Daoben Zhu

Direct observation of C60 LB film with scanning tunneling microscopy

Abstract We report the direct imaging of monolayer LB film of C 60 . The LB film was prepared onto an Au(100) surface by the vertical dipping method for scanning tunneling microscopy (STM) measurements. Ordered arrays of C 60 molecules and close-packed molecular aggregation in the film are shown on the STM images. The calculated diameters along two mutually perpendicular directions in the arrays are 0.635±0.013 and 0.572±0.024 nm, respectively. Our results demonstrate that the molecular shape of C 60 is easily compressed into an ellipsoid while forming the LB film.

An Hg2+-gated chiral molecular switch created by using binaphthalene molecules with two anthracene units and two 1,3-dithiole-2-thione (1,3-dithiole-2-one) units.

By integrating the features of anthracene, 1,3-dithiole-2-thione, and binaphthalene units, (S)-1 and its analogue (S)-2, which contains two 1,3-dithiole-2-one units instead of 1,3-dithiole-2-thione, were studied for creating a new molecular regulation system and building a gated chiral molecular switch. The results show that the photodimerization is controlled by the remote functional-group transformation of C=S into C=O, thus providing an elegant example of molecular regulation. The photodimerization of two anthracene units induces circular dichroism (CD) spectral variation. Overall, the CD spectrum can be remotely modulated by Hg2+ in (S)-1, which leads to an Hg2+-gated chiral molecular switch.

Carrier transport and high-efficiency electroluminescence properties of copolymer thin films

A novel copolymer with moieties capable of charge transport and electroluminescence was synthesized. The drift mobilities of electron and hole in the spin-coated films of the copolymer on silicon substrate have been determined by the time-of-flight technique. The shape of the photo-current curves obtained for the transport of both electron and hole is typical for dispersive transport in organic polymers. Under an electrical field strength of 5:0 £ 10 5 V/cm, the drift mobility of electron and hole is 4:78 £ 10 26 and 3:46 £ 10 26 cm 2 /V s, respectively. A high-efficiency electroluminescent device with the bi-layer structure of ITO/copolymer/2-(4-biphenylyl)-5-(4-tert-butylphenl)-1,3,4,oxadiazole (PBD) /LiF/Al was fabricated. The device emitted a bright blue-green light peaking at wavelength of 496 nm, originating from copolymer with a maximum current efficiency of 10 cd/A and a maximum luminescence efficiency of 2.9 lm/W at the DC drive voltage of 12 V. q 2000 Elsevier Science S.A. All rights reserved.

Langmuir-Blodgett films of fullerene derivatives

Abstract Two C 60 derivatives, dodecylaminofullerene (DAF) and multihydroxydodecylaminofullerene (MHDAF) were prepared. The isotherms showed that the limiting molecular areas of DAF and MHDAF are around 60 A 2 and 64.7 A 2 respectively, which suggests that the aggregations of the molecules at the air-water interface are decreased compared with that of C 60 . The best transfer ratio could be enhanced to 0.7–1 by using the vertical dipping method. The structural characteristics of DAF Langmuir-Blodgett (LB) films were studied by UV-Vis spectroscopy, atomic force microscopy and transmission electron microscopy. The second-order susceptibility χ (2) and molecular hyperpolarizability (β) of 12-layer LB films of DAF are determined to be 3.26 × 10 −6 esu and 1.46 × 10 −28 esu respectively.

Preparation and study on magnetic properties of LB films of 2-(4-(hexadecyloxy) phenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl 3-N-oxide

Abstract The organic molecule with a nitroxyl free radical and hydrophobic alkyl chain, 2-(4-(hexadecyloxy) phenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl 3- N -oxide (HTDIOO), was designed and synthesized. Under suitable conditions, the stable monolayer of this compound formed at the air-water interface could be successfully transferred onto various substrates by the Langmuir-Blodgett (LB) method. The structural characteristics of the LB films were studied by atomic force microscopy, Fourier transform IR spectroscopy, electron spin resonance and small-angle X-ray diffraction techniques. Using magnetic force microscopy, we have observed a quasi-one-dimensional band structure composed of magnetic domains in the local regions of HTDIOO LB films.

Second Harmonic Generation in Langmuir-Blodgett Films of a Novel Phenylhydrazone Dye

Abstract The LB films of a new phenylhydrazone dye, 4-hexadecanoxynaphthyl-4′-nitro phenylhydrazone, were prepared. The second harmonic generation (SHG) from monolayer and multilayers of the dye was measured. The dependence of SHG on number of layers is weaker than the expected square law.