactions. X‐ray crystallographic analysis revealed their unique geometry and one‐dimensional slip‐stack columnar structure. Besides optical and electrochemical characterizations, solution‐processed field‐effect transistors were also fabricated.     

Tetraaryl‐Substituted Benzo[1,2‐b:4,5‐b′]dipyrroles: Synthesis,Properties, and Applications to Hole‐Injection Materials in OLED Devices

Yes, HIMs can! A series of 2,3,6,7‐tetraarylbenzo[1,2‐b:4,5‐b′]dipyrroles (BDPs) were synthesized using zinc‐mediated double cyclization. Organic light‐emitting diodes consisting of BDP:PPB as a hole‐injection layer could be driven at a lower voltage than a PEDOT:PSS‐based device. Correlation of the IP values with the driving voltage shed some light on the mechanism of hole‐injection processes.

     

π‐Extended Indenofluorenes

A series of π‐extended aromatic indenofluorene (IF) analogues with naphthalene and anthracene cores have been synthesized through acid‐catalyzed intramolecular cyclization. The regioselectivity of the reaction is controlled by a combination of steric and electronic factors and in some cases several possible regioisomers have resulted from the same precursor. The effects of ring connectivity on the optoelectronic properties were investigated by DFT calculations, absorption/emission spectroscopy, cyclic voltammetry, and spectroelectrochemical studies. All regioisomers exhibited a redshift of their absorption/emission bands relative to the parent IF analogues, but the magnitude of this shift and other optoelectronic properties (luminescence quantum yield, etc.) depends on the ring connectivity in a less obvious manner.     

Syntheses,Phase Behavior,Supramolecular Chirality,and Field‐Effect Carrier Mobility of Asymmetrically End‐Capped Mesogenic Oligothiophenes

Supramolecular chirality and liquid crystalline OFET : Achiral end‐capped oligothiophenes can be tuned to exhibit supramolecular chirality with unique striped textures showing distinct circular dichroism signals as well as a highly ordered SmE phase that leads to high hole carrier mobility.

     

6,13‐Diethynyl‐5,7,12,14‐tetraazapentacene

A new relative of pentacene : The dialkynylated tetraazapentacene (see figure) was prepared by a two‐step synthesis from the corresponding quinone derivative. The heteroacene is an air‐stable, dark‐blue, crystalline material and is of great interest as a potential organic n‐electron‐transport material.

     

Nickel‐Catalyzed Dimerization and Alkylarylation of 1,3‐Dienes with Alkyl Fluorides and Aryl Grignard Reagents

In the presence of a nickel catalyst, 1,3‐butadiene undergoes selective dimerization and alkylarylation with alkyl fluorides and aryl Grignard reagents to give 1,6‐octadienes with alkyl and aryl groups at the 3‐ and 8‐positions, respectively, by the consecutive formation of three carbon–carbon bonds. The formation of an anionic nickel complex plays an important role in forming C?C bonds with alkyl fluorides.     

Efficient Electroluminescence from Excimers of 1,3,6,8‐Tetrakis(3,5‐dimethylphenyl)pyrene

Excimers are generally considered as detrimental to OLEDs. For pyrene‐based chromophores, however, this is not always true. In this contribution, two new methylated tetraphenylpyrenes, 1,3,6,8‐tetra‐o‐tolylpyrene (TTPy) and 1,3,6,8‐tetrakis(3,5‐dimethylphenyl)pyrene (TDMPPy), were synthesized through Suzuki coupling reactions. TDMPPy absorbs and emits light at longer wavelengths than TTPy due to its more planar conformation and thus better conjugation. TDMPPy is prone to excimer formation, thus leading to a strong bathochromic shift (84 nm) in the photoluminescence spectrum of its film. TDMPPy exhibits efficient electroluminescence originating from pyrene excimers, affording a maximum luminance of 26 670 cd m^?2 and a current efficiency as high as 10.8 cd A^?1 in a non‐doped OLED (ITO/PEDOT:PSS (50 nm)/NPB (30 nm)/TDMPPy (30 nm)/TPBI (40 nm)/Ca:Ag).     

