A Four-Step Synthesis of Substituted 5,11-Dicyano-6,12-diaryltetracenes with Enhanced Stability and High Fluorescence Emission.

A four-step synthesis of substituted 5,11-dicyano-6,12-diaryltetracenes was developed, starting from readily available para-substituted benzophenones. The key step of this straightforward route is the complex cascade reaction between tetraaryl[3]cumulenes and tetracyanoethene (TCNE) resulting in 5,5,11,11-tetracyano-5,11-dihydrotetracenes. The mechanism of this transformation was reinvestigated by means of theoretical calculations. The target tetracenes were obtained by a newly developed decyanation/aromatization reaction catalyzed by CuI or CuII complexes in solution, conditions compatible with a broad range of functional groups. A computational mechanistic study sheds light on this transformation. Structures of all tetracene derivatives were confirmed by X-ray crystallography. The presented dicyanotetracene derivatives exhibit outstanding optoelectronic properties and enhanced photostability, significantly surpassing the reference rubrene (5,6,11,12-tetraphenyltetracene).

Infrared and Raman Spectroscopy of Methylcyanodiacetylene (CH3 C5 N).

A spectroscopic study combining IR absorption and Raman scattering is presented for methylcyanodiacetylene (CH3 C5 N). Gas-phase, cryogenic matrix-isolated, and pure solid-phase substance was analyzed. Out of 16 normal vibrational modes, 14 were directly observed. The analysis of the spectra was assisted by quantum chemical calculations of vibrational frequencies, IR absorption intensities, and Raman scattering activities at density functional theory and ab initio levels. Previous assignments of gas-phase IR absorption bands were revisited and extended.

Synthesis, Chemistry, and Photochemistry of Methylcyanobutadiyne in the Context of Space Science.

An alternative preparation of methylcyanobutadiyne (MeC5N), a molecule present in the interstellar medium, was established in order to circumvent tedious steps from previous methods. The possibility of forming methylcyanoacetylene and MeC5N by gas-phase photolysis was evaluated from relevant acetylene derivatives in the context of space science. The reactivity of MeC5N toward simple nucleophiles was investigated. The exclusive formation of E adducts was observed, together with a solvent dependence for the regioselectivity of the addition.

Gas-Phase Infrared Spectroscopy of Substituted Cyanobutadiynes: Roles of the Bromine Atom and Methyl Group as Substituents.

The IR spectra of 5-bromo-2,4-pentadiynenitrile (Br-C≡C-C≡C-CN) and 2,4-hexadiynenitrile (CH3 -C≡C-C≡C-CN), a compound of interstellar interest, have been recorded within the 4000-500 cm(-1) spectral region and calculated by means of high-level ab initio and density functional calculations. Although the calculated structures of both compounds are rather similar, there are very subtle differences, mainly in the strength of the C≡C bond not directly bound to the substituent. These subtle bonding differences are reflected in small, but not negligible, differences in the electron density at the corresponding bond critical points, and, more importantly, are reflected in the IR spectra. Indeed, the IR spectrum for the bromine derivative presents two well-differentiated strong bands around 2250 cm(-1) , whereas for the methyl derivative both absorptions coalesce in a single band. These bands correspond in both cases to the coupling between C≡C and C≡N stretching displacements. A third, very weak, band also associated with C≡C and C≡N coupled stretches is observed for the bromine derivative, but not for the methyl one, owing to its extremely low intensity.

Straightforward synthesis of 5-bromopenta-2,4-diynenitrile and its reactivity towards terminal alkynes: a direct access to diene and benzofulvene scaffolds.

The high-yielding synthesis of 5-bromopenta-2,4-diynenitrile (BrC5 N) was achieved for the first time. Its reactivity with triisopropylsilylacetylene and triisopropylsilylbutadiyne in the presence of copper and palladium as co-catalysts and diisopropylamine was evaluated. It revealed an unprecedented cascade reaction leading to a diene in one case and to a benzofulvene in the other case, with a unique structure. Both of them were characterized by X-ray crystallography, among other techniques. The mechanism of the reaction leading to the diene was investigated experimentally. Theoretical calculations at the DFT level suggest that the mechanism leading to the benzofulvene relies on a hexa-dehydro Diels-Alder (HDDA)-type of mechanism. This work constitutes an example of an unanticipated reactivity leading to an important increase of chemical complexity.

High-yield formation of substituted tetracyanobutadienes from reaction of ynamides with tetracyanoethylene.

A high-yielding sequence of [2+2] cycloaddition-retroelectrocyclization of ynamides with tetracyanoethylene (TCNE) is described. The reaction provided tetracyanobutadiene (TCBD) species, which were characterized by various techniques. DFT and TD-DFT calculations were also performed to complement experimental findings.