Star-shaped charge-transporting materials with a triphenylamine (TPA) core and various phenylethenyl side arm(s) were obtained in a one-step synthetic procedure from commercially available and relatively inexpensive starting materials. Crystallinity, glass-transition temperature, size of the π-conjugated system, energy levels, and the way molecules pack in the solid state can be significantly influenced by variation of the structure of these side arm(s). An increase in the number of phenylethenyl side arms was found to hinder intramolecular motions of the TPA core, and thereby provide significant enhancement of the fluorescence quantum yield of the TPA derivatives in solution. On the other hand, a larger number of side arms facilitated exciton migration through the dense side-arm network formed in the solid state and, thus, considerably reduces fluorescence efficiency by migration-assisted nonradiative relaxation. This dense network enables charges to move more rapidly through the hole-transport material layer, which results in very good charge drift mobility (μ up to 0.017 cm(2) V (-1) s(-1)).
A series of neutral long-lived purely organic radicals based on the stable [4-(N-carbazolyl)-2,6-dichlorophenyl]bis(2,4,6-trichlorophenyl)methyl radical adduct (Cbz-TTM) is reported herein. All compounds exhibit ambipolar charge-transport properties under ambient conditions owing to their radical character. High electron and hole mobilities up to 10 and 10 cm V s , respectively, were achieved. Xerographic single-layered photoreceptors were fabricated from the radicals studied herein, exhibiting good xerographic photosensitivity across the visible spectrum.
A series of N‐alkylcarbazol‐3,6‐diyl trimers and pentamers has been synthesized by stepwise Suzuki coupling. The trimers with isopropyl and longer alkyl substituents at the nitrogen atom and all the pentamers form stable glasses with glass transition temperatures varying from 30 to 148 °C for the trimers and 65 to 104 °C for the pentamers. The ionization potential of the N‐alkylcarbazol‐3,6‐diyl trimers is 5.25 eV and 5.20 eV for the pentamers. N‐alkylcarbazol‐3,6‐diyl compounds typically exhibit hole‐drift mobilities in the range of 10−4–10−6 cm2 · V−1 · s−1. The highest hole‐drift mobility observed in an amorphous film of N‐octylcarbazol‐3,6‐diyl pentamer reached 10−3 cm2 · V−1 · s−1 at an applied electric field of 8.1 × 105 V · cm−1.
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Stable radical adducts of the TTM series bearing carbazolyl or indolyl fragments show bipolar transport properties with mobility values among the highest detected in glassy small molecules. Bipolarity is attributed to the radical character, while the heterocyclic ring confers the adducts the glassy morphological states and the non-dispersive regimes for charge transport.
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