Azobenzene

A new type of photo-responsive perylene diimide–azobenzene dyad (PDI–AZO) was synthesized by covalently adjoining azobenzene chromophore to N-imide position of perylene diimide. The optical properties, photoisomerization and self-assembly morphology of the resultant composites were characterized by UV–vis absorption, photoluminescence (PL) spectra and scanning electron microscope. Larger one-dimension nanobelts were observed in self-assembly PDI–AZO due to the strong molecule stacking. The red-shifted bands arise from the larger conjugation extension by p-electron overlap of perylene ring and azobenzene chromophore. The spectral changes upon the irradiation of ultraviolet light show that larger conjugation extension does not significantly affect the photochromism rate, but it retards the further photoisomerization of azobenzene units in PDI–AZO. The PL quenching of PDI–AZO is dominated by the transfer of the excitons before reverting to the ground state accompanied by the radiation due to the larger conjugation extension.  2007 Elsevier B.V. All rights reserved.

Perylene-sensitized multi-walled carbon nanotubes (PV-MWNT) have been prepared by a π-stacking between nanotubes and perylene derivatives, N,N'-diphenyl glyoxaline-3,4,9,10-perylene tetracarboxylic acid diacidamide (PV). The resultant nanocomposites have been characterized by transmission electron microscope (TEM), UV–vis absorption, photoluminescence (PL) and photocurrent spectra. Long range ordering can be observed in the form of PV-MWNT via π-stacking by TEM. Red-shift in the optical spectra consisting of the UV–vis absorption and PL spectra with the attraction of PV on the surface of the MWNTs were observed. The evident quenching in PL spectra of PV-MWNT was ascribed to the absorption and transfer of recombination energy by MWNT. Photosensitivity spectra demonstrated an increasing photocurrent in the ultraviolet region and a broadening photosensitivity in the red spectral region for solar cells based on PV-MWNT.

Composite film containing titania electrostatically linked to oxidized multiwalled carbon nanotubes (TiO2-s-MWNTs) was prepared from a suspension of TiO2 nanoparticles in soluble carbon nanotubes. The structure of the film was analysed principally by Fourier transform infrared spectroscopy, scanning electron micrography and x-ray diffraction. The optical and electrical characterizations of the film were investigated by UV–vis spectrum, photoluminescence and photoconductivity. The enhancement of photocurrent in the TiO2-s-MWNT film is discussed by taking the photoinduced charge transfer between the MWNT and TiO2 into consideration.

Poly(3,4-ethylenedioxythiophene) (PEDOT) nanorods (80–150 nm in diameter) and nanospheres were synthesized through a self-assembly method using ferric chloride (FeCl3) and ammonium persulfate (APS) as oxidants, respectively, and camphorsulfonic acid (CSA) as the dopant. The PEDOT nanorods showed broader absorption bands, higher crystallinity and much higher room-temperature conductivity (approximately 300 S cm−1) than the PEDOT nanospheres. Such obviously distinct properties of these products were considered to be due to the much lower rate of polymerization with FeCl3 than APS, which made the growth of PEDOT according to the suggested cylinder micelles more moderate and regular; as a result, the morphology of the microstructure changed and the crystallinity, the doping level, the molecular orderliness and the conductivity of PEDOT synthesized under lower rate of polymerization improved intensely at the same time.