New P‐type of poly(4‐methoxy‐triphenylamine)s derived by coupling reactions: Synthesis,electrochromic behaviors,and hole mobility

Methoxy‐substituted poly(triphenylamine)s, poly‐4‐methoxytriphenylamine ( PMOTPA ), and poly‐N,N‐bis(4‐methoxyphenyl)‐N′,N′‐diphenyl‐p‐phenylenediamine ( PMOPD ), were synthesized from the nickel‐catalyzed Yamamoto and oxidative coupling reaction with FeCl₃. All synthesized polymers could be well characterized by ¹H and ¹³C NMR spectroscopy. These polymers possess good solubility in common organic solvent, thermal stability with relatively high glass‐transition temperatures (T_gs) in the range of 152–273 °C, 10% weight‐loss temperature in excess of 480 °C, and char yield at 800 °C higher than 79% under a nitrogen atmosphere. They were amorphous and showed bluish green light (430–487 nm) fluorescence with quantum efficiency up to 45–62% in NMP solution. The hole‐transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. All polymers exhibited reversible oxidation redox peaks and E_onset around 0.44–0.69 V versus Ag/AgCl and electrochromic characteristics with a color change under various applied potentials. The series of PMOTPA and PMOPD also showed p‐type characteristics, and the estimated hole mobility of O ‐ PMOTPA and Y ‐ PMOPD were up to 1.5 × 10^?4 and 5.6 × 10^?5 cm² V^?1 s^?1, respectively. The FET results indicate that the molecular weight, annealing temperature, and polymer structure could crucially affect the charge transporting ability. This study suggests that triphenylamine‐containing conjugated polymer is a multifunctional material for various optoelectronic device applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4037–4050, 2009     

Unusual decrease in conductivity upon hydration in acceptor doped, microcrystalline ceria

The impact of hydration on the transport properties of microcrystalline Sm(0.15)Ce(0.85)O(1.925) has been examined. Dense, polycrystalline samples were obtained by conventional ceramic processing and the grain boundary regions were found, by high resolution transmission electron microscopy, to be free of impurity phases. Impedance spectroscopy measurements were performed over the temperature range 250 to 650 °C under dry, H(2)O-saturated, and D(2)O-saturated synthetic air; and over the temperature range 575 to 650 °C under H(2)-H(2)O atmospheres. Under oxidizing conditions humidification by either H(2)O or D(2)O caused a substantial increase in the grain boundary resistivity, while leaving the bulk (or grain interior) properties unchanged. This unusual behavior, which was found to be both reversible and reproducible, is interpreted in terms of the space-charge model, which adequately explains all the features of the measured data. It is found that the space-charge potential increases by 5-7 mV under humidification, in turn, exacerbating oxygen vacancy depletion in the space-charge regions and leading to the observed reduction in grain boundary conductivity. It is proposed that the heightened space-charge potential reflects a change in the relative energetics of vacancy creation in the bulk and at the grain boundary interfaces as a result of water uptake into the grain boundary core. Negligible bulk water uptake is detected under both oxidizing and reducing conditions.     

Multilevel Nonvolatile Flexible Organic Field‐Effect Transistor Memories Employing Polyimide Electrets with Different Charge‐Transfer Effects

The electrical memory characteristics of the n‐channel organic field‐effect transistors (OFETs) employing diverse polyimide (PI) electrets are reported. The synthesized PIs comprise identical electron donor and three different building blocks with gradually increasing electron‐accepting ability. The distinct charge‐transfer capabilities of these PIs result in varied type of memory behaviors from the write‐one‐read‐many (WORM) to flash type. Finally, a prominent flexible WORM‐type transistor memory is demonstrated and shows not only promising write‐many‐read‐many (WMRM) multilevel data storage but also excellent mechanical and retention stability.

     

A manganese-ferritin nanocomposite as an ultrasensitive T2 contrast agent

T(2) contrast is gaining importance in high field strength MRI. We report a strategy for developing a T(2) contrast agent from paramagnetic metal ions synthesized within an engineered protein cage. The manganese-ferritin nanocomposite showed high T(2) relaxivity indicating its potential as an ultrasensitive T(2) contrast agent.     

Arrays of horizontally-oriented mini-reservoirs generate steady microfluidic flows for continuous perfusion cell culture and gradient generation

This paper describes the use of arrays of horizontally-oriented reservoirs to deliver liquids through microchannels at a constant flow rate over extended periods of time (hours to days). The horizontal orientation maintains a constant hydraulic pressure drop across microfluidic channels even as the volumes of liquids within the reservoirs change over time. For a given channel-reservoir system, the magnitude of the flow velocity depends linearly on the height difference between reservoirs. The simple structure and operation mechanism make this pumping system versatile. A one-inlet-one-outlet system was used to continuously deliver media for perfusion cell culture, and an array of inlet reservoirs coupled to an outlet reservoir via microchannels was used to drive flows of multiple laminar streams. The parallel pumping scheme conveniently generated various smooth and step concentration gradients, and allowed evaluation of the effect of colchicine on myoblasts. Since the reservoir arrays are configured to be compatible with commercialized multichannel pipettors designed for 96 well plate handling, this simple pumping scheme is envisioned to be broadly useful for medium to high throughput microfluidic perfusion cell culture assays, cell migration assays, multiple laminar flow drug tests, and any other applications needing multiple microfluidic streams.     

Syntheses,properties, and field‐effect transistors of small band gap quinoxaline‐ and thienopyrazine‐vinylene/ethynylene conjugated polymers

New conjugated copolymers of quinoxaline (AQ) and thienopyrazine (ATP) with vinylene (V) or ethynylene (E), poly[2,3‐bis(4‐(2‐ethylhexyloxy)phenyl)‐quinoxaline vinylene] (PAQV), poly[2,3‐bis(4‐(2‐ethylhexyloxy)phenyl)‐quinoxaline ethynylene)] (PAQE), poly[2,3‐bis(4‐(2‐ethylhexyloxy)phenyl)‐thieno[3,4‐b]pyrazine vinylene] (PATPV), and poly[2,3‐bis(4‐(2‐ethylhexyloxy)phenyl)‐thieno[3,4‐b]pyrazine ethynylene] (PATPE), were successfully synthesized by Stille coupling reaction. The optical band gaps of the PAQV, PAQE, PATPV, and PATPE were 1.86, 2.00, 0.88, and 0.90 eV, respectively, whereas the electrochemical band gaps were 1.99, 2.06, 1.00, and 1.06 eV, respectively. The reduced steric hindrance by the incorporation of the V or E linkage or the intramolecular charge transfer between the acceptor and the V or E linkage led to the small band gap. The AQ/ATP‐vinylene copolymers exhibited much higher vis/near infrared absorption intensity than the AQ/ATP‐ethynylene suggested the stronger π–π* transition intensity in the former and led to better charge‐transporting characteristics. The saturation field‐effect hole mobilities of the PATPV were 2.1 × 10^?3, 1.7 × 10^?2, and 1.1 × 10^?2 cm² V^?1 s^?1 on bare, octyltrichlorosilane (OTS)‐treated, and octadecyltrichlorosilane(ODTS)‐treated SiO₂, respectively, with on‐off current ratios of 35, 6.02 × 10², and 7.56 × 10². On the other hand, the estimated field‐effect transistor hole mobility of the PATPE was in the range of 1.7 × 10^?6–8.1 × 10^?4 cm² V^?1 s^?1, which was significantly smaller than those of the PATPV. The small band gaps and high charge carrier mobility of the prepared copolymers suggested their potential applications for near‐infrared electronic and optoelectronic devices. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 74–81, 2010