Multibromo-N-alkylcarbazoles: synthesis, characterization, and their benzo[b]thiophene derivatives

A Carbazole-Bridged Biscyclometalated Diplatinum Complex: Synthesis, Characterization, and Dual-Mode Aggregation-Enhanced Phosphorescence

A cationic carbazole-bridged biscyclometalated diplatinum complex 4 has been synthesized and characterized. Single-crystal X-ray analysis demonstrates that complex 4 displays a dimeric structure with noncovalent π-π stacking and unique double Pt-Pt interactions. In aerated dilute CH₃CN, complex 4 is characterized by a very weak monomeric yellow emission (λ_emi = 547 nm; Φ = 0.51%), which is attributed to the triplet intraligand (³LC) excited state mixing with some charge transfer characters. In contrast, under aerated conditions, the dispersion of 4 in a mixed solvent of CH₃CN/Et₂O (1/9, v/v) or CH₃CN/H₂O (1/9, v/v) displays intense yellow (λ_emi = 550 nm; Φ = 35.5%; τ = 11.10 μs) and red emission (λ_emi = 635 nm; Φ = 14.1%; τ = 7.00 μs), respectively. These aggregation-induced phosphorescent emission enhancements are considered being caused by the oxygen-shielding effect and the molecular rigidification-induced decrease of nonradiative decays in the aggregate state. The morphology and size of the aggregates under these two conditions are examined by scanning electron microscope and dynamic light scattering analysis. The absorption and emission properties of 4 are further rationalized by time-dependent density functional theory calculations on a model compound.

Synthesis and biological studies of amphiphilic carbazole pyridinium conjugates

Amphiphilic carbazole pyridinium conjugates are synthesized and characterized by IR, 1H and [Formula: see text]C NMR and ESI-MS spectrometry. The pyridinium group is attached on the 3-position of the carbazole ring and long alkyl chains are linked to the central [Formula: see text] atom. The introduction of a pyridinium group afforded water-soluble carbazole derivatives with significant bathochromic shifts in their absorption and emission spectra. As compared to the parent [Formula: see text]-butylcarbazole compound, carbazole pyridinium conjugates exhibited 50 nm red-shifted absorption maxima. Similarly, the carbazole pyridinium conjugates displayed 143–147 nm red-shifted emission maxima in solution. In addition, large Stokes shifts (5747–7558 cm[Formula: see text] were observed for the conjugates in solution. The cell penetrable amphiphilic carbazole pyridinium conjugates exhibited cytoplasmic distribution in A549 cells.

Tuning the Photophysical and Electroluminescence Properties in Asymmetrically Tetrasubstituted Bipolar Carbazoles by Functional Group Disposition

Carbazoles decorated with both donor and acceptor fragments offer a classical way to optimize bipolar functional properties. In this work, a series of carbazoles featuring triphenylamine donors and cyano acceptors are synthesized and their structure-property relationship is studied. The effects of connectivity and the chromophore number density on photophysical and electroluminescence properties are investigated. The position of the triphenylamine donor on the 3,6-dicyanocarbazole nucleus significantly affected the photophysical and electroluminescence properties. The dye possessing triphenylamine on C2 and C7 displayed a red shift in absorption when compared with the structural analogue with triphenylamine tethered to C1 and C8. The emission wavelength of the dyes are tunable from blue to green, by altering the position of triphenylamine and cyano substituents. All of the dyes exhibited positive solvatochromism in emission, attributable to the photoinduced intramolecular charge transfer from the triphenylamine donor to the cyano acceptor. However, the extent of charge transfer and hybridization of local and charge-transfer-excited states is highly dependent on the position of triphenylamine and cyano groups on the carbazole nucleus. Dyes containing cyano substituents at C2 and C7 showed a prolonged excited state lifetime, broad emission, and large Stokes shifts, indicating the presence of a higher charge transfer component in the excited state. The dyes displayed exceptional thermal stability with the onset decomposition temperature (10% weight loss) > 350 °C. Electrochemical measurements revealed low oxidation potential for dyes containing triphenylamine at C3 and/or C6. Addition of a cyano acceptor on carbazole led to the stabilization of lowest unoccupied molecular orbital. Furthermore, the materials were tested as emitting dopants in solution-processable multilayer organic light emitting diodes and found to display deep-blue/sky-blue electroluminescence with external quantum efficiency as high as 6.5% for a deep-blue emitter (CIE y ∼ 0.06).

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

Modulation of aggregation-induced emission and electroluminescence of silole derivatives by a covalent bonding pattern

The deciphering of structure-property relationships is of high importance to rational design of functional molecules and to explore their potential applications. In this work, a series of silole derivatives substituted with benzo[b]thiophene (BT) at the 2,5-positions of the silole ring are synthesized and characterized. The experimental investigation reveals that the covalent bonding through the 2-position of BT (2-BT) with silole ring allows a better conjugation of the backbone than that achieved though the 5-position of BT (5-BT), and results in totally different emission behaviors. The silole derivatives with 5-BT groups are weakly fluorescent in solutions, but are induced to emit intensely in aggregates, presenting excellent aggregation-induced emission (AIE) characteristics. Those with 2-BT groups can fluoresce more strongly in solutions, but no obvious emission enhancements are found in aggregates, suggesting they are not AIE-active. Theoretical calculations disclose that the good conjugation lowers the rotational motions of BT groups, which enables the molecules to emit more efficiently in solutions. But the well-conjugated planar backbone is prone to form strong intermoelcular interactions in aggregates, which decreases the emission efficiency. Non-doped organic light-emitting diodes (OLEDs) are fabricated by using these siloles as emitters. AIE-active silole derivatives show much better elecroluminescence properties than those without the AIE characterisic, demonstrating the advantage of AIE-active emitters in OLED applications.