[Quinone.com] Electronic and photochemical fields

Applications, physical properties and features

Electronic and photochemical fields

1.physical properties and features of anthracene

Molecular formula : C₁₄H₁₀, Melting point : 217~218

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Boiling point : 340

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Plate crystal, monoclinic molecular crystal
Aromatic hydrocarbon with 3 benzene rings and 14 pi electrons.
Single crystal: Colorlessness,
Birefringence (double refraction) : large,
Resistivity : 1020Ω cm ( room temperature )
Dissolves in benzene, toluene, chloroform, tetrachloromethane, alcohol, ether
Pure anthracene is colorless and has violet fluorescence.
It shows yellow color and green fluorescence, when it contains impurities such as tetracene.
Raw material of alizarin.
Two anthracenes form the dianthracene combined in each 9,9'- and 10,10'- position by light (310nm or 375nm), unlike benzene and naphthalene.

2.Anthracene derivatives in organic semiconductor field

    Carriers (electron, positive hole and exciton) can move comparatively smoothly in acene single crystals such as anthracene, tetracene and pentacene.
    They belong to the semiconductor, in view of their electric conductivity.
    Their crystal structures have overlaps of pi orbitals, and the band similar to inorganic semiconductor is formed, so the carrier can move of interband.
    It is observed that there is an active type electric conductivity decreases with reduced temperature or there is a type electric conductivity seldom depends on the temperature, on the thin film of acene single crystal formed by vapor deposition.
    And, pressure dependency of carrier mobility is detected in anthracene crystals. When the pressure is high, the carrier mobility increases, since the molecule intervals decrease and overlaps of molecular orbital increase.

The volume resistivity [Ω cm]

conductor
metal

semiconductor
inorganic	Ge,Si,CuO,Se
organic	anthracene

insulator
Polymer	polyethylene

    Organic semiconductor is practically used in copying machine, photoconductor of laser printer, liquid crystal display unit and resist (photo resist), and additional application development utilizing its characteristic is expected.
    Organic semiconductor application of anthracene and phthalocyanine has advantages like low price, high flexibility, possiblity of large scale device, easy to make thin, wide wavelength range as optical device, light weight, non-polluting and no toxicity.
    However, as organic compounds, it has demerits such as weakness to heat or external force, and their electric current is small because of the small of carrier mobility and density, and the stability is not enough.
    The development of low cost solar cell is expected as an application field of organic semiconductor, for example polymer matrix molecular film of organic semiconductor is manufactured by the spin coating method for low cost solar cell.
    And the development of electro luminescence device ( organic EL device ) is expected too. Targets are improvements of a thin film display of multicolor, high brightness and self luminescence type, higher brightness of doping, and an uniformity of light emission by decrystallization (amorphous).

3.Optical absorption and anthracenes

    Materials radiate the light at high temperature like an electric lamp, but some materials radiate the light by some kind of stimulation even at low temperature. This is called the luminescence ( light emission ). The materials that are absorbing the energy radiate the various lights. The luminescence is not the light that is radiated with thermal radiation,Cerenkov effect, Raman effect and Rayleigh scattering.
    The fluorescence is the light emission by the electron transition between equal multiplicity states.
    The phosphorescence is not so.
When an electron is excited at excited level, then it falls in the lower energy level, and finally it returns to the ground state.
    The frequency of the light emission is generally smaller than that of the absorbed light, because a molecule consumes the part of the absorbed energy as a molecular vibration. (Stokes'law)
    Important informations about an emission mechanism or light emission material is understood from spectra, polarization properties, afterglow characteristics, attenuation characteristic, effects of electric field and magnetic field, temperature dependency, excitation wavelength dependence, excitation time dependence, etc.
    Generally aromatic hydrocarbons have fluorescence, especially anthracenes are famous as organic substances with fluorescence.
    It is possible that the molecule of the excitation state gives the energy to other molecule without emitting light like an electron transport system in photosynthesis.
    Photosensitization electron transfer which gives the energy (electron) of optical absorption to other molecule has been applied in many fields such as printing, painting, optical lens, dental materials, plastic molding, optical disks, metal surface processing, UV (ultraviolet ray) and EB (electron beam) polymerization.
    The development of UV initiated cationically polymerizable compound, reactive diluent, photoinitiator and sensitizer which shows the excellent physical property (high thermo stability, high glass transition temperature, high insulation, low dielectric constant) in each field have been required.
Many anthracene derivatives are utilized in such field.

Absorption spectrum of 9,10-dibutoxyanthracene

4.Absorption and hardening

    These days, the UV hardening system is introduced in a lot of industries such as paint, ink, resist and an adhesive. Most popular photo-curing process is performed by radical polymerization using acrylic monomers.
    But process of radical polymerization has weak points such as bad dimensional stability and easy termination of chain reaction because by the oxygen in the air.
    The process of cationic polymerization does not have above weak points, so it has gradually become to be used in light molding which needs dimensional accuracy.     Because of slow hardening rate of cationic polymerization compared to radical polymerization, cationic process was used in special applications such as DVD.
    Now by using anthracene derivatives as sensitizers, cationic polymerization becomes to be used especially in can-coating. Because anthracene derivatives have a maximum absorption at 254 nm and a moderate absorption from 350 to 410 nm, and have high efficiency of energy transfer to the photo-initiator, they are best fit as sensitizers.
    KAWASAKI KASEI CHEMICALS LTD. has developed anthracene derivatives such as dibutoxyanthracene and dipropoxyanthracene as excellent photo sensitizers for such photo-curing process, and now began to supply to the market.

