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Two series of discotic columnar liquid crystals were prepared and investigated, consisting of a triazine core to which three triphenylenes (HATs) are attached, connected via a flexible variable spacer containing a triazole group. The triphenylenes have five pentafluoropentyloxy tails or four pentafluoropentyloxy tails and one methoxy group. The compounds with four fluorinated tails on the HAT groups show a lamellar-columnar phase (Collam), whereas a compound with five fluorinated tails on the HAT groups shows a hexagonal-columnar (Colh) phase. Small differences in the steric properties and fluorophobic effects can therefore have a strong influence on the ordering of the molecules in the liquid crystalline phase.

Two new series of columnar discotic liquid crystalline materials based on a tristriazolotriazine (TTT) core connected to three pendant hexyloxytriphenylene or pentafluoropentyloxytriphenylene groups via a flexible alkyl spacer are synthesised and investigated. It is found that the mesophase stability is very much dependent on the spacer length. For a short spacer length (propyl or butyl), Colh phases are found in which the disc-like moieties are randomly mixed in the columns. For one compound with a pentyl spacer and pentafluoropentyloxy tails on the triphenylene groups, a Colob phase is found in which the columns of triphenylenes and TTT moieties are separated. When the spacer is longer (hexyl), the liquid crystallinity is lost. The compounds with pentafluoropentyloxy tails on the triphenylene units have a higher thermal stability than those with hexyloxy tails.

A series of novel discotic liquid crystal compounds containing three pendent triphenylenes connected to a triazine core via spacers of different length that were linked via a triazole group as obtained from an azide–alkyne click reaction was investigated. All compounds of the series exhibit wide-range columnar phases from room temperature to more than 100°C. X-ray reflection measurements indicate an ordering with separate columns of the triazine and triphenylene cores. Quantum chemical calculations confirmed the significant contributions of the triazine and triazole groups to the p–p stacking in the columns. This type of organisation reveals an additional feature of triazole-forming click chemistry and indicates interesting properties for optoelectronic applications.

The microscopic origin of the bright nanosecond blue-green photoluminescence (PL), frequently reported for synthesized organically terminated Si quantum dots (Si-QDs), has not been fully resolved, hampering potential applications of this interesting material. Here a comprehensive study of the PL from alkyl-terminated Si-QDs of 2-3 nm size, prepared by wet chemical synthesis is reported. Results obtained on the ensemble and those from the single nano-object level are compared, and they provide conclusive evidence that efficient and tunable emission arises due to radiative recombination of electron-hole pairs confined in the Si-QDs. This understanding paves the way towards applications of chemical synthesis for the development of Si-QDs with tunable sizes and bandgaps.

Silica is a prominently utilized heterogeneous metal catalyst support. Functionalization of the silica with poly(ether imine) based dendritic phosphine ligand was conducted, in order to assess the efficacy of the dendritic phosphine in reactions facilitated by a silica supported metal catalyst. The phosphinated poly(ether imine) (PETIM) dendritic ligand was bound covalently to the functionalized silica. For this purpose, the phosphinated dendritic ligand containing an amine at the focal point was synthesized initially. Complexation of the dendritic phosphine functionalized silica with Pd(COD)Cl-2 yielded Pd(II) complex, which was reduced subsequently to Pd(0), by conditioning with EtOH. The Pd metal nanoparticle thus formed was characterized by physical methods, and the spherical nanoparticles were found to have >85% size distribution between 2 nm and 4 nm. The metal nanoparticle was tested as a hydrogenation catalyst of olefins. The catalyst could be recovered and recycled more than 10 times, without a loss in the catalytic efficiency.

The synthesis and liquid crystalline properties of two novel series of triphenylenes with 4 or 5 pentafuoropentyloxy tails and 1 or 2 alkoxy tails of varying length are reported. All compounds form wide-range hexagonal columnar phases. The isotropisation temperatures and the corresponding enthalpy changes for the compounds with 4 or 5 fluorinated tails are higher than for the compounds with 6 alkoxy tails, and also higher than for compounds with 6 fluorinated tails. These results indicate that the best ordering is obtained for compounds with a mix of fluorinated and non-fluorinated tails. With increasing length of the alkyl tails in HAT compounds with 4 or 5 fluoroalkoxy tails, the isotropisation temperatures decrease and the d-spacings as observed by XRD increase. All fluoro-containing compounds have a strong tendency for spontaneous homeotropic alignment on surfaces, both hydrophilic and hydrophobic.

Colloidal semiconductor quantum dots (QDs) constitute a perfect material for ink-jet printable large area displays, photovoltaics, light-emitting diode, bio-imaging luminescent markers and many other applications. For this purpose, efficient light emission/absorption and spectral tunability are necessary conditions. These are currently fulfilled by the direct bandgap materials. Si-QDs could offer the solution to major hurdles posed by these materials, namely, toxicity (e.g., Cd-, Pb- or As-based QDs), scarcity (e.g., QD with In, Se, Te) and/or instability. Here we show that by combining quantum confinement with dedicated surface engineering, the biggest drawback of Si—the indirect bandgap nature—can be overcome, and a ‘direct bandgap’ variety of Si-QDs is created. We demonstrate this transformation on chemically synthesized Si-QDs using state-of-the-art optical spectroscopy and theoretical modelling. The carbon surface termination gives rise to drastic modification in electron and hole wavefunctions and radiative transitions between the lowest excited states of electron and hole attain ‘direct bandgap-like’ (phonon-less) character. This results in efficient fast emission, tunable within the visible spectral range by QD size. These findings are fully justified within a tight-binding theoretical model. When the C surface termination is replaced by oxygen, the emission is converted into the well-known red luminescence, with microsecond decay and limited spectral tunability. In that way, the ‘direct bandgap’ Si-QDs convert into the ‘traditional’ indirect bandgap form, thoroughly investigated in the past. Keywords: direct bandgap; optical spectroscopy; optoelectronics; organic capping; silicon quantum dots; tight binding model

Hydroxyl group terminated poly(propyl ether imine) dendrimers of 1 to 5 generations absorb in the region of 260-340 nm, in MeOH and aqueous solutions. Excitation of a solution of the dendrimers at 330 nm led to an emission at approximately 390 nm. The emission intensities increased under acidic pH and in more viscous solvents. The presence of air did not affect the emission profiles, as also aging of a dendrimer solution for prolonged periods. Lifetime measurements show at least two species responsible for the emission. Anions perchlorate, periodate, nitrite, and pyridinium methyliodide quenched the fluorescence efficiently, among several anions tested.