Novel Benzene-Bridged Triphenylene-Based Discotic Dyads

Ambipolar Charge Transport Properties of Naphthophenanthridine Discotic Liquid Crystals

A series of novel naphthophenanthridine derivatives are synthesized via N-annulation of hexabutoxytriphenylene-1-amine with various aliphatic aldehydes through the Pictet-Spengler reaction. The synthesized derivatives have been found to self-assemble into a columnar hexagonal mesophase over a wide temperature range, as validated through polarized optical microscopy, differential scanning calorimetry and X-ray diffraction experiments. The photophysical properties of these compounds were studied using UV-visible and emission spectroscopy. The synthesized compounds exhibit ambipolar charge transport, showing temperature-independent electron and hole mobility on the order of 3 × 10^-4 cm²/V s, as evaluated by the time-of-flight technique. These novel N-annulated derivatives can be of immense potential toward semiconducting applications of self-assembling supramolecular systems.

Supramolecular organogels based on mesogenic 2,7-difunctionalized triphenylenes as a simple system for water content assessment in light alcohols

Self-assembly of di-hydroxylated triphenylenes in columnar mesophases and organogels depends on the spacer length and allows water quantification in alcohols.

Phase Behavior of a New Class of Anthraquinone-Based Discotic Liquid Crystals

Five novel columnar liquid crystalline compounds (4.1-4.5) consisting of a central anthraquinone core carrying four alkoxy chains (R = n-C₆H₁₃, n-C₈H₁₇, n-C₁₀H₂₁, n-C₁₂H₂₅, and 3,7-dimethyl octyl) with two diagonally opposite 1-ethynyl-4-pentylbenzene units were synthesized, and their phase transitions were investigated between changes in the molecular structure and their self-assembly into the columnar mesophases. Small and wide-angle X-ray scattering (SAXS/WAXS) studies were performed to deduce the exact nature of the mesophases, and their corresponding electron density maps were derived from the intensities of the peaks observed in the diffraction patterns. A comparison of compounds with different alkoxy chains indicated that the soft crystal columnar rectangular (Cr_colrec) phase was stable at lower temperature for the shortest peripheral alkoxy chain (4.1; R = n-C₆H₁₃) and was found to exhibit the columnar hexagonal (Col_h) phase and then the discotic nematic (N_D) phase with increasing temperature. In contrast, increasing the peripheral chain length to n-C₈H₁₇ or the branched one (4.2 and 4.5) stabilized the Col_h phase at lower temperature and showed the N_D phase at higher temperature. Further increase in chain length (4.3 and 4.4; n-C₁₀H₂₁, n-C₁₂H₂₅) demonstrated the formation of the N_D phase. Conductivity measurement in the Col_h mesophase was found to be almost 10 times higher in magnitude than the corresponding Cr_colrec phase. The HOMO-LUMO band gap of all the compounds was found to be in the range from 2.79 to 2.82 eV, which is quite less and comparable with the optical energy band gap.

TNF Induced Switching of Columnar Rectangular to Hexagonal Assemblies in a New Class of Triphenylene-Based Room Temperature Discotic Liquid Crystals

A straightforward synthesis of triphenylene-based oligomeric systems that self-organize into room temperature columnar structures is presented. The compounds with longer spacer length (m = 10 and 12) exhibit columnar rectangular (Col_r) mesophase whereas the compound with m = 8 exists in glassy Col_r state. Interestingly, the Col_r self-assembly of these compounds switches to columnar hexagonal (Col_h) on doping the compounds with 2,4,7-trinitrofluorenone (TNF). For the dopant concentration of 1:1 with respect to native compound, an intermediate transition state between Col_r and Col_h phase was observed which completely transformed into the hexagonal phase on increasing the concentration to 1:2 (compound: TNF) and afterward. Both the Col_r and Col_h self-assemblies have been well resolved by detailed X-ray analysis. These kind of oligomeric compounds generally possess a combination of desirable alignment properties analogous to monomeric compounds and long-lived glassy states similar to that of polymeric mesogens. In addition, charge hopping behavior is expected to increase in these compounds due to donor-acceptor interactions. Overall, these compounds can find possible potential applications in semiconductor devices.

Electronic energy and electron transfer processes in photoexcited donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units

We investigate the photophysical properties of organic donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units linked by a non-conjugated flexible bridge in solution using complementary optical spectroscopy techniques. When these molecules are diluted in dichloromethane solution, energy transfer from the triphenylene to the perylene diimide excited moieties is evidenced by time-resolved fluorescence measurements resulting in a quenching of the emission from the triphenylene moieties. Simultaneously, another quenching process that affects the emission from both donor and acceptor units is observed. Solution ultrafast transient absorption measurements provide evidence of photo-induced charge transfer from either the donor or the acceptor depending upon the excitation. Overall, the analysis of the detailed time-resolved spectroscopic measurements carried out in the dyad and triad systems as well as in the triphenylene and perylene diimide units alone provides useful information both to better understand the relations between energy and charge transfer processes with molecular structures, and for the design of future functional dyad and triad architectures based on donor and acceptor moieties for organic optoelectronic applications.

Triphenylene discotic liquid crystal trimers synthesized by Co2(CO)8-catalyzed terminal alkyne [2 + 2 + 2] cycloaddition

The synthesis of star-shaped discotic liquid crystal trimers using Co₂(CO)₈-catalyzed terminal alkyne [2 + 2 + 2] cycloaddition reaction is reported. The trimers consist of three triphenylene discotic units linked to a central 1,2,4-trisubstituted benzene ring via flexible spacers. The trimers were synthesized in the yields up to 70% by mixing the monomers with 10 mol % of Co₂(CO)₈ as the catalyst in refluxing 1,4-dioxane. The liquid crystalline properties were investigated by using polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Trimer 4 with an ester connecting group and a longer spacer exhibited a rectangular columnar mesophase, while 5b and 5c possessing an ether linkage and a shorter spacer display a hexagonal columnar mesophase. The connecting functional group and the length of the flexible spacer between the central benzene ring and the triphenylene units have pivotal influence on the mesomorphism.