Shen Yuquan

Photoisomerization of sterically hindered azobenzenes

Abstract The photoisomerization yields of a homologous series of o , o , o ′, o ′-substituted azobenzenes have been determined by excitation of the low lying 1 (n,π*) and the higher lying 1 (π,π*) states. For more severe steric hindrance, i.e. with substituents more bulky than methyl, the E → Z quantum yields are independent of the excitation wavelength, which is in contrast with those for unsubstituted azobenzene, and they seem to decrease with increasing volume of the substituents. This provides further support for our hypothesis of photoisomerization of normal azo compounds: inversion in the lowest states and rotation in the higher states.

The second-order nonlinear optical properties of a series of polyesters containing push-pull azobenzene chromophore in their side chain

The second harmonic coefficient d33 values of a series of polyester nonlinear optical (NLO) polymers, differing in their electron withdrawing substituent, were experimentally measured. The observed order of contribution of the substituents towards d33 value was rationalized by a frequency factor dependence. Excellent photostability and the highest d33 value among the series have been found for the polyester with 2,4-dinitro substituents in the side chain. A possible influence of intermolecular interaction is also indicated.

The synthesis of highly active thiophene ring-containing chromophore components for photonic polymers based on a newly designed route

2-Aminothiophene derivatives are the key intermediates for the present synthesis. It is known that the synthesis of 2-aminothiophene is troublesome although it is a rather simple heterocycle. In this work, an early report was newly developed as a basis for the efficient synthesis of thiophene-ring-containing chromophore components for photonic polymers. 2-Amino-5-nitrothiophene and 2-amino-3,5-dinitrothiophene were synthesized in excellent yield. After diazotization, the 2-aminothiophene derivatives were directly treated with N-phenyldiethanolamine to afford two-electron push–pull compounds. A similar styryl compound was also prepared. All of these chromophore molecules have further polymerizable hydroxy groups on one end of the molecule. These compounds are currently showing interesting potential in making highly sensitive, nonlinear optical polymeric materials.

Observation of Optical Bistabilities in a Doped Polymer Thin Film Quasi-waveguide

Optical bistability was observed and studied in the output of reflected beam as well as in that of m-lines in a doped polymer thin film quasi-waveguide. The physical origin was demonstrated to be the existence of a mode spectrum and the high third-order nonlinearity of the polymer film. It was also observed for the first time that the intensity variation of the reflected beam and the m-line in the hysteresis loops are complementary to each other.

Observation of Optical Bistability Hysteresis Loop with Surface Waves in Doped Polymer Film

Optical bistability hysteresis loop has been observed experimentally with a setup using prism excitation of surface wave in a doped polymer thin film. A simple model has been developed to analyze its operation. The observed bistability hysteresis loop can be explained in terms of surface plasmon excitation and laser induced refractive index variations.

Synthesis and characterization of an active styrlthiophene monomer and its polyurethane with second-order optical nonlinearity

A novel monomer, (trans)-7-[4-N,N-(di-β-hydroxyethyl) amino-benzene]-ethenyl-3,5- dinitrothiophene (HBDT), and the corresponding prepolymer, polyurethane were synthesized and characterized. The details of synthesis of the monomer and its further polymerization were presented. The prepolymer and polyurethane exhibited good thermal stability and good solubility in common organic solvents. The d33 coefficient of the poled films was determined to be 40.3 pm/V.

Ultrafast Time-Resolved Optical Kerr Effect in Phthalocyanine Langmuir-Blodegett Film

The resonant optical Kerr effect in the Langmuir-Blodegett film of 2, 9, 16, 23-tetraheptadecylamido substituted vanadyl phthalocyanine was measured with femtosecond laser pulses to determine the relaxation time, and meanwhile slow decay components were observed. The ultrafast nonlinearity of the molecule was also measured.

AN EASY APPROACH FOR ESTIMATING ABSORPTION LOSS IN ORGANIC THIN SOLID FILMS

An UV-VIS-Near-IR spectroscopic method for determination of optical loss in organic/polymeric films has been suggested. The optical losses of two polyimide polymers with push-pull azobenzene chromophore attached were examined by this method and the data were calibrated by conventional optical method.

PHOTO-INDUCED ENHANCEMENT OF THE THIRD-ORDER OPTICAL NONLINEARITY IN AZOBENZENE COMPOUND ON THE PICOSECOND TIME SCALE

Photo-induced enhancement processes of the third-order optical nonlinearity were observed in azobenzene solution under a 30ps pulse pumping at 532 nm. Weinvestigated the time evolution of the enhancement and found that it was mainly due to the population of the first excited state. By theoretical simulation of the enhancement processes, the values of the hyperpolarizabilities of the sample-molecules at ground state and at excited state, γg and γs1, were determined to be 1.11 × 10-33 esu and 7.40 × 10-33 esu, respectively.

Ultrafast Optical Response of Phthalocyanine Langmuir-Blodegett Film

The mechanism of 2, 9, 16, 23- tetra-heptadecylamido substituted vanadyl phthalocyanine Langmuir-Blodegett film was studied with femtosecond laser pulses. An ultrafast decay due to phonon-exciton coupling greatly affected by temperature, and exciton-exciton annihilation leading to the recovery of the ground state (T similar 10 ps) and an even slower relaxation were observed.