Title of Invention

AN IMPROVED PROCESS FOR PREPARATION OF ULTRATHIN FILMS OF METAL PHTHALOCYANINES.

Abstract

The present invention relates to an improved process for the preparation of ultrathin films of metal phthalocyanines. The thickness of the films prepard by the process of the present invention is in the range of 30 to 500 A. The films formed are useful for catalysts, sensors, solar energy conversions etc. The various applications of such films could be catalysis for carbon dioxide photoreduction, solar energy conversions, imaging technology, electronic devices, etc.

Full Text

The present invention relates to an improved process for the preparation of ultrathin films of metal phthalocyanines. The thickness of the films prepared by the process of the present invention is in the range of 30 to 500 A° The films formed are useful for catalysis, sensors, solar energy conversion etc. The various applications of such films could be catalysis for carbon dioxide photoreduction, N02 sensors, solar energy conversion, imaging technology, electronic devices etc. * The conventional methods employed for the formation of ultrathin films of metal-phthalocyanines are: (1) Vacuum Sublimation Technique (2) Langmuir Blodgett Technique (LB) (3) Electrochemical method (4) Organic Molecular Beam Epitaxy (OMBE) The above mentioned methods and their drawbacks are discussed below. (1) Vacuum sublimation technique: The metal phthalocyanine of which ultrathin film is to be deposited is generated in vapor state by sublimating it by giving sufficient energy in an enclosed evacuated space. This is followed by transporting the vapours to the desired substrate, on the surface of which vapor gets condensed/deposited forming a thin film. Drawbacks : High vacuum is required. The process of sublimation being spontaneous, control over thickness of the film formed on the surface of the substrate is difficult. The number of parameters are large to obtain films with desired thickness, uniformity and adharence. (2) Langmuir Blodgett technique : Metal phthalocyanines are modified by preparing a suitable derivative which is soluble in solvent/mixture of solvents. 1x10" to 1x10" M solution of film forming material is formed in a volatile solvent or a mixture of solvents such as benzene, chloroform, carbon tetrachloride, toluene etc, which is delivered on the water subphase. After evaporation of volatile solvent, and water, if present, being absorbed in subphase, the layer of phthalocyanine formed at the interface is compressed to form a continuous film. This film is transferred on a suitable substrate by vertically dipping and withdrawing the substrate with a constant rate and repeating the transfer operation for obtaining the desired thickness of the film. Drawbacks : Peripherally unsubstituted phthalocyanines are not sufficiently soluble to be eligible for LB technique. (3) Electrochemical method : The film formation consists of l)solubilisation of a water insoluble dye by a surfactant 2) oxidative break up of the micelle on electrode surface. 3) release of dye molecule from the aggregates and eventually 4) deposition of dye particles onto electrode surface. Drawbacks : Contamination is unavoidable. (4) Organic Molecular Beam Epitaxy (OMBE) Technique : The vacuum sublimation technique is modified to get ordered films of metal phthalocyanines on ordered substrates such as single crystal metal, layered semiconductors like SnS2, MoS2, ordered graphite, GaAs etc. The modified technique is called organic molecular beam epitaxy (OMBE). If the substrate is amorphous or not ordered as in OMBE, the technique is called OMBD i.e. organic molecular beam deposition. The methodology, advantages and drawbacks are same as for vacuum sublimation technique. (Reference: Phthalocyanines: Properties & Applications, Vol. 1 to 4 Edit. LcznoffC.C. & A.B.P. Lever, VCH Publishers Inc. N.Y. 1989.) The main object of the present invention is to provide an improved method for preparation of ultrathin/thin films of metal phthalocyanines. The principle by which the process of the present invention is developed is based on 1) The formation of metal phthalocyanine solution in a mixture of organic solvent and an alkali/acid which forms miscible phase. 