CO2‐ and O2‐Sensitive Fluorophenyl End‐Capped Poly(ethylene glycol)

Pentafluorophenyl end‐capped poly(ethylene glycol) (PF‐PEG‐PF) aqueous solution shows a lower critical solution temperature (LCST), which is sensitive to the type of gases dissolved in the solution. LCST increases from 24.5 to 26 °C when dissolved carbon dioxide is replaced by oxygen. The transparent‐to‐turbid transition is reversibly observed when the dissolved carbon dioxide in the PF‐PEG‐PF aqueous solution is exchanged with oxygen, and vice versa, at 24.5 °C. ¹⁹F NMR and ¹H NMR spectra of the PF‐PEG‐PF in D₂O suggest that 1) dehydration of PEG is the main reason of developing LCST of the PF‐PEG‐PF aqueous solution, 2) minute differences in the intermolecular interactions, as demonstrated by changes in the chemical shift of the PF‐PEG‐PF peaks, induce such a difference in LCST. This paper provides a new insight in designing a stimuli‐responsive polymer in that fine tuning of a phase transition can be controlled by the type of dissolved gas.

     

Bottom‐up Construction of π‐Extended Arenes by a Palladium‐Catalyzed Annulative Dimerization of o‐Iodobiaryl Compounds

A straightforward method was developed for construction of aromatic compounds with a triphenylene core. The method involves Pd‐catalyzed annulative dimerization of o‐iodobiaryl compounds by double C?I and C?H bond cleavage steps. Simple reaction conditions are needed, requiring neither a ligand nor an oxidant, and the reaction tolerates a wide range of coupling partners without compromising efficiency or scalability. Significantly, the tetrachloro‐substituted synthon, 1,6,11‐trichloro‐4‐(4‐chlorophenyl)triphenylene, can be generated and used to prepare a series of fully fused, small graphene nanoribbons by a late‐stage arylation with arylboronic acids and a subsequent Scholl reaction. The synthetic strategy enables bottom‐up access to extended π‐systems in a controlled manner.     

Synthesis of Three‐Dimensional Butterfly Slit‐Cyclobisazaanthracenes and Hydrazinobisanthenes through One‐Step Cyclodimerization and Their Properties

New three‐dimensional (3D) π‐conjugated molecules, butterfly‐shaped slit‐cyclobisazaanthracenes, were synthesized in high yields by Ni‐mediated one‐step cyclodimerization of dibromoazaanthracenes with a dimethylacridine, phenothiazine, or acridone skeleton. The 3D slit butterfly shape was formed by folded azaanthracene skeletons. Closure of the slit via N?N bond formation afforded hydrazinobisanthenes with an embedded hydrazine structure in a bisanthene skeleton, which exhibited a 3D butterfly or a 2D plane structure depending on the type of heterocycle used. Extensive study of the stereoselective chemical reactivity of the butterfly shape, X‐ray analysis, DFT calculations, electrochemical/chemical oxidations, and photophysical measurements revealed that the properties of these materials included stereoselective oxidation, a rigid or flexible butterfly shape, dynamic conformational behavior, unique crystal‐packing structures, excellent electron donation with low oxidation potential, a radical cation, a long absorption wavelength, and fluorescence property.     

Site‐Directed Dimerization of Bowl‐Shaped Radical Anions to Form a σ‐Bonded Dibenzocorannulene Dimer

Designed site‐directed dimerization of the monoanion radicals of a π‐bowl in the solid state is reported. Dibenzo[a,g]corannulene (C₂₈H₁₄) was selected based on the asymmetry of the charge/spin localization in the C₂₈H₁₄^.? anion. Controlled one‐electron reduction of C₂₈H₁₄ with Cs metal in diglyme resulted in crystallization of a new dimer, [{Cs⁺(diglyme)}₂(C₂₈H₁₄?C₂₈H₁₄)^2?] ( 1 ), as revealed by single crystal X‐ray diffraction study performed in a broad range of temperatures. The C?C bond length between two C₂₈H₁₄^.? bowls (1.560(8) Å) measured at ?143 °C does not significantly change upon heating of the crystal to +67 °C. The single σ‐bond character of the C?C linker is confirmed by calculations. The trans‐disposition of two bowls in 1 is observed with the torsion angles around the central C?C bond of 172.3(5)° and 173.5(5)°. A systematic theoretical evaluation of dimerization pathways of C₂₈H₁₄^.? radicals confirmed that the trans‐isomer found in 1 is energetically favored.