A series of cyanine fluorophores based on fused aromatics as an electron donor for DNA sensing and two-photon bioimaging were synthesized, among which the carbazole-based biscyanine exhibits high sensitivity and efficiency as a fluorescent light-up probe for dsDNA, which shows selective binding toward the AT-rich regions. The synergetic effect of the bischromophoric skeleton gives a several-fold enhancement in a two-photon absorption cross-section as well as a 25- to 100-fold enhancement in two-photon excited fluorescence upon dsDNA binding.
Organic and polymeric photovoltaic (PV) cells show promise as low-cost, lightweight, flexible, and renewable energy sources and have been extensively investigated during the past decade. [1] Recently, tremendous progress was made in the development of bulk heterojunction organic PV cells based on p-conjugated polymers as electron donor ( p-type) materials, i.e., regioregular poly(3-alkylthiophene)s (P3HTs), blended with soluble fullerenes (C 60 ) as electron acceptor (n-type) materials, i.e., [6,6]-phenyl C 61 -butyric acid methyl ester (PCBM). With an accurate control of the formation of the nanostructure of the interpenetrating donor/acceptor polymer network by means of limiting the solvent evaporation rate or by post-fabrication thermal annealing, power conversion efficiencies (PCE) greater than 5% were achieved.[2] Meanwhile, multilayer heterojunction PV cells that are based on small molecules also advanced significantly through the use of new optimized device architectures, e.g., tandem or dual dye-doped structures, with efficiencies reportedly being as high as 5.6%. [3] However, in order to further enhance the PCEs of heterojunction PV cells it is of paramount importance to develop novel organic and polymer semiconductors exhibiting a narrow optical gap as well as a high charge carrier mobility to harvest the majority of sunlight radiation and efficiently transport the photogenerated charges to the electrodes. [1d,e] Triarylamines, which are well-known to have high holetransport mobilities and form stable cation radicals, are widely used as hole-transporting materials in organic light emitting diodes (LED), [4] and show potential as molecular based magnets. [5] Recently, it was demonstrated that light emitting molecules/ polymers which are incorporated or end-capped with diarylamine/triarylamine moieties exhibit a greatly enhanced LED device performance. [6] In order to further improve the light harvesting efficiency of a hole-transporting triarylamine, hence enable its efficient application in photovoltaics, it is necessary to reduce its optical energy gap to better match the solar spectrum. The use of electron-accepting dicyanovinyl groups to introduce the low-lying LUMO of triarylamine derivatives into p-type semiconducting star-shaped molecules thereby reducing the optical energy gap has been reported.[7]Herein, we report the synthesis and characterization of novel hole-transporting and narrow HOMO-LUMO energy gap oligothiophenes that are asymmetrically endcapped with diphenylaminofluorenyl and dicyanovinyl groups, i.e., PhN-OFOT(n)-DCN (n ¼ 2-4), and their potential for photovoltaic applications. The incorporation of triarylamino-donors and dicyanovinylacceptors greatly reduces the optical energy gap of oligothiophene thin-films to 1.82-1.92 eV, while the first ionization energy remains high with $5.2 eV, which is important in obtaining high open-circuit voltages (V oc ) as well as improving air stability. An increase in oligothiophene length provides stronger light absorption and promotes better ...
A novel homologues series of diphenylamino and 1,2,4-triazole endcapped pi-conjugated oligofluorenes has been synthesized using palladium-catalyzed Suzuki cross-coupling of 9,9-dibutyl-7-(diphenylamino)-2-fluorenylboronic acid, and 1,2,4,-triazole-substituted oligofluorenyl halide was used as a key step. Efficient two- and three-photon excited photoluminescence and lasing were obtained by pumping with near-infrared femto-second lasers. The three-photon absorption cross-section enhances significantly up to 2.48 x 10(-78) cm(6) s(2) in the femtosecond regime with the length of the conjugation system. The emission is in the deep blue region and the best full width half-maximum (fwhm) of the three-photon lasing is narrower than 6 nm which is the narrowest ever reported. It was also shown that the nonlinear optics (NLO) effect increased parabolically with the conjugation length but without changing the emission wavelength. This demonstrates that varying the conjugation length is a very effective way to tailor an OF-based NLO device for deep blue application. Our findings open a new avenue to design highly efficient multiphoton absorption molecules for photoluminescence and lasing as well as provide a novel series of organic molecules that can be used in NLO applications and fundamental study.
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