2) The solution as formed in (1) spreads on aqueous subphase, and the organic part evaporates.The examples of such organic solvent being carbon tetrachloride,chloroform, benzene etc. 3) The examples of alkali/acid being NaOH, KOH/H2SO4 respectively. 4)Adjusting the pH of an aqueous phase over which the mixture in 1) is to be spread,effecting metal phthalocyanine precipitation. 5) Since the precipitation reaction takes place only on the surface of the aqueous phase, the solid product obtained can be in the form of a thin film 6) A suitable method for transferring the thin film formed on the aqueous surface to the substrate surface. Accordingly, the present invention provides an improved process for the preparation of ultrathin/ thin films of metal phthalocyanines on substrates which comprises; (a) Preparing a solution of appropriate metal phthalocyanine of which thin film is to be deposited, in a mixture of water immiscible organic solvent having spreading property over water and aqueous solution of inorganic alkali / acid. (bj adjusting the pH of distilled water-subphase to 7 to 10 if acid is used in step (a) or to 4 to 7 if alkali is used (c) Spreading mixture as prepared in (a) on the surface of aqueous phase (b) to form thin film of metal phthalocyanine on the surface of aqueous phase. (d) compressing laterally the film formed with a constant compression pressure after the organic solvent is evaporated by conventional methods, (e) Dipping a substrate on which the film is to be deposited in the solution and withdrawing it from the solution at a uniform rate so that the film is transferred on the surface of the substrate. (f) Repeating the step (e) to obtain desired thickness of metal phthalocyanine film on the substrate. In an embodiment of the present invention, the metal phthalocyanines used in the process may be selected from phthalocyanine of metals Cu, Zn, Fe, Co, Ni, Pt, Pd,Rh, Al and Si. In another embodiment, when the metal phthalocyanine is dissolved in a mixture of aqueous alkali and organic solvent, the pH of the subphse consisting of double distilled water is adjusted in the range 4 to 7. In another embodiment, when the metal phthalocyanine is dissolved in a mixture of aqueous acid and organic solvent, the pH of the subphse consisting of double distilled water is adjusted in the range 7 to 10. In another embodiment of the invention, organic solvents used in the invention may be selected from carbon tetrachloride, chloroform, benzene, n-hexane etc. In yet another embodiment the concentration of aqueous alkali / acid in an organic solvent is such that single phase mixture is formed which spreads on aqueous phase. In another embodiment, the concentration of metal phthalocyanine in a mixture of solvents may be in the range 10-5to 10-3 M . In yet another embodiment the substrates may be selected from glass plates, quartz plates, Si wafers, BaTi03/SrTi03/ A12O3 plates, pellets of ZnO/ ZrO2/MgO etc. In yet another embodiment, the lateral compression of the film may be done by the surface pressure in the range 10 to 30 dynes/cm. In yet other embodiment the rate of dipping and withdrawal of substrate may be in the range 0.5 to 1.5 cms./min. In yet other embodiment acid / alkali may be chosen from H2S04 / NaOH or KOH respectively. The invention is illustrated by the examples given below which should not be construed to limit the scope of present invention. Example I The double distilled water is contained in a Teflon trough 45 times 15 times 2 cms size. The pH is adjusted to 4 by adding sulphuric acid. 5 mg. of Copper phthalocyanine is dissolved in 10 ml. of aquous solution of KOH having a pH of 10. An 0.4 ml. of above solution was added to 99.6 ml of dry carbon tetrachloride so that the solution becomes 3.4 X10-5 M..An o.l ml. of this solution is spread on aqueous subphase of pH 4 to form a film. The film is compressed laterally with the help of oleic acid piston (pressure 30 dynes/cm.) , after evaporation of carbon tetrachloride, a quartz plate 1 times by 1 times by 0.25 cm. was vertically dipped and withdrawn from the solution with a rate Icm./min. transferring the film on the substrate. This operation is repeated thirty times, for increasing the thickness. A film thus formed is