Isomerization-induced surface relief gratings formation: A comparison between the probe and the matrix dynamics

We report molecular dynamics simulations of the effect of the photoisomerization of probe molecules on the nonequilibrium dynamics of a bulk amorphous matrix. Is it the matrix or the probe that drives the dynamics in SRG formation? In the first picture, the probe isomerization induces the motion of the probe inside the matrix. The motion of the probe then induces molecular motions inside the matrix. In the second picture, the probe isomerization induces a modification of the matrix diffusion mechanism. The diffusion of the matrix then induces the motion of the embedded probe. To answer this question, we compare the motion of the probe molecules and the motion of the matrix molecules in various thermodynamic conditions. We show that when the isomerization is switched on, the matrix molecules surrounding the probe move faster than the probe. Around the probe, the structural relaxation time of the matrix molecules is shorter than the probe relaxation time and the diffusion of the matrix molecules is larger than the probe diffusion. These results show that the matrix motions drive the dynamics

Simulation of isomerization-induced motions in a blend of different PMMA melts doped with DR1 chromophores

Date du colloque&nbsp;: 01/2010</p

Mastering Nano-Objects with Photoswitchable Molecules for Nanotechnology Applications

Advance in the fabrication of nano-objects becomes more important for the development of new nanodevices with local properties leading to new functional devices. In this direction, the assembly of nanometer-scaled building objects into device configurations and functionalization is a promising investigated research field in nanotechnology. Optical recording and photofabrication techniques that exploit changes in material properties have gained importance, and there is a requirement for a decrease of the dimensions of the recording and processing surfaces. Photochromic materials leading to submicron structures responding to stimuli and in particular light are the best materials that exhibit multifunctional behaviors. Photomechanical properties of azopolymers show the perfect performance in photoinduced nanopatterning and reshaping by tailored light fields. Azopolymer nanostructures are then recognized as an excellent choice for a broad range of fundamental and applied research in modern nanotechnology. This chapter shows how polymer nanofilms, nanotubes, nanospheres, or nanowires containing azobenzene can be controlled by light for new photonics applications. Spatially confined excitation of unidirectional motions could make possible the local control of mechanical properties of the material and its structuration. The unprecedented flexibility of the reported photofluidization lithography with this material allows producing well-defined structures as lines, ellipsoids, rectangles, and circles at azopolymer surface with several tenth nanometers structural features

New cyclopropano 70 fullerene derivatives for the photovoltaic application

New cyclopropano 70 fullerenes derivatives were synthesised for photovoltaic (PV) application. The organic PV cells realized with these molecules blended with RR-P3HT polymer provided improved characteristics: 1.5% conversion efficiency (eta%), 9.29 mA/cm2 current density, 0.51 V open circuit voltage and 0.34 fill factor. The IPCE spectrum for P3HT: cyclopropano 70 fullerene cells shows a new peak around 430 nm with 71% external quantum efficiency. This explains the increased current density

Cognitive ability process at the molecular level

In the standard SRG formation in azo-dye containing photoactive polymers, the photoactive molecules are excited by a coherent illumination pattern. The highly reactive molecules move in a non-uniform way, inducing a mass transport from the bright regions to the neighbouring dark regions. The maximum heights of the light induced SRG correspond to light intensity minima. We show that a well-defined surface relief grating is induced in an azo-polymer film by the combination of one low power coherent laser beam with another high power incoherent and unpolarised beam. The information brought by the coherent signal beam has been transmitted to peripheral incoherent regions by the molecular self-assembling process: i.e., the organised molecules communicate non-local information about photo-induced structural organisation to the non organised neighbouring ones. They communicate by exchanging light through surface relief variations. In this way, we see that a totally incoherent beam can provide the movement which is necessary to induce a well-defined SRG. We find in this way one of the simplest systems allowing to figure out the minimal requirements to organise disordered materials into well organised structures. We verify experimentally that random motion plus information exchange lead to self-organisation. Our experiment shows that complex behaviour can be experimented using simple systems: weak coherent light can serve as a seed to create information into a polymer film in such a way that molecules powered by incoherent light will build and transmit well defined complex structures

Two-Photon absorption cross-section measurement by thermal lens and nonlinear transmission methods in organic materials at 532 nm and 1064 nm laser excitations

Experimental results concerning two-photon absorption (TPA) cross-section measurement using nonlinear transmission (NLT) method and a new pump-probe mode-mismatched thermal lens (TL) scheme, in picosecond regime are reported. Both methods are used in a prospect of comparison. Values of the TPA coefficient and cross-section in three common solvents (Chloroform, Benzene and Nitrobenzene) and new synthesized perylenediimide derivatives (PDI) at 532nm and 1064nm wavelengths are given

Self-reconstructing all-optical poling in polymer fibers

Self-sustained all-optical poling second-harmonic generation (SHG) experiments are conducted in single-core and multicore dye-doped poly(methyl methacrylate) optical fibers. By tuning the polarization of the fundamental beam, the SHG signal is degraded and is reconstructed spontaneously up to its initial level. We found a new situation in which the photo-induced self-organization of azo polymers creates a well-ordered periodic structure