Hetero Diels–Alder Reactions with a Dicationic Urea Azine Derived Azo Dienophile and Their Use for the Synthesis of an Electron-Rich Pentacene

Herein, the first hetero Diels–Alder (DA) reactions with a stable, dicationic urea azine derived azo dienophile, synthesized by two-electron oxidation of a neutral urea azine are reported. Several charged DA products were synthesized in good yield and fully characterized. The DA adduct of anthracene is in thermal equilibrium with the reactants at room temperature, and the reaction enthalpy and entropy were determined from the temperature-dependent equilibrium constant. Furthermore, base addition to solutions of the pentacene DA product led to deprotonation, cleavage of the N−N bond, and formation of an electron-rich 6,13-bisguanidinyl-substituted pentacene. The redox and optical properties of this new pentacene derivative were studied. Furthermore, the dication resulting from its two-electron oxidation was synthesized and fully characterized. The results disclose a new elegant route to electron-rich pentacene derivatives.     

From Byproducts to Efficient Fluorophores: A Route to the Synthesis of Fluorubines

The reaction of bis(imidoyl) chlorides of oxalic acid with monoalkyl hydrazines leads to substituted Δ²‐1,2‐diazetines, which are versatile building blocks for ring‐transformation reactions. One remarkable product originating from side reactions featured by a strong orange/red fluorescence was confirmed as a novel fluorubine derivative. In continuing our studies to substituted oligoazaacenes, we developed several synthetic entries to build up novel fluorubine derivatives, in which particularly aminobridged bis(quinoxaline)s are the key products for cationic hexaazapentacenes. We would like to discuss the possible formation pathways of these fluorubine derivatives, which exhibit interesting photophysical and chemical properties. The structures of all new derivatives were confirmed by common analytical methods (NMR spectroscopy, CV, UV/Vis, mass spectrometry, elemental analysis, and X‐ray structural analysis) and will be discussed on selected examples in more detail.     

Synthesis of 1,2,3,4,8,9,10,11‐Octasubstituted Pentacenequinone Derivatives and their Conversion into Substituted Pentacenes

A series of 1,2,3,4,8,9,10,11‐octasubstituted pentacenequinone derivatives were prepared by the oxidation of 1,2,3,4,8,9,10,11‐octasubstituted pentacenes, which were synthesized by the double homologation method. Oxidation of the pentacenes was carried out with H₅IO₆ or air and DDQ. These octasubstituted pentacenequinones were converted into 1,2,3,4,6,8,9,10,11,13‐decasubstituted or 2,3,6,9,10,13‐hexasubstituted pentacene derivatives by the introduction of aryl or alkynyl groups at the carbonyl carbons. The photophysical properties of these new pentacenes have been measured in solution, and the substituent effects are discussed.     

孤立轨道法评估不同并五苯分子堆积的电荷转移积分

运用量子化学密度泛函理论B3LYP方法, 在6-31G(d,p)水平上采用孤立轨道法的双分子非自洽与自洽法评估了基于π共轭有机半导体材料不同堆积的并五苯二聚体的电荷转移积分, 在此基础上考虑电场作用对以上堆积形式下电荷转移积分的影响. 结果表明, 孤立轨道的双分子自洽方法得到的有效转移积分与非自洽法得到的直接耦合量在数值上非常接近并与实验值比较吻合, 且自洽法还可以方便地考察极化对分子位点能的影响. 此外, 运用该方法在电场作用下评估了不同堆积形式下的并五苯二聚体的电荷转移积分, 结果表明电场对电荷转移积分几乎没有影响.     

Cyanation: providing a three-in-one advantage for the design of n-type organic field-effect transistors

The theoretical work presented here demonstrates that, when substitution takes place at appropriate positions, cyanation could be a useful tool for reducing the internal reorganization energy of molecules. A molecular-orbital-based explanation is given for this fundamentally important phenomenon. Some of the cyanated pentacene derivatives (nCN-PENT-n) not only have internal reorganization energies for electron transfer (lambda(-)) smaller than that of pentacene, but the lambda(-) values are even of the same magnitude as the internal reorganization energy for hole transfer (lambda(+)) of pentacene, a small value that few organic compounds have surpassed. In addition, cyanation raises the electron affinity of the parent compound and may afford good electronic couplings between neighboring molecules, because of its ability in promoting pi-stacking. For the design of high performance n-Type Organic field-effect transistors, high electron affinities, large intermolecular electronic couplings, and small reorganization energies are necessary. Cyanation may help in all three aspects. Two cyanated trialkylsilylethynyl pentacene derivatives with known pi-stacking structures are predicted to provide reasonably small internal reorganization energies, large electronic couplings, and high electron affinities. They have the potential to outperform N-fluoroalkylated dicyanoperylene-3,4:9,10-bis(dicarboximides) (PDI-FCN(2)) in terms of electron mobility.     

Crystal-plane-dependent photoluminescence of pentacene 1D wire and 2D disk crystals

Down to the wire: Pentacene exhibits crystal-plane-dependent photoluminescence (PL) activity, as demonstrated in highly crystalline 1D?wires and 2D?disks, which were selectively synthesized using the vaporization-condensation-recrystallization (VCR) process. Although pentacene 1D?wires and 2D?disks have identical triclinic crystal structures, PL?activity is observed only from pentacene 1D?wires owing to the presence of "PL-active" (010) planes.     

Exploring Crystal Structure in Ethyne‐Substituted Pentacenes,and Their Elaboration into Crystalline Dehydro[18]annulenes

Approaches to control the self‐assembly of aromatic structures to enhance intermolecular electronic coupling are the key to the development of new electronic and photonic materials. Acenes in particular have proven simple to functionalize to induce strong π‐stacking interactions, although finer control of intermolecular π‐overlap has proven more difficult to accomplish. In this report, we describe how very weak hydrogen bonding interactions can exert profound impact on solid‐state order in solubilized pentacenes, inducing self‐assembly in either head‐to‐tail motifs with strong 2‐D π‐stacking, or head‐to‐head orientations with much weaker, 1‐D π‐stacking arrangements. In order to achieve 3‐D π‐stacking useful for photovoltaic applications, we elaborated a series of diethynyl pentacenes to their trimeric dehydro[18]annulene forms. These large, strongly interacting structures did indeed behave as acceptors in polymer photovoltaic devices.     

Pentacene‐Fused Diporphyrins

In this work, we report the synthesis, spectroscopic characterization, and theoretical analysis of a linearly conjugated pentacene‐fused porphyrin dimer and cross‐conjugated quinone‐fused dinaphtho[2,3]porphyrins. These multichromophoric systems display non‐typical UV‐visible absorptions of either porphyrins or pentacenes/quinones. UV‐visible, emission and magnetic circular dichroism (MCD) spectroscopy suggest strong electronic interactions among the multichromophores in the system. DFT calculations revealed the delocalization of the HOMOs and LUMOs spanning the entire dimer and linker assembly. The pentacene‐fused porphyrin dimer is significantly more stable than both the corresponding pentacene and the heptacene derivatives. The availability of these huge π‐extended and electronically highly interactive multichromophoric systems promises unprecedented electronic and photophysical properties.