characterized by Infrared and Ultra violet -Visible spectroscopy. Example II The double distilled water is contained in a Teflon trough 45 times 15 times 2 cms size. The pH is adjusted to 4 by adding sulphuric acid. 5 mg. of Cobalt phthalocyanine is dissolved in 10 ml. of aquous solution of KOH having a pH of 10. An 0.4 ml. of above solution was added to 99.6 ml of dry carbon tetrachloride so that the solution becomes 3.4 X10-5 M..An o.l ml. of this solution is spread on aqueous subphase of pH 4 to form a film. The film is compressed laterally with the help of oleic acid piston (pressure 30 dynes/cm.) , after evaporation of carbon tetrachloride, a glass plate 1 times by Itimes by 0.25 cm. was vertically dipped and withdrawn from the solution with a rate ,5cm./min. transferring the film on the substrate. This operation is repeated thirty times, for increasing the thickness. A film thus formed is characterized by Infrared and Ultra violet -Visible spectroscopy. The main advantages of the present invention are 1. The method does not require any sophisticated equipment. 2. The method is low cost. 3. The method is very simple and the parameters can easily be monitored. 4. The thickness of the film prepared can be controlled. 5. Uniformity and adherance of the film prepared is good. 6. Large area deposition is possible. 7. The method is useful to deposit ultrathin films. 8. The method would assure purity as the process itself is a purification procedure. WE CLAIM : 1 . An improved process for the preparation of ultrathin/ thin films of metal phthalocyanines on substrates which comprises; (a) Preparing a solution of 0.05% metal phtnaloyamine and the metals selected from cu1 Ni, Pt.pd1 Rh,Al or si solvent having spreading property .over water and aqueous solution of inorganic alkali / acid; (b) adjusting the pH of distilled water-subphase to 4 to 7 if alkali is used in step (a) or to 7 to 10 if acid is used; in a mixture of water immiscible organic (c)preading mixture as prepared in (a) on the surface of aqueous phase (b) to form thin film of metal phthalocyanine on the surface of aqueous phase: , (d) compressing laterally the film formed with a constant compression pressure after the organic solvent is evaporated by conventional methods; (c) Dipping vertically a substrate on which the film is to be deposited in the solution and withdrawing it from the solution at a uniform rate so that the film is transferred on the surface of the substrate selected from glass plates, quarty plate, si wafers, Ba Tip/ Sr Tio3/Al2o3 plates , pelites of Zno/zro2/Mgo; Repeating the step (e) to obtain desired thickness of metal phthalocyanine film on the substrate. 2. A process as claimed in claim 1 , wherein .water immiscible organic solvents having spreading property over water used in the invention is selected from carbon tetrachloride, chloroform, benzene, n-hexane etc. 3. A process as claimed in claimsl and 2, wherein inorganic acid / alkali used, is chosen from H2SO4 / NaOH or KOH respectively. 4. A process as claimed in claims! to 3, wherein the concentration of aqueous alkali / acid in an organic solvent is such that single phase mixture is formed which spreads on aqueous phase. 5. A process as claimed in claims l to 4, wherein the concentration of metal phthalocyanine in a mixture of solvents may be in the range 10" to 10" M 6. A process as claimed in claims1 to 5, wherein the lateral compression of the film may be done by the surface pressure in the range 10 to 30 dynes/cm. 7. A process as claimed in claims1 to 6, wherein the substrates may be selected from glass plates, quartz plates, Si wafers, BaTiO3/ SrTiO3/ A1203 plates, pellets of ZnO/ ZrO2/MgO etc. 8. A process as claimed in claims 1 to 7, wherein the rate of dipping and withdrawal of substrate may be in the range 0.5 to 1.5 cms./min. 9. A process for the deposition of ultrathin films of metal phthalocyanines described substantially hereinbefore and illustrated with reference to the examples.

Documents:

2517-del-1998-abstract.pdf

2517-del-1998-claims.pdf

2517-del-1998-correspondence-others.pdf

2517-del-1998-correspondence-po.pdf

2517-del-1998-description (complete).pdf

2517-del-1998-form-1.pdf

2517-del-1998-form-19.pdf

2517-del-1998-form-2.pdf