5.Quinone derivatives in magnetic disk application

    In magnetic recording disk (hard disk, floppy disk) which are mass storage media used in personal computer, network server, movie server, etc., ferromagnetic film with highly recording density is formed on the surface of nonmagnetic substrate by sputtering method. And, generally a protective film of an amorphous carbon is formed on the ferromagnetic film, and a lubricant layer is applied on the protective layer in order to enhance the slide-proof and corrosion resistance.
When high-temperature condition, perfluoropolyether tends to vanish, caused by sliding of the surface with the magnetic head, and gradually the lubricant property becomes lower.
    To solve such problem, they propose the technology to use the lubricant like perfluoroalkylether having terminal group which works as an anchor scratching to the protective layer.
    Such magnetic recording disk shows excellent fugitiveness-proof and slide-proof, since the terminal group of the lubricant adheres to the surface of protective layer by anchor ability.
    Though the surfaces of magnetic head and magnetic disk seem to be flat, they are uneven in nano-order. They penetrate and contact each other through the lubricant film of nano-order thin film.
    At the contact point, the temperature rises instantly over several hundred, then exoelectrons are generated from the head or the disk.
    It becomes evident that a continuous decomposition of the lubricant is induced by the anion radical which is formed by adhering generated exoelectrons to lubricant molecules.
    However, if the lubricant film which is composed of mixture of electron acceptors, is formed on the protective film, exoelectrons generated from the contact point will be trapped by the electron acceptor with strong electrophilicity, so exoelectrons become hard to adhere to the lubricant molecules.
    The exoelectrons trapped acceptor become anion radicals and the anion radicals become stable, but a chain reaction no longer occurs.
In short, it is possible to prevent the fluorine lubricant decomposition caused by the exoelectrons at the contact point. As electron acceptors, you can quote quinones such as p-benzoquinone, o-benzoquinone, bianthrone, benzoanthraquinone, 1,2-naphthoquinone, 1,4-naphthoquinone and anthraquinone.

6.Photo resist and quinones

A composition which contains a quinone diazide unit and an alkali-soluble resin is used as a positive resist composition reacting to the radiation such as ultraviolet ray, far ultraviolet ray, electron beam, ion beam, X-ray, etc.
This composition is used as a positive resist because it changes to the alkali-soluble form from the alkali-insoluble form by generating the carboxyl group with decomposition of quinone diazide by the photo irradiation of 300nm~500nm wavelength. The positive resist is promising that the resolution is remarkably higher than one of the negative resist, so it is utilized for the production of integrated circuits such as IC and LSI.
Quinone diazide compounds are for example 1,2-benzoquinonediazido-4-sulfonate, 1,2-naphthoquinonediazido-4-sulfonate, 1,2-naphthoquinonediazido-5-sulfonate, etc.

7.Liquid crystal and anthracenes

    By the addition of the specific dopant in a nematic liquid crystal and a cholesteric liquid crystal that displays and retains the focal conic condition as the cholesteric phase and the homeotropic condition as the nematic phase with same voltage, it is possible to raise the electro-optical hysteresis effect. And it is possible to work stable with high contrast ratio, large display capacity and ability of type-in writing. The dopant compounds are the most suitable that the compound affects orientation regulation force between liquid crystal molecules and that is non-liquid crystal organic compounds, aromatic groups, the molecular flat structure and the electro-donicity.
    There are bianthrone, 1,2,5,6-dibenzanthracene, 9,10-diphenylanthracene, 1,2,3,4-dibenzanthracene, 5,6,11,12-tetraphenylnaphthacene, etc. on such organic compounds.

    dielectric constant(permittivity), dielectrics, relative dielectric constant, insulating materials, insulation resistance, dielectric characteristic, permeability, conductivity, frequency, nonlinear optical property, integrated circuit, tunnel effect, dipole moment, lattice constant, Miller Index, forbidden band, permission band, Brillouin zone, HOMO (highest occupied molecular orbital), LUMO (lowest unoccupied molecular orbital), polarization, internal electric field, absorption, hysteresis loop, phase transition, spontaneous polarization, Curie point, piezoelectric effect, electrooptic effect, Elasticity optic effect, oscillation, adulterant effect, photoconduction, induced current, Zener effect,     Schottky effect, Poole-Frenkel effect, recombination, lattice defect, etching, Liquid crystal, redox (oxidoreduction),
electrochromic, photochromic, electron-withdrawing, electro-donicity, polarizability, photo-electric effect