Synthesis, photophysics and excited state structure of 1,8-di(p-tolyl)-1,3,5,7-octatetrayne

Optical gap and fundamental gap of oligoynes and carbyne

The optoelectronic properties of various carbon allotropes and nanomaterials have been well established, while the purely sp-hybridized carbyne remains synthetically inaccessible. Its properties have therefore frequently been extrapolated from those of defined oligomers. Most analyses have, however, focused on the main optical transitions in UV-Vis spectroscopy, neglecting the frequently observed weaker optical bands at significantly lower energies. Here, we report a systematic photophysical analysis as well as computations on two homologous series of oligoynes that allow us to elucidate the nature of these weaker transitions and the intrinsic photophysical properties of oligoynes. Based on these results, we reassess the estimates for both the optical and fundamental gap of carbyne to below 1.6 eV, significantly lower than previously suggested by experimental studies of oligoynes.

Carbyne, a linear sp-hybridized carbon allotrope, is synthetically inaccessible and its properties are extrapolated from those of defined oligomers. Here the authors analyze weak optical bands in two series of oligoynes and reassess the optical and fundamental gap of carbyne to lower values than previously suggested.

1-Iodobuta-1,3-diynes in Copper-Catalyzed Azide-Alkyne Cycloaddition: A One-Step Route to 4-Ethynyl-5-iodo-1,2,3-triazoles

Cu-catalyzed 1,3-dipolar cycloaddition of iododiacetylenes with organic azides using iodotris(triphenylphosphine)copper(I) as a catalyst was found to be an efficient one-step synthetic route to 5-iodo-4-ethynyltriazoles. The reaction is tolerant to various functional groups in both butadiyne and azide moieties. The synthetic application of 5-iodo-4-ethynyl triazoles obtained was also evaluated: the Sonogashira coupling with alkynes resulted in unsymmetrically substituted triazole-fused enediyne systems, while the Suzuki reaction yielded the corresponding 5-aryl-4-ethynyl triazoles.

Spectral dependence of nonlinear optical properties of symmetrical octatetraynes with p-substituted phenyl end-groups

Organic compounds containing conjugated carbon chains have been extensively investigated due to their interesting properties including nonlinear optical response.

Photophysics of threaded sp-carbon chains: the polyyne is a sink for singlet and triplet excitation

We have used single-crystal X-ray diffraction and time-resolved UV-NIR-IR absorption spectroscopy to gain insights into the structures and excited-state dynamics of a rotaxane consisting of a hexayne chain threaded through a phenanthroline macrocycle and a family of related compounds, including the rhenium(I) chlorocarbonyl complex of this rotaxane. The hexayne unit in the rhenium-rotaxane is severely nonlinear; it is bent into an arc with an angle of 155.6(1)° between the terminal C1 and C12 atoms and the centroid of the central C-C bond, with the most acute distortion at the point where the polyyne chain pushes against the Re(CO)3Cl unit. There are strong through-space excited-state interactions between the components of the rotaxanes. In the metal-free rotaxane, there is rapid singlet excitation energy transfer (EET) from the macrocycle to the hexayne (τ = 3.0 ps), whereas in the rhenium-rotaxane there is triplet EET, from the macrocycle complex (3)MLCT state to the hexayne (τ = 1.5 ns). This study revealed detailed information on the short-lived higher excited state of the hexayne (lifetime ∼1 ps) and on structural reorganization and cooling of hot polyyne chains, following internal conversion (over ∼5 ps). Comparison of the observed IR bands of the excited states of the hexayne with results from time-dependent density functional calculations (TD DFT) shows that these excited states have high cumulenic character (low bond length alternation) around the central region of the chain. These findings shed light on the complex interactions between the components of this supramolecular rotaxane and are important for the development of materials for the emerging molecular and nanoscale electronics.