Tuning Redox Properties and Self-Assembly of Thienoacene-Extended Tetrathiafulvalenes

Turning on and off associations between molecules by a reversible change in their redox states is a convenient way of controlling self-assembly and hence for advancing supramolecular chemistry. Here we present systematic studies on a selection of extended tetrathiafulvalenes with thienoacene spacers. By cyclic and differential pulse voltammetry and in situ EPR/UV-Vis-NIR spectroelectrochemistry, in combination with computations, we have elucidated how the number and orientations of thiophene rings in the spacer between the two dithiafulvene rings influence both the donor strength and association properties. The radical cations and their associates were found to cover a remarkable large region of the UV-Vis-NIR spectrum, but the appearance of the absorption spectrum of the radical cations as well as of the unassociated dications also depended strongly on the exact molecular structure.

Extended Triangulenium Ions: Syntheses and Characterization of Benzo-Bridged Dioxa- and Diazatriangulenium Dyes

The very limited class of fluorophores, with a long fluorescence lifetime (>10 ns) and fluorescence beyond 550 nm, has been expanded with two benzo-fused triangulenium derivatives and two cationic [5]-helicene salts. The syntheses of the benzo-bridged dioxa- and diazatriangulenium derivatives (BDOTA⁺ and BDATA⁺, respectively) required two different synthetic approaches, which reflect the structural and physiochemical impact on the reactivity of [5]-helicenium precursors. Spectroscopic investigations show that the introduction of the benzo bridge into the triangulenium chromophore significantly redshifts the absorption and emission while maintaining fluorescence lifetimes above 10 ns. The combination of a high quantum yield, long fluorescence lifetime, and emission above 600 nm is possible only if the structural aspects of the triangulenium framework are perfectly harmonized to secure a low rate of nonradiative deactivation. The new benzo bridge may be a general motif to obtain red-shifted derivatives of other dye classes.

The role of intramolecular charge transfer and symmetry breaking in the photophysics of pyrrolo[3,2-b]pyrrole-dione

This paper reveals structurally unique π-expanded pyrrolo[3,2-b]pyrrole and its non-typical photophysical behaviour.

Highly planar diarylamine-fused porphyrins and their remarkably stable radical cations

Oxidative fusion of a meso-phenoxazino Ni(ii) porphyrin at high temperature gave a doubly phenoxazine-fused porphyrin as a highly planar diarylamine-fused porphyrin. One-electron oxidation of the corresponding β,β-dichlorinated compound gave a remarkably stable radical cation.

Oxidative fusion reactions of meso-phenoxazino Ni(ii) porphyrin were found to be temperature dependent, giving rise to either a doubly phenylene-fused product at room temperature or a singly phenoxazine-fused product at 70 °C. The latter was further oxidized to a doubly phenoxazine-fused Ni(ii) porphyrin, which was subsequently converted to the corresponding free base porphyrin and Zn(ii) porphyrin. Compared to previously reported diphenylamine-fused porphyrins that displayed a molecular twist, doubly phenoxazine-fused porphyrins exhibited distinctly different properties owing to their highly planar structures, such as larger fluorescence quantum yields, formation of an offset face-to-face dimer both in solution and the solid state, and the generation of a mixed-valence π-radical cation dimer upon electrochemical oxidation. One-electron oxidation of the phenoxazine-fused Ni(ii) porphyrin with Magic Blue gave the corresponding radical cation, which was certainly stable and could be isolated by separation over a silica gel column but slowly chlorinated at the reactive β-positions in the solid state. This finding led to us to examine β,β′-dichlorinated phenoxazine-fused and diphenylamine-fused Ni(ii) porphyrins, which, upon treatment with Magic Blue, provided remarkably stable radical cations to an unprecedented level. It is actually possible to purify these radical cations by silica gel chromatography, and they can be stored for over 6 months without any sign of deterioration. Moreover, they exhibited no degradation even after the CH₂Cl₂ solution was washed with water. However, subtle structural differences (planar versus partly twisted) led to different crystal packing structures and solid-state magnetic properties.

On the association of neutral and cationic tris(tetrathiafulvaleno)dodecadehydro[18]annulenes

Here, we report the first X-ray crystal structure of a tetrathiafulvalene-fused dehydroannulene with peripheral ethylthio substituents. In addition, we have subjected this compound to electrochemical and UV-Vis-NIR/ESR spectroelectrochemical studies to elucidate the degree to which the oxidised species associate.