•Graphene oxide has been successfully photoreduced by polyoxometalates.•The influence of the energy level of polyoxometalates on their photoreduction capabilities has been elucidated.•The saturable absorption of the reduced graphene oxide has been studied by Z-scan method.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.Graphical abstract

Graphene oxide (GO) nanosheets and polyoxometalate clusters, H3PW12O40 (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.

A new concept of the efficient fabrication and design of three layer photoresponsive core–shell–corona (CSC) nanostructures by the co-assembly of diblock copolymers with azobenzene-containing homopolymers is presented. Depending on the azobenzene-containing homopolymer content, the formation of CSC vesicles and CSC micelle-like nanostructures are observed, which are characterized by UV–vis absorption spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and dynamic light scattering (DLS). The observed nanostructures confirm the recent computer simulations of Xu et al. (J. Phys. Chem. B, 2010, 114, 1257). All co-assemblies are photoresponsive and show reversible cis–transphotoisomerization. Irradiation of the spherical CSC micelle-like nanostructures by polarized light induces their deformation to ellipsoidal-core-within-ellipsoidal-shell and ellipsoidal-core-within-spherical-shell nanostructures, respectively. The type of photoinduced deformation depends on the initial size of the spherical CSC micelle-like nanostructures. These CSC nanostructures could be used as photo-controlled templates for complex nanostructures.

We have developed a green method to reduce graphene oxide via a UV-irradiated photoreduction process in which H3PW12O40 was used as photocatalyst. Moreover, H3PW12O40 can adsorb on the reduced graphene oxide as anionic stabilizer and lead to water dispersible graphene sheets.

We investigate the effects of solvents on structure, morphology and photophysical properties of micelle-like assemblies of an azo chromophore-functionalized polydiacetylene (polyAzoDA) and polymerized tricosa-10,12-diynoic acid (polyTDA) for comparison. Using mixtures of water with glycol, DMSO, ethanol and THF, we systematically vary the solubility parameters and observe blue-to-red color changes of polydiacetylenes. Teas plots are used to estimate the strength of polymer−solvent interactions and explain the properties of polyAzoDA supramolecular assemblies in different solvent environments. In poor solvents, polyAzoDA forms rod-like micelles and the photoisomerization is strongly hindered by the aggregation of azo chromophores. At increasing content of organic solvents, polyAzoDA becomes gradually swollen, as indicated by the onsets of blue-to-red color changes, starting trans−cis isomerizations of the azo groups, and changes of the structures as seen in SEM images. At large ethanol content, we observe that photoisomerization of azobenzene groups induces a morphological transition and a color change of the polydiacetylene backbone.

We demonstrate a new strategy for improved stabilization of polydiacetylene micelles. They show temperature-induced color changes, which are fully reversible even at varying pH. A novel azo chromophore-functionalized amphiphilic diacetylene molecule is synthesized and used to prepare self-assembled cylindrical micelles. The micelles can be polymerized by 254 nm light irradiation. The azo chromophores form H- and J-like aggregates in the polydiacetylene micelles and increase the stability of the micelles, which leads to fully reversible thermochromism of the micelles in the temperature range between 20 and 90 °C and the pH range between 5.6 and 9.6.

We prepare hydrogen-bonding complexes of the diacetylene derivatives 10,12-tricosadiynoic acid, 4,6-heptadecadiynoic acid, and ((E)-4-((4-(tricosa-10,12- diynoyloxy)phenyl)diazenyl)benzoic acid and poly(4-vinylpyridine) in organic solvents. The complexes are spin-cast and form high-quality thin films, which can be photopolymerized and yield the blue phase of polydiacetylenes. A cross-linked network of the hydrogen-bonding complex is formed and shows improved stability to organic solvents. We demonstrate sensor capabilities for various organic solvents and gases by means of the blue-to-red color changes of polydiacetylenes. Based on the different solubility of the hydrogen-bonding complex before and after UV irradiation, photolithography can be employed to fabricate microstructures for polydiacetylene-based devices.

We studied MEH-PPV and MEH-PPB which are derivatives of poly(p-phenylenevinylene) (PPV), synthesized via the so-called HORNER-polycondensation route. The residual sub-bandgap absorptions of MEH-PPV were found to be extremely low at λ⩾1064 nm as compared to other PPVs. We attribute this fact to its very low defect density. MEH-PPV enables the fabrication of slab waveguides with propagation losses which are well below 1 dB/cm at 1064 nm. Comparative studies of the cubic nonlinearity χ(3), the photodegradation and the damage thresholds at 1064 nm of PPV, MEH-PPV and MEH-PPB demonstrate that polycondensation-type MEH-PPV has the greatest potential for the realization of nonlinear optical waveguide applications.

We have developed a green method to reduce graphene oxide via a UV-irradiated photoreduction process in which H3PW12O40 was used as photocatalyst. Moreover, H3PW12O40 can adsorb on the reduced graphene oxide as anionic stabilizer and lead to water dispersible graphene sheets.