Thermally Stable Nonaggregating Pyrenylarenes for Blue Organic Light-Emitting DevicesCDRI communication No. 8097

Synthesis and Properties of 4- and 10-Benzoyl-1-azapyrenes

A series of 4- and 10-benzoyl-1-azapyrenes were prepared by a combination of Pd-catalyzed cross-coupling reactions and Brønsted-acid-mediated alkyne-carbonyl-metathesis (ACM). The photophysical and electrochemical properties of the products were studied and compared to theoretical results.

Synthesis of Solution-Processable Donor-Acceptor Pyranone Dyads for White Organic Light-Emitting Devices

A series of donor-acceptor pyranones (3a-m, 4a-h) were synthesized using α-oxo-ketene- S, S-acetal as the synthon for their application as emissive materials for energy-saving organic light-emitting devices (OLEDs). Among them, five pyranones 3f, 3g, 3h, 3m, and 4e exhibited highly bright fluorescence in the solid state and weak or no emission in the solution state. Photophysical analysis of these dyes revealed that only 3f and 3m showed aggregation-induced emission behavior in a THF/water mixture (0-99%) with varying water fractions ( f_w) leading to bright fluorescence covering the entire visible region, while other derivatives 3g, 3h, and 4e did not show any fluorescence signal. The computational studies of the compounds revealed that the longer wavelength absorption originates from HOMO to LUMO electronic excitation. These dyes exhibited good thermal stability with 5% weight loss temperature in the range of 218-347 °C. The potential application of the donor-acceptor pyranone dyads was demonstrated by fabrication of solution-processed OLEDs. Remarkably, OLED devices prepared using highly emissive compounds 6-(anthracen-9-yl)-4-(methylthio)-2-oxo-2 H-pyran-3-carbonitrile (3m) and 6-(4-methoxyphenyl)-4-(methylthio)-2-oxo-2 H-pyran-3-carbonitrile (3f) displayed pure white emission with CIE coordinates of (0.29, 0.31) and (0.32, 0.32), respectively. Additionally, the resultant devices exhibited external quantum efficiencies of 1.9 and 1.2% at 100 cd m^-2, respectively.

Base-Promoted Selective Synthesis of 2H-Pyranones and Tetrahydronaphthalenes via Domino Reactions

A highly efficient domino protocol has been developed for the synthesis of 6-aryl-4-(methylthio/amine-1-yl)-2-oxo-2H-pyran-3-carbonitriles and 4-aryl-2-(amine-1-yl)-5,6,7,8-tetrahydronaphthalene-1-carbonitriles from simple and readily available α-aroylketene dithioacetals, malononitrile, secondary amines, and cyclohexanone. This elegant domino process involved consecutive addition-elimination, intramolecular cyclization, and ring opening and closing sequences. Notably, in situ generated 2-imino-4-(methylthio/amine-1-yl)-6-aryl-2H-pyran-3-carbonitrile plays multiple roles in the construction of various novel polyaromatic hydrocarbons.

A new type of biocompatible fluorescent probe AFN for fixed and live cell imaging of intracellular lipid droplets

We discovered a new type of nontoxic, highly fluorogenic and biocompatible probe AFN for selective staining of intracellular Lipid Droplets (LDs) in both fixed and live human cervical cancer cells (HeLa) and 3T3-L1 pre-adipocytes without any background artifacts.

Synthesis, physical and electroluminescence properties of 3,6-dipyrenylcarbazole end capped oligofluorenes

A series of oligofluorenes bearing 3,6-dipyrenylcarbazoles as the terminal substituents showed strong blue emission with good solubility, and thermally stable amorphous and excellent film-forming properties. OLEDs using these materials exhibited excellent device performance.

Discovery of biaryl-4-carbonitriles as antihyperglycemic agents that may act through AMPK-p38 MAPK pathway

