Expanded porphyrin-like structures based on twinned triphenylenes.

Triphenylene twins are intriguing structures, and those bridged through their 3,6-positions by dipyrromethene units give a new class of macrocycles that can be viewed as rigid, expanded porphyrin derivatives in which coplanarity is enforced in a formally antiaromatic π system. Somewhat surprisingly, however, macrocyclization leads to significant overall stabilization of the dipyrromethene chromophores.

Prediction of EPR spectra of liquid crystals with doped spin probes from fully atomistic molecular dynamics simulations: exploring molecular order and dynamics at the phase transition.

Liquid crystals spin their secrets: Electron paramagnetic resonance (EPR) spectra are predicted directly and completely from fully atomistic molecular dynamics (MD) simulations of 4-cyano-4-n-pentylbiphenyl (5CB) nematic liquid crystals with a doped nitroxide spin probe (depicted in yellow; red curve = simulated and blue curve = measured EPR spectrum).

Muon spin spectroscopy of the discotic liquid crystal HAT6.

Avoided level crossing muon spin resonance (ALC-muSR) has been used to study the cyclohexadienyl-type radicals produced by the addition of muonium (Mu) to the discotic liquid crystal HAT6 (2,3,6,7,10,11-hexahexyloxytriphenylene) in the crystalline (Cr) phase, the hexagonal columnar mesophase (Col(h)) and isotropic (I) phase. In the Cr phase unpaired electron spin density can be transferred from the radical to neighboring HAT6 molecules depending on the overlap of their pi-systems and hence on the relative orientation of the triphenylene rings. The two Delta(1) resonances in the ALC-muSR spectra of the Cr phase indicate that the neighboring HAT6 molecules have two preferred orientations with respect to the radical: one which results in negligible spin density transfer and a second where 17% of the unpaired spin density is transferred. The ALC-muSR spectra in Col(h) and I phases are substantially different from those of the Cr phase in that there are two narrow resonances superimposed on an extremely broad and intense resonance. The narrow resonances are due to highly mobile radicals located in the aliphatic region between the columns and the broad resonance is due to radicals incorporated within the columns of HAT6 molecules. The large width and amplitude of this resonance indicates that the radicals within the columns are undergoing rapid electron spin relaxation but the mechanism that causes this relaxation is unknown.

A bromine catalysed dimerisation of alpha,alpha'-dihalomonopyrrolo-TTF.

Dihalomonopyrrolo-TTF undergoes a bromine catalysed dimerisation reaction to yield a novel type of extended TTF derivative.

Aryl trihydroxyborates: easily isolated discrete species convenient for direct application in coupling reactions.

A conceptually and practically simple alternative approach to the use of arylboron species as the organometallic component in cross-coupling processes is described whereby trihydroxyborate salts are isolated and directly employed. The protocol derives practical benefit from the ease and convenience of the isolation and subsequent use of the discrete borate salts, eliminates the need for additional base, and aids the use of correct reaction stoichiometry.

Macrodiscotic triphenylenophthalocyanines.

The first heavily substituted triphenylenophthalocyanines have been synthesised and found to be mesogenic.

Muoniated spin probes in the discotic liquid crystal HHTT: rapid electron spin relaxation in the hexagonal columnar and isotropic phases.

Avoided level crossing muon spin resonance (ALC-µSR) spectroscopy was used to study radicals produced by the addition of the light hydrogen isotope muonium (Mu) to the discotic liquid crystal (DLC) 2,3,6,7,10,11-hexahexylthiotriphenylene (HHTT). Mu adds to the secondary carbon atoms of HHTT to produce a substituted cyclohexadienyl radical, whose identity was confirmed by comparing the measured hyperfine coupling constants with values obtained from DFT calculations. ALC-µSR spectra were obtained in the isotropic (I), hexagonal columnar (Col(h)), helical (H), and crystalline (Cr) phases. In the I and Col(h) phases the radicals, which are incorporated within the stacks of HHTT molecules as isolated paramagnetic defects, undergo extremely rapid electron spin relaxation, on the order of a hundredfold faster than in the H or Cr phases. The electron spin relaxation rate increases significantly with increasing temperature and appears to be caused by the liquidlike motion within the columns, which modulates the overlap between the π system of the radical and the π systems of the neighboring HHTT molecules, and hence, the hyperfine coupling constants. Rapid electron spin relaxation should occur for any π radical incorporated within the columns of a DLC, which may limit the utility of DLCs for future spin-based technologies.

Unexpected phenol production from arylboronic acids under palladium-free conditions; organocatalyzed air oxidation.

An intriguing class of quinones that efficiently catalyze the air oxidation (overall hydroxylation) of arylboronic acids to the corresponding phenol is reported. Autocatalysis in the parent system is particularly efficient and leads to rapid, quantitative synthesis of quinones such as 4 from boronic acid 1 at room temperature using air as stoichiometric oxidant. The efficiency results from a balance between two-stage conjugate addition and migration with each step driven by aromatization of a naphthalene fragment.

Synthesis of crown ether-linked discotic triphenylenes.

Novel triphenylene dimers linked by a central crown ether core have been synthesized and characterized. The crown ether is most conveniently formed as a final step to permit purification and isolation of ion-free material, and extension of the protocol permits synthesis of triad structures linked though a 27-crown-9 macrocycle. The latter compounds present a new discotic motif that supports mesophase formation.

Antiaromatic twinned triphenylene discotics showing nematic phases and 2-dimensional pi-overlap in the solid state.

Construction of formally antiaromatic discotic twins based on dehydroannulene cores linked through non-adjacent positions on triphenylenes gives stable molecules with intriguing molecular and supramolecular properties and, unlike the majority of discotic triphenylenes and similar materials, the twins form nematic mesophases on heating.

Probing the structural factors influencing columnar mesophase formation and stability in triphenylene discotics.

Series of structurally related substituted triphenylene derivatives were designed and synthesised to interrogate key features which determine mesophase formation and stability, and to challenge the general conclusions previously proposed by us and others. It is apparent that no single, simple principle can be universally applied.

Perylenophthalocyanines.

The first perylenophthalocyanines have been synthesised using a Diels-Alder reaction between dialkylperylenes and fumaronitrile as the key step towards the dinitrile precursors. As expected the octaalkylperylenophthalocyanines show red-shifted absorption spectra. They are high melting solids that do not display mesophase behaviour at accessible temperatures. A 3:1 phthalocyanine/perylenophthalocyanine hybrid material, prepared by a mixed macrocyclisation reaction, presents an unusual board-like molecular profile. Its absorption maxima lie between those observed for the parent phthalocyanines and the symmetrical perylenophthalocyanines. The spectrum shows a characteristic split Q-band due to the reduced symmetry of the core. This material is non-mesogenic but is sufficiently soluble to permit processing and characterisation. The (1)H NMR spectrum indicates that at least two of the appended alkyl chains are displaced out of the macrocycle plane and lie in its shielding region--an arrangement that disfavours the face-to-face packing required for mesophase formation.