Triindole-Bridge-Triindole Dimers as Models for Two Dimensional Microporous Polymers

New dimers with two triindole subunits bound together through different linkers (<i>p</i>-phenylene or diacetylene groups) have been synthesized and studied as model systems to determine the differences in the electron transfer ability of the two bridging units. Our results show that whereas a <i>p</i>-phenylene bridge nearly isolates the two subunits of the dimers a diacetylene bridge allows a high level of electronic connection between them

Symmetry Lowering in Triindoles: Impact on the Electronic and Photophysical Properties

The electronic and photophysical properties of 6,11-dihydro-5<i>H</i>-diindolo­[2,3-<i>a</i>:2′,3′-<i>c</i>]­carbazole, an asymmetric cyclic dehydrotrimer of indole, have been explored and compared to its symmetric analogue, 10,15-dihydro-5<i>H</i>-diindolo­[3,2-<i>a</i>:3′,2′-<i>c</i>]­carbazole (triindole), a well-known high hole mobility semiconductor. To this purpose, we use a joint experimental and theoretical approach that combines absorption and emission spectroscopies, cyclic voltammetry, and spectroelectrochemistry with DFT calculations. Lowering the symmetry of the triindole platform causes a red-shift of the absorption edge and emission maxima and improved the fluorescence quantum yield. Cyclic voltammetry and spectroelectrochemistry reveal the reversible nature of the two observable oxidation processes in the alkylated asymmetric triindoles together with an increase in the stabillity of their oxidized species. On the other hand, the insertion of alkyl groups on the nitrogen atoms results in a further fluorescence enhancement although larger reorganization energies are found. DFT and time-dependent (TD-DFT) calculations successfully support the experimental data and aid in the understanding of the tuning of the physicochemical properties of the triindole platform upon symmetry lowering toward their incorporation in electronic devices

Mobility versus Alignment of a Semiconducting π‑Extended Discotic Liquid-Crystalline Triindole

The p-type semiconducting properties of a triphenylene-fused triindole mesogen, have been studied by applying two complementary methods which have different alignment requirements. The attachment of only three flexible alkyl chains to the nitrogen atoms of this π-extended core is sufficient to induce columnar mesomorphism. High hole mobility values (0.65 cm² V^–1 s^–1) have been estimated by space-charge limited current (SCLC) measurements in a diode-like structure which are easily prepared from the melt, rendering this material a good candidate for OPVs and OLEDs devices. The mobility predicted theoretically via a hole-hopping mechanism is in very good agreement with the experimental values determined at the SCLC regime. On the other hand the hole mobility determined on solution processed thin film transistors (OFETs) is significantly lower, which can be rationalized by the high tendency of these large molecules to align on surfaces with their extended π-conjugated core parallel to the substrate as demonstrated by SERS. Despite the differences obtained with the two methods, the acceptable performance found on OFETs fabricated by simple drop-casting processing of such an enlarged aromatic core is remarkable and suggests facile hopping between neighboring molecular columns owing to the large conducting/isolating ratio found in this discotic compound