A series of functionalized biaryl-4-carbonitriles was synthesized in three steps and evaluated for PTP-1B inhibitory activity. Among the synthesized compounds, four biaryls 6a-d showed inhibition (IC50 58-75 μM) against in vitro PTP-1B assay possibly due to interaction with amino acid residues Lys120, Tyr46 through hydrogen bonding and aromatic-aromatic interactions, respectively. Two biaryl-4-carbonitriles 6b and 6c showed improved glucose tolerance, fasting as well as postprandial blood glucose, serum total triglycerides, and increased high-density lipoprotein-cholesterol in SLM, STZ, STZ-S and C57BL/KsJ-db/db animal models. The bioanalysis of 4'-bromo-2,3-dimethyl-5-(piperidin-1-yl)biphenyl-4-carbonitrile (6b) revealed that like insulin, it increased 2-deoxyglucose uptake in skeletal muscle cells (L6 and C2C12 myotubes). The compound 6b significantly up-regulated the genes related to the insulin signaling pathways like AMPK, MAPK including glucose transporter-4 (GLUT-4) gene in muscle tissue of C57BL/KsJ-db/db mice. Furthermore, it was observed that the compound 6b up-regulated PPARα, UCP2 and HNF4α, which are key regulator of glucose, lipid, and fatty acid metabolism. Western blot analysis of the compound 6b showed that it significantly increased the phosphorylation of AMPK and p38 MAPK and ameliorated glucose uptake in C57BL/KsJ-db/db mice through the AMPK-p38 MAPK pathway.

Diversity-oriented general protocol for the synthesis of privileged oxygen scaffolds: pyrones, coumarins, benzocoumarins and naphthocoumarins

A new general methodology for the synthesis of various functionalized privileged oxygen heterocyclic scaffolds, viz. pyrones, coumarins, and benzannulated coumarins, is developed. The synthesis proceeds through carbanion-induced ring transformation of lactones with various methylene carbonyl compounds followed by DDQ-mediated unprecedented oxidative cleavage of oxaylidenes intermediates. Studies of the mechanism of the conversions of oxaylidene intermediates into corresponding carbonyl compounds in the presence of DDQ revealed that the reactions took place via the formation of a Michael adduct instead of an intermolecular charge transfer complex. The methodology offers the fabrication of diverse privileged scaffolds with tolerance for many functional groups onto the oxygen heterocyclic molecular framework.

Recent developments of ketene dithioacetal chemistry

Ketene dithioacetals are versatile intermediates in organic synthesis. Extensive research, since the last decade, has given rise to new prospects in their chemistry. The objective of this review is twofold: first, to highlight the new prospects in the chemistry of functionalized ketene dithioacetals, and second, to provide an intrinsic link between ketene dithioacetal groups and a variety of other functional groups, which has brought out many new facts that will assist in future designs.

Fluorescence enhancement of pyrene chromophores induced by alkyl groups through σ-π conjugation: systematic synthesis of primary, secondary, and tertiary alkylated pyrenes at the 1, 3, 6, and 8 positions and their photophysical properties

We have systematically synthesized 1-, 3-, 6-, and 8-alkyl-substituted pyrene derivatives using the latest synthesis methods and investigated the effects of alkyl substitution on the photophysical properties of the pyrene chromophore. Like the trimethylsilyl group, which is known to enhance the fluorescence properties of some chromophores through σ*-π* conjugation, alkyl groups (primary, secondary, and tertiary) enhanced the fluorescence quantum yield of the pyrene chromophore through σ-π conjugation in most cases. While these enhancements in the fluorescence quantum yield were beyond expectations, the results were supported by absolute measurements. These results also indicate that ubiquitous alkyl groups can be used to tune the photophysical properties of the pyrene chromophore, as well as to improve the solubility or prevent aggregation. In other words, they can be used to develop new photofunctional materials.

Additional insights into luminescence process of polycyclic aromatic hydrocarbons with carbonyl groups: photophysical properties of secondary N-alkyl and tertiary n,n-dialkyl carboxamides of naphthalene, anthracene, and pyrene

Here we report the substitution effects of N-alkyl and N,N-dialkyl carboxamide groups on the fluorescence properties of polycyclic aromatic hydrocarbon chromophores, so as to control their fluorescence properties. The fluorescence properties of compounds obtained using solvents with different polarities showed very little change, indicating that the modified compounds do not form charge transfer states. TD-DFT calculations and measurements performed at low temperature (78 K) and in viscous solvents revealed that the N-alkyl and N,N-dialkyl carboxamide groups tend to reduce the contributions from intersystem crossing and increase those from internal conversion. Considering that the fluorescence mechanism of low-fluorescence carbonyl compounds such as aldehyde and ketone is dominated by intersystem crossing and that of high-luminescence carbonyl compounds such as carboxylic acid and ester is dominated by a radiative process, it can be said that the photophysical process of N-alkyl and N,N-dialkyl carboxamides is novel. In addition, the calculation results for excited states indicated that such contributions can be controlled by selecting the appropriate polycyclic aromatic hydrocarbon or amide structure, in addition to solvent viscosity and temperature.