We report the nonvolatile memory characteristics of pentacene-based organic field-effect transistors (OFET) using polystyrene para-substituted with p-conjugated oligofluorenes (P(St-Fl) n (n ¼ 1-3)) as chargeable polymer electrets. Effects of fluorene conjugated length on the surface structure and memory characteristics of pentacene OFET were investigated. Among these polymer electrets, the device with the P(St-Fl) exhibited the highest field-effect mobility of 0.47 cm 2 V À1 s À1 due to the largest grain size of pentacene growth. The device with P(St-Fl) 3 revealed the largest hysteresis window of 76 V due to it having the longest fluorene conjugation length among the studied electrets. The smallest difference of the HOMO energy level between pentacene and P(St-Fl) 3 facilitated the charge transfer from pentacene to the polymer electret. The shifts on the transfer curves in both positive and negative directions could be reversibly controlled when applied an external gate bias of AE100 V for a short time (1 ms), indicating the fast trapping-detrapping ability of the polymer electrets. The devices showed excellent nonvolatile behaviors for bistable switching. The ON and OFF states were maintained over 10 4 s with the I on /I off current ratio of 10 5 -10 6 . The write-read-erase-read (WRER) cycles could be operated over 100 cycles. This study suggested that surface characteristics, charge transport, and memory characteristics of pentacene-based OFET can be manipulated by polymer electrets with different pendent conjugation length.

We report novel thermoresponsive electrospun (ES) fibers prepared from multifunctional random copolymers of poly((2-(dimethylamino)ethyl methacrylate)-co-(stearyl acrylate) -co-(9,9-dihexyl-2-(4-vinylpenyl)-9H-fluorene)) (poly(DMAEMA-co-SA-co-StFl)). The moieties of DMAEMA, SA, and StFl were designed to exhibit the thermoresponsive, physical cross-linking, and fluorescent functionality, respectively. The effects of the copolymer compositions on the morphology and photoluminescence of the prepared ES fibers were explored. The prepared P4 copolymer with the DMAEMA/SA/StFl mole ratio of 92/3/5 showed the lower critical solution temperature (LCST) of 32.5 °C. A significant temperature-dependent swelling and de-swelling behavior was found in the P4 ES fibers, which had the diameter of 753 ± 174 nm and 5-10 nm StFl aggregated domain. Accompanied with volume-changing on the P4 ES fibers, a reversible photoluminescence (PL) quenching was also observed during the heating and cooling cycle between 40 and 60 °C. Such reversible switching of the "on-off" PL intensity was probably due to the light absorption ability of the StFl moiety, resulted from the extended/compact structural transformation on the PDMAEMA moiety. Furthermore, the high surface/volume ratio of the ES fibers led a much better temperature response compared with the corresponding spin-coated film. The present study demonstrated that the ES fibers prepared from multifunctional copolymers exhibited the thermoreversible variation on both volume and photoluminescence intensity.

Epidermal growth factor receptor (EGFR)-mediated cell signaling is critical for mammary epithelial cell growth and survival; however, targeting EGFR has shown no or only minimal therapeutic benefit in patients with breast cancer. Here, we report a novel regulatory mechanism of EGFR signaling that may explain the low response rates. We found that breast tumor kinase (Brk)/protein-tyrosine kinase 6 (PTK6), a nonreceptor protein tyrosine kinase highly expressed in most human breast tumors, interacted with EGFR and sustained ligand-induced EGFR signaling. We demonstrate that Brk inhibits ligand-induced EGFR degradation through uncoupling activated EGFR from Cbl-mediated EGFR ubiquitination. In addition, upon activation by EGFR, Brk directly phosphorylated Y845 in the EGFR kinase domain, thereby further potentiating EGFR kinase activity. Experimental elevation of Brk conferred resistance of breast cancer cells to cetuximab (an EGFR-blocking antibody)-induced inhibition of cell signaling and proliferation, whereas knockdown of Brk sensitized the cells to cetuximab by inducing apoptosis. Our findings reveal a previously unknown role of Brk in EGFR-targeted therapy.

We report bistable non-volatile memory devices based on polystyrene derivatives containing pendent electron-donating mono-, di-, and tri(9,9-dihexylfluorene), which are denoted as poly(St-Fl), poly(St-Fl(2)), and poly(St-Fl(3)), respectively. The effects of the oligofluorene chain lengths and polymer surface structures on the memory characteristics were explored. Poly(St-Fl)-, poly(St-Fl(2))-, and poly(St-Fl(3))-based devices exhibited a flash memory characteristic with different turn-on threshold voltages of 2.8, 2.0, and 1.8 V, respectively, which was on the reverse trend with the highest occupied molecular orbital levels of -5.86, -5.80, and -5.77 eV. Moreover, the memory device showed a high ON/OFF current ratio of 2.5 x 10(4) and a long retention time of 10(4) s. The possible mechanism of the switching behavior was explained by the space-charge-limited-current theory and filamentary conduction. The larger aggregation domain size of the polymer thin film processed from the mixed solvent of chlorobenzene/N,N-dimethylformamide probably promoted the diffusion of the Al atoms into the polymer film and formed the conduction channel. Thus, it significantly reduced the turn-on threshold voltage on the studied polymer memory devices. The present study suggested that the polymer memory characteristics could be efficiently tuned through the pendent conjugated chain length and surface structures.