Reversible activation of pH-sensitive cell penetrating peptides attached to gold surfaces.

pH-sensitive viral fusion protein mimics are widely touted as a promising route towards site-specific delivery of therapeutic compounds across lipid membranes. Here, we demonstrate that a fusion protein mimic, designed to achieve a reversible, pH-driven helix-coil transition mechanism, retains its functionality when covalently bound to a surface.

Photoreduction of graphene oxide with polyoxometalate clusters and its enhanced saturable absorption.

We investigated the photocatalytic abilities of three Keggin-type polyoxometalate (POM) clusters, H3PW12O40 (PW), H4SiW12O40 (SiW), and H3PMo12O40 (PMo) to reduce graphene oxide (GO) under UV-irradiation in water. UV-vis absorption and X-ray photoelectron spectroscopy were performed and show that PW and SiW can photoreduce GO effectively, in contrast to PMo. We conclude that the LUMO levels of POMs should be located energetically above the work function of GO to enable electron transfer from POM to GO. We also investigated the saturable absorption of GO and reduced GO by means of z-scan experiments at 532 nm. The POM-assisted photoreduction of GO can greatly enhance the saturable absorber properties of GO, which appears useful for modelocking in ultrafast laser systems.

Layer-by-layer assembly and UV photoreduction of graphene-polyoxometalate composite films for electronics.

Graphene oxide (GO) nanosheets and polyoxometalate clusters, H(3)PW(12)O(40) (PW), were co-assembled into multilayer films via electrostatic layer-by-layer assembly. Under UV irradiation, a photoreduction reaction took place in the films which converted GO to reduced GO (rGO) due to the photocatalytic activity of PW clusters. By this means, uniform and large-area composite films based on rGO were fabricated with precisely controlled thickness on various substrates such as quartz, silicon, and plastic supports. We further fabricated field effect transistors based on the composite films, which exhibited typical ambipolar features and good transport properties for both holes and electrons. The on/off ratios and the charge carrier mobilities of the transistors depend on the number of deposited layers and can be controlled easily. Furthermore, we used photomasks to produce conductive patterns of rGO domains on the films, which served as efficient microelectrodes for photodetector devices.

Polyoxometalate assisted photoreduction of graphene oxide and its nanocomposite formation.

We have developed a green method to reduce graphene oxide via a UV-irradiated photoreduction process in which H(3)PW(12)O(40) was used as photocatalyst. Moreover, H(3)PW(12)O(40) can adsorb on the reduced graphene oxide as anionic stabilizer and lead to water dispersible graphene sheets.

Molecular weight effects in the third-harmonic generation spectroscopy of thin films of the conjugated polymer MEH-PPV.

Thin spin-cast films of poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) were prepared from samples whose weight-average molecular weight (Mw) was varied in the range of 10-1600 kg/mol. We have characterized the films by means of transmission and reflection ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy to derive the linear optical constants, and third-harmonic generation spectroscopy with variable laser wavelengths to get the modulus and phase angles of the complex third-order nonlinear optical susceptibility chi(3). Increasing molecular weight yields films with significantly larger chi(3) values, absorption coefficients, and refractive indices. The chi(3) values of films from the largest and lowest Mw differ by a factor of 4, which is caused by chain orientation effects, local field effects, and changes of the effective conjugation length.

Effect of donor-acceptor substitution on the nonlinear optical properties of oligo(1,4-phenyleneethynylene)s studied by third harmonic generation spectroscopy.

Third-harmonic generation (THG) spectroscopy was performed for oligo(1,4-phenyleneethynylene)s (OPEs) with terminal donor-acceptor (DA) substitution and compared to the results of merely donor substituted OPEs and regular OPE chains with 2,5-dipropoxy benzene rings. Both, extension of the conjugation and push-pull effect enhance the molecular hyperpolarizability gamma, even for the DAOPEs, which exhibit a hypsochromic shift of the long-wavelength absorption for increasing length L of the conjugated chain.