Meigong Fan

Polarization patterns hide and display using photoinduced anisotropy of photochromic fulgide

Photoinduced anisotropy of a photochromic pyrrylfulgide/PMMA film was investigated by using two linearly polarized beams. Excitation by linearly polarized light induces into the film an optical axis that has the same polarization as the excitation beam. This causes a change of the transmittance and of the polarization state of the detection beam. With a microscope a matrix of 4x4 light spots with different polarizations were recorded in the pyrrylfulgide/PMMA film. If readout with non-polarized light, the matrix of light spots show no information pattern. However, when readout with differently polarized lights, different patterns can be displayed. The experiment demonstrates that pyrrylfulgide/PMMA films can be used to hide two differently polarized patterns, which may be applied in camouflage technology.

Optical image processing using the photoinduced anisotropy of pyrrylfulgide

A synthesized photochromic compound-pyrrylfulgide--is prepared as a thin film doped in a polymethylmethacrylate (PMMA) matrix. Under irradiation by UV light, the film converts from the bleached state into a colored state that has a maximum absorption at 635 nm and is thermally stable at room temperature. When the colored state is irradiated by a linearly polarized 650 nm laser, the film returns to the bleached state; photoinduced anisotropy is produced during this process. Application of optical image processing methods using the photoinduced anisotropy of the pyrrylfulgide/PMMA film is described. Examples in non-Fourier optical image processing, such as contrast reversal and image subtraction and summation, as well as in Fourier optical image processing, such as low-pass filtering and edge enhancement, are presented.

Optical Properties and Applications of Photochromic Fulgides

ABSTRACT The optical properties and potential applications of four kinds of fulgide and fulgimide were studied. A parallel optical storage apparatus was set up, which could reach the area density of 4.8 × 107 bits/cm2 on the fulgide/PMMA film. Fourier transform orthogonal circular polarization holographic data storage was performed with high signal-to-noise-ratio reconstruction image, which obtained the storage density of 2 × 108 bits/cm2 for single hologram. Two-photon induced micro-patterns were recorded on the fulgimide/PMMA film with 800 nm, 100 fs, 1 KHz, 50 mW femtosecond laser. Dual-wavelength (650 nm and 488 nm) optical images storage were tested on a two-color mixing fulgides/PMMA film.

Photochromism as a Probe of Gellation in Aluminosilicate Gels Doped with Spirooxazine

Abstract Aluminosilicate gels containing photochromic spiro(1,3,3-trimethylindolo-2,3′-naphth[1,2-b]-1,4-oxazine) were prepared by the sol-gel route, The spirooxazine compound has been used as a photochromic probe for studying the sol to gel transitions of aluminosilicate host gels. Absorption and luminescence spectroscopy were used to elucidate physicochemical changes to the gel network. The photochromic probe compound was found to be very sensitive to local changes that occur during the gel formation process.

‘ACIDICHROMICS’ of Photochromic Spirooxazines

Abstract Acidichromism of four photochromic spirooxazine compounds (SP) were investigated systematically. When hydroxyl group is introduced on the naphtho ring of spirooxazine, the spirooxazine compounds are found to have acidichromic properties in both acidic and basic solutions. Substituent effect on the absorption maximum of acidichromic products has been discussed. A comprehensive discussion of acidichromic, photochromic and thermochromic processes is included.

Synthesis and photochromic mechanism of 3,4-bis[2,5-dimethylthiophene-3-yl]-2,5-dihydrothiophene

Abstract A novel photochromic compound, 3,4-bis[2,5-dimethylthiophene-3-yl]-2,5-dihydrothiophene (BT), has been synthesized. The photochromic reactions of BT in a polar solvent (acetonitrile) and a non-polar solvent (cyclohexane) were investigated by means of steady state absorption spectra and time-resolved transient absorption spectra. The maximum absorption wavelengths of BT in acetonitrile and cyclohexane are at 232 and 233 nm, respectively, and the maximum absorption wavelengths of the photocyclization product (CBT) in acetonitrile and cyclohexane are 445 and 453 nm, respectively. Upon irradiation with ultraviolet light, BT is first excited to the excited singlet state, and then to the excited triplet state via inter-system crossing. Only the excited singlet state generates CBT. The excited triplet state, which has a maximum absorption wavelength at 390 nm, decays rapidly to the starting compound (BT) alone.

Spectral relationship of photoinduced refractive index and absorption changes in fulgide films

Fulgides are one kind of organic photochromic compound, which are famous for their thermal irreversibility. In this report, from the difference spectra of the absorption ΔA(λ) of one kind of pyrrylfulgide, the spectral refractive index change Δn(λ) was calculated by the Kramers–Kronig relation (KKR), and a good correlation of theoretically derived values and the experimental values of the Δn measured by a modified Michelson interferometer was found. Further, it is demonstrated that it was possible to calculate the spectral dependence of diffraction efficiency from the easily accessible absorption changes. This method will be a useful tool for the characterization and optimization of fulgide films. The results show that the diffraction efficiency is high at 488 and 750 nm, where the absorption is very small, so we can realize non-destructive reconstruction.

Experimental study of optical storage characteristics of photochromic material: pyrrylfulgide

Optical data storage is a frontier in the information science. Currently, there are mainly two kinds of storage materials, i.e., thermal-optic and photonic materials. The storage methods are divided into serial and parallel modes. In the market, the mature technique is CD-RW, which uses the thermal-optic material and serial method. The storage density of the CD-RW is restricted by the size of material particles, the conduction of heat, etc. Besides, the recording speed is seriously limited by the process of heating. Photonic materials and parallel method will be the trend in the optical data storage. Because it is based on the photon reaction on the molecule scale, the storage density and speed will be greatly increased. In this paper, a new kind of organic photochromic material -- pyrrylfulgide was studied. A parallel optical data storage system was established. Using the pyrrylfulgide/PMMA film as a recording medium, micro-images and binary digital information could be recorded, readout and erased in this parallel system. The recorded information on the film can be kept for at least 8 months in dark at room temperature. So far, the storage density is 3 x 107 bit/cm2.

STUDIES ON FLUORESCENT SPECIES OF SPIRO-INDOLINONAPHTHOOXAZINES AND THEIR FLUORESCENCE SPECTRA

Photophysical behavior of spiro[1,3,3-trimethylindolino-2,3′-naphtho[2,1-b]-1,4-oxazine] (SP1) and spiro[1,3,3,2′-tetramethylindolino-2,3′-naphtho[2,1-b]-1,4-oxazine] (SP2) were studied. The fluorescent species and their spectra of SP1 and SP2 in polar solvents (acetonitrile and methanol) and non-polar solvent (cyclohexane) were investigated. The fluorescence decay in polar solvents was studied by picosecond time-correlated single photon counting. In most cases, fluorescence decay obeyed triexponential decay kinetics. The major fluorescent species is an excited intermediate which has similar conformation as its precursor (1SP*) formed after the bond cleavage between spirocarbon and oxygen in oxazine ring. The effects of molecular structure and solvent polarity on fluorescence spectra and fluorescence decay lifetime were studied.

Enhancement of a two-photon absorption cross section (TPACS)--design and synthesis of a novel class of photochromic molecules with large TPACS.

Two novel photochromic compounds were designed and synthesized; the two-photon absorption (TPA) cross section of both were measured with a nanosecond laser pulse; their TPACS (delta) values are around 25 x 10(-46) cm4 s photon-1 molecule-1 in acetonitrile; the molecular structure of the target compounds have a 3-methyl-1-benzothiophen-2-yl moiety, which can greatly enhance the two-photon absorption cross section.