Suizhou Yang

PHOTOINDUCED SURFACE RELIEF GRATINGS ON AZOCELLULOSE FILMS

Surface relief gratings (SRG) on films of azobenzene–modified cellulose (azocellulose) with ultrahigh molecular weight were holographically recorded in a single step. Surface modulation depth of the SRGs increased with the degree of substitution (DS) of the azobenzene chromophores in the cellulose as well as with the grating spacing. Large surface modulations over 500 nm on all samples were obtained with a grating spacing of 4 μm. A linear increase of photoinduced birefringence with the azobenzene chromophore concentration in these photodynamic polymers was also observed. The maximum birefringence of 0.11 was achieved for an azocellulose polymer with a DS of 0.99. †Deceased.

BIOLOGICALLY DERIVED PHOTOACTIVE MACROMOLECULAR AZODYES

Azophenols with various substituents at the para position of the phenyl ring were enzymatically polymerized in the presence of H2O2. Structural characterization of the synthesized polymers by FTIR, FT-Raman, and NMR (1H and 13C) spectroscopy confirms our previous observation that this enzymatically catalyzed coupling reaction occurs primarily at the ortho positions, with some substitution at the meta position of the phenol ring. The strong constraint and poor packing of the azobenzene chromophores in the polymer leads to a significant blue shift of the π-π* transition absorption and slow photoisomerization and thermal relaxation in comparison to the monomers. Surface relief gratings (SRG) with large surface modulation have been fabricated on these enzymatically synthesized polymer films. †Deceased.

Enhancing the inscription rate of surface relief gratings with an incoherent assisting light beam

A beam of light that is incoherent to the recording beams and has its polarization orthogonal to the recording beams is shown to assist the recording process of azo-functionalized polymers through the enhancement of trans–cis–trans cycling. Recording with s:s polarization has earlier been shown to result in very small surface modulations. However, with the help of an incoherent assisting beam, it can record a large surface modulation with a diffraction efficiency of 20.7%. The incoherent assisting beam also leads to an acceleration of the grating formation rate for the recording beams with p:p and 45°:45° polarization.

Synthesis and Characterization of Fluorescent Cellulose

Abstract A new cellulose based fluorescent polymer has been successfully synthesized by esterificaction of 1‐pyrenebutyric acid and cellulose. This polymer was characterized by solid state 13C cross‐polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), ultra‐violet‐visible (UV‐VIS) and fluorescence spectroscopic techniques. Spectroscopic results show that the pyrene chromophores have been covalently linked to cellulose. The quenching of fluorescence of by dinitrotoluene (DNT) follows the Stern–Volmer relationship. This suggests the potential use of this polymer in sensor and other applications. #Dedicated to the memory of Professor Sukant K. Tripathy.

RAMAN MICROSCOPY AND MAPPING OF SURFACE-RELIEF GRATINGS RECORDED ON AZOCELLULOSE FILMS

Raman spectra and mapping of surface-relief grating (SRG) recorded on a solution cast azocellulose film are reported. The Raman spectra clearly show that the chromophores adopt the trans conformation. Within the detection limit of the measuring system the chromophores appear to be randomly oriented on the crest and in the valley of each groove in the grating, as a result of relaxation following the inscription procedure of the SRG. The presence of the SRG was detected as a variation of the peak intensity, which is in agreement with the surface modulation of the grating morphology. †Deceased.

Patterning Flexible Substrates Using Surface Relief Structures in Azobenzene Functionalized Polymer Films

A novel method for maskless micro-patterning of polymeric substrates is presented. First, an azobenzene functionalized polymer film is spin-coated on a Poly (ethylene terephthalate) (PET) sheet. Then surface relief structures are optically inscribed on the polymer film by interference of laser beams. The patterned azobenzene functionalized film is then etched in the plasma chamber such that the gratings are transferred to the PET substrate. Finally, any remaining azobenzene functionalized polymer is dissolved away using an appropriate solvent. This method of patterning can be broadly applied to a variety of flexible/polymeric substrates and the resolution is not limited by the substrate thermo-mechanical properties.

Conformation of azobenzene-modified poly(α-L-glutamate) (AZOPLGA) in thin films : Solid state NMR studies

Abstract The conformations of azobenzene‐modified poly(α‐L‐glutamate)s (AZOPLGA) with a different degree of functionalization were examined by solid state 13C NMR. The polymer main chain conformations in AZOPLGA powders (precipitated from reaction system) changes from α‐helix to β‐sheet when the degree of functionalization increases from 12% to 56%. In addition, the solvent used for fabricating films plays an important role in organizing AZOPLGA backbones into characteristic conformation. For AZOPLGA56 (AZOPLGA with 56% of functionalization) cast films, the polymer backbones can assume conformations ranging from order state (β‐sheet) to random coil by changing the solvent for fabrication. In contrast, the effect of solvent on the conformation of AZOPLGA23 (AZOPLGA with 23% of functionalization) is not so significant. When compared with AZOPLGA23 powder (precipitated from reaction system), the helical conformation increases for AZOPLGA23 film cast from TFA. However, the fractions of α‐helix and β‐sheet conformation in AZOPLGA23 films (cast from DMF or pyridine) are nearly identical to that of AZOPLGA23 power. Moreover, even though the polymer backbones are random coil in AZOPLGA56 films when cast from TFA, some locally ordered domain can be observed. Lastly, the effect of the azo content appears to play a dominant role over the effect of solvents in directing the conformation of these polymers. #Dedicated to the Memory of Professor Sukant K. Tripathy.

Enzymatically synthesized electronic and photonic polymers

Macromolecular dyes such as polyazophenols and polypyrene derivatives have been enzymatically synthesized. These macrodyes show interesting optical and electronil properties. Fluorescence and optical recording properties of these novel polymers have been investigated.