Fluorination-Induced Evolution of Columnar Packing in Fluorous Triphenylenes and Benzotriphenylenes.

Invited for this month's cover are the groups of Steven Strauss/Olga Boltalina at Colorado State University, and Yu-Sheng Chen at the NSF's ChemMatCARS. The cover picture shows the evolution of fluorous triphenylene crystal packing motifs against the backdrop of the Very Large Array near Magdalena in New Mexico, where scientists study the evolution of the universe. The stepwise structural evolution in columnar packing observed was possible because of the development of a one-step selective synthesis for triphenylene(C4 F8 )n derivatives (n = 1-3). These compounds are expected to find application in liquid crystal displays and organic electronics. Read the full text of the article at 10.1002/cplu.201800451.

Fluorination-Induced Evolution of Columnar Packing in Fluorous Triphenylenes and Benzotriphenylenes.

Use of D3h -symmetrical triphenylene (TRPH) as a substrate for high-temperature radical reactions with C4 F8 I2 under varying conditions resulted in the introduction of four types of fluorinated substituents: ω-C4 F8 H, c-C4 F8 , c-C4 F4 , and c-C4 HF3 . In contrast to the previous work on direct (poly)substitutions with RF groups in polycyclic aromatic hydrocarbons (PAHs), in this work regiospecificity, selectivity, and high yield were achieved for TRPH(C4 F8 ) and TRPH(C4 F8 )3 . New single-crystal structural data for seven compounds combined with literature crystallographic data allowed for the first detailed and precise analysis of the effects of fluorous substituent types, their number, and their position(s) on the TRPH core on the solid-state packing, and more specifically, the degree of π-π overlap between neighboring molecules, which is linked to charge transport properties. Comparison of isostructural partially fluorinated benzotriphenylenes, 2,3-TRPH(C4 F4 ) and 2,3-TRPH(C4 HF3 ), revealed an unexpectedly large (30 %) drop of π-π overlap, when only one fluorine atom was replaced with the hydrogen atom in a C4 F4 moiety. Theoretical and potentially practical implications of this work may include further testing and elaboration of computational methods describing solid-state interactions and predictions of transport properties of organic semiconductors, and further advances in the molecular design of high-performing TRPH-based organic materials and supramolecular architectures for organic optoelectronics.

Copper Causes Regiospecific Formation of C4 F8 -Containing Six-Membered Rings and their Defluorination/Aromatization to C4 F4 -Containing Rings in Triphenylene/1,4-C4 F8 I2 Reactions.

The presence of Cu in reactions of triphenylene (TRPH) and 1,4-C4 F8 I2 at 360 °C led to regiospecific substitution of TRPH ortho C(ß) atoms to form C4 F8 -containing rings, completely suppressing substitution on C(α) atoms. In addition, Cu caused selective reductive-defluorination/aromatization (RD/A) to form C4 F4 -containing aromatic rings. Without Cu, the reactions of TRPH and 1,4-C4 F8 I2 were not regiospecific and no RD/A was observed. These results, supported by DFT calculations, are the first examples of Cu-promoted 1) regiospecific perfluoroannulation, 2) preparative C-F activation, and 3) RD/A. HPLC-purified products were characterized by X-ray diffraction, low-temperature PES, and (1) H/(19) F NMR.

Incremental Tuning Up of Fluorous Phenazine Acceptors.

In a simple, one-step direct trifluoromethylation of phenazine with CF3 I we prepared and characterized nine (poly)trifluoromethyl derivatives with up to six CF3 groups. The electrochemical reduction potentials and gas-phase electron affinities show a direct, strict linear relation to the number of CF3 groups, with phenazine(CF3)6 reaching a record-high electron affinity of 3.24 eV among perfluoroalkylated polyaromatics.