An improved synthetic approach was developed for the synthesis of 1,4‐bis[9′,9′‐bis(6″‐(N,N,N‐trimethylammonium)‐hexyl)‐fluoren‐2′‐yl]benzene tetrabromide (1a), 1,4‐bis[9′,9′;9″,9″‐tetra(6″′‐(N,N,N‐trimethylammonium)‐hexyl)‐7′,2″‐bisfluoren‐2′‐yl] benzene octabromide (1b) and 1,4‐bis[9′,9′;9″,9″;9″′,9″′‐hexakis(6″″‐(N,N,N‐trimethylammonium)‐hexyl)‐7′,2″,7″,2″′‐trifluoren‐2′‐yl] benzene dodecabromide (1c). These molecules provide a size‐specific series of water‐soluble oligofluorene molecules with increasing numbers of repeat units to model the interactions between cationic conjugated polymers and DNA. Fluorescence quenching and energy‐transfer measurements were performed with 1a–c and single‐stranded (ss) DNA and double‐stranded (ds) DNA, with and without fluorescein (Fl). These studies show that, on a per‐negative‐charge basis, ssDNA quenches the emission of 1a–c more effectively than dsDNA. Furthermore, we show that the energy‐transfer ratios dsDNA–Fl/ssDNA–Fl are dependent on the number of repeat units in 1a–c.
Organic light‐emitting diodes (LEDs) with small turn‐on voltages are fabricated here using molecules based on the tetrakis(4‐styryldistyrylbenzene)methane framework (see Figure). The synthesis of these molecules is reported, their absorption and luminescence properties are compared, and the effect of device architecture on performance is investigated.
Tetrakis[(4‐(4′‐(2″,5″‐dioctyloxy‐4″‐(4‴‐(2′‴,5′‴‐dioctyloxy‐4′‴‐styryl)styryl)styryl)styryl)styryl)phenyl]methane (T‐6R‐OC8H17) is an organic chromophore that consists of four optoelectronic fragments (“arms”) connected to a tetrahedral point of convergence (carbon). Bulk samples are amorphous as determined by powder diffraction, while differential scanning calorimetry (DSC) is sometimes ambiguous. Film forming properties were studied by atomic force microscopy (AFM) and fluorescence microscopy as a function of casting solvent and heat treatment. The film forming qualities are useful for the fabrication of light‐emitting diodes with low turn‐on voltages. Device performance is also history dependent. The relationship between bulk morphology, film topology, photoluminescence (PL) properties, and light‐emitting diode (LED) performance is discussed. A comparison of these compounds against the parent oligo(phenylenevinylene) arms, with respect to morphology, topology, and PL properties is also presented.
The structure of the CMS inner tracking system has been studied using nuclear interactions of hadrons striking its material. Data from proton-proton collisions at a center-of-mass energy of 13 TeV recorded in 2015 at the LHC are used to reconstruct millions of secondary vertices from these nuclear interactions. Precise positions of the beam pipe and the inner tracking system elements, such as the pixel detector support tube, and barrel pixel detector inner shield and support rails, are determined using these vertices. These measurements are important for detector simulations, detector upgrades, and to identify any changes in the positions of inactive elements.
The CMS tracker consists of 206 m 2 of silicon strip sensors assembled on carbon fibre composite structures and is designed for operation in the temperature range from −25 to +25 • C. The mechanical stability of tracker components during physics operation was monitored with a few µm resolution using a dedicated laser alignment system as well as particle tracks from cosmic rays and hadron-hadron collisions. During the LHC operational period of 2011-2013 at stable temperatures, the components of the tracker were observed to experience relative movements of less than 30 µm. In addition, temperature variations were found to cause displacements of tracker structures of about 2 µm/ • C, which largely revert to their initial positions when the temperature is restored to its original value.
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