Nonalternant Aromatic Hydrocarbons Research Articles

INCLUSION OF AZULENE STRUCTURAL UNITS IN THE BASIS OF CONJUGATED POLYMERS: IMPROVEMENT OF PROTON SENSITIVITY AND FLUORESCENCE

The growing interest in aromatic polymer compounds with an extended π-electron coupling system is explained by their importance as functional materials for organic optoelectronics. At present, much attention is paid to arylated, as well as substituted by electron acceptor and/or electron donor groups, aromatic and heteroaromatic compounds. One of the advantages of such conjugated aromatic systems is that they can fine-tune the electronic structure of materials in order to optimize their performance and morphology. In this regard, the structural isomer of naphthalene - azulene is of considerable interest. The nonalternant aromatic hydrocarbon azulene has unique electronic and spectral properties, including a polarized structure with a dipole moment of the order of 1,08 D and abnormal Anti-Kasha fluorescence S2→S0. The article discusses the synthesis of two fluorene-azulene π-conjugated copolymers using the modern methodology of organic synthesis as the Suzuki − Miyaura -cross−coupling reaction. It was shown that the interaction of 1,3-dibromazulene, as well as 2,7-Bis(3-bromoazulen-1-yl)-9,9-dioctyl-fluorene with 2,2'-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(1,3,2-dioxaborinane) under Suzuki − Miyaura cross-coupling conditions, azulene conjugate copolymers were synthesized: poly[2,7-(9,9-dioctylfluorenyl)-alt-(1ꞌ,3ꞌ - azulenyl)] and poly[1,3-bis(9ꞌ,9ꞌ-dioctylfluoren-2ꞌ-yl)azulenyl]-alt-[1ꞌꞌ,3ꞌꞌ - azulenyl]. It is revealed that neutral solutions of the obtained copolymers are nonfluorescent, but they become luminescent upon addition of trifluoroacetic acid. The «launching» of fluorescence occurs as a result of the formation of a 6 π-electron azulenyl cation, which rearranges the general electronic character of polymers, in particular, HOMO-LUMO levels and band gap. The obtained results demonstrate that the introduction of azulene units into a conjugated polymer framework has great potential for application as new protic functional materials.

Molecular Topology and the Surface Chemical Bond: Alternant Versus Nonalternant Aromatic Systems as Functional Structural Elements

The nonalternant aromatic hydrocarbon azulene bonds much more strongly to copper than its alternant isomer naphthalene, illustrating the critical role of molecular topology in controlling metal-organic interfaces in electronic devices.

ChemInform Abstract: Azulene‐Based Organic Functional Molecules for Optoelectronics

AbstractReview: 82 refs.

Azulene-based organic functional molecules for optoelectronics

Abstract Design and synthesis of new organic functional materials with improved performance or novel properties are of great importance in the field of optoelectronics. Azulene, as a non-alternant aromatic hydrocarbon, has attracted rising attention in the last few years. Different from most common aromatic hydrocarbons, azulene has unique characteristics, including large dipole moment, small gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). However, the design and synthesis of azulene-based functional materials are still facing several challenges. This review focuses on the recent development of organic functional materials employing azulene unit. The synthesis of various functionalized azulene derivatives is summarized and their applications in optoelectronics are discussed, with particular attention to the fields including nonlinear optics (NLO), organic field-effect transistors (OFETs), solar cells, and molecular devices.

Unexpected electrochemical reduction of fluoranthene in the solvents DME and HMPA: new light onto the mechanism of hydrogenation to produce tetrahydrofluoranthene

The non-alternant aromatic hydrocarbon fluoranthene (Ar0) has been reduced, either chemically with Na or Li or by electrolysis, to the radical anion Ar˙– in the three solvents THF (tetrahydrofuran), DME (dimethoxyethane) and HMPA (hexamethylphosphoric triamide). The UV–VIS absorption spectrum of the orange–brown Ar˙– is quite similar in the three solvents and in all instances addition of H+–H2O has resulted in quantitative electron-back-donation along with H2 evolution and recovery of unchanged fluoranthene Ar0. Thus the usual Birch-type reduction to a dihydro derivative is totally inefficient in the cases under investigation. The two-electron reduction has also been achieved in these three solvents. The greenish-yellow dianion Ar2– produced in THF exhibits characteristic UV–VIS absorption patterns, disproportionates with Ar0 and reacts with H+–H2O only to evolve H2.With DME or HMPA a blood-red species is produced whose absorption spectrum is virtually the same and quite different from that observed in THF. In both solvents addition of H+–H2O leads to tetrahydrofluoranthene as a main reaction product but disproportionation is not observed at all in HMPA and this is not compatible with a regular dianion Ar2–.Reaction with D+–D2O instead of H+–H2O has shown that hydrogenation involves radical abstraction of H atoms from the solvent in both cases; this sheds new light onto the reaction mechanism. Furthermore, several other experiments indicate that the dianionic blood-red species is most likely a complex written as [Ar˙–⋯˙– Solvent], in which the Ar˙– moiety is bound to a solvated electron localized on a solvent molecule.

Mechanisms of electrochemical hydrogenation of fluoranthene in HMPA with ethanol and aqueous HCL as proton donors

The electrochemical hydrogenation of the non-alternant aromatic hydrocarbon fluoranthene has been investigated in LiClO4-hexamethylphosphoric triamide; it has been found that hydrogenation cannot be achieved satisfactorily, not even to the dihydro derivative, when ethanol is used as the proton donor, whether present during or added after electrolysis. On the other hand, reaction of a stock of fluoranthene dianion with aqueous hydrochloric acid proves to be a clean, easy way to prepare 1,2,3,10b-tetrahydrofluoranthene, a product which requires donation of four electrons to fluoranthene. A mechanism is discussed to account for such a transfer of electrons.

Electron Spin Resonance of the Radical Ions of an Isomeric Alternant and Nonalternant Aromatic Hydrocarbon

Electron spin resonance (ESR) spectra have been obtained for the negative ions of the nonalternant aromatic hydrocarbon Δ9,9′-bifluorene, and for its even alternant structural isomer, dibenzo(a,c)triphenylene. Coupling constants have been determined and compared with those obtained for the positive ions and with spin densities calculated from Hückel molecular orbital (HMO) theory.

Absence d’effet hypsochrome dans le spectre ultra-violet de dérivés du fluoranthène

Hypsochromic shifts produced by substitution in non-alternant aromatic hydrocarbons can be interpreted in terms of simple molecular orbital theory. On that ground, the NH 3 + radical is best suited to bring about hypsochromic shifts. However, no such effect has been observed in fluoranthene, which therefore behaves like an alternant hydrocarbon. This could be ascribed to the reduced conjugation between the benzene and the naphthalene nuclei in this molecule.