GB2083488A - Light-sensitive dyestuffs - Google Patents

Abstract

Compositions for use in photogalvanic cells comprising as light-sensitive compounds heterocyclic compounds according to the general formula <IMAGE> wherein n, X, R<1>, R<2>, Y<1>, Y<2>, Y<3>, Z<1>, Z<2>, Z<3>, Z<4>, B and m having defined meanings. The compounds of this general formula (I) with the exception of 3,7-bis(4- methyl- 1 -piperazinyl)phenothiazonium bromide are claimed per se.

Description

SPECIFICATION Light-sensitive compounds and compositions The present invention relates to compositions for use in photogalvanic cells comprising one or more heterocyclic compounds as light sensitive compounds(s).

The present invention also relates to novel heterocyclic compounds which may exhibit interesting properties as dye-stuffs for various uses and which may also exhibit photo-reducible activities which render them very suitable for use in photogalvanic cells to convert incident light into electricity. Finally, the present invention also relates to photogalvanic processes comprising one or more of the heterocyclic compounds according to the present invention as the photogalvanically active compound(s).

The present invention thus provides compositions for use in photogalvanic cells which comprise as light-sensitive compounds heterocyclic compounds according to the general formula:

wherein n is O or 1; X represents a moiety NR3, O, S, SO, Se or CR3R4 wherein R3 and R4 which may be the same or different each represent an alkyl group having up to 6 carbon atoms which may contain one or more nitrogen moieties or a heterocyclic ring structure having up to three nitrogen and/or oxygen atoms in the ring; at least one of R' and R2 represents a N-containing alkyl group, and the other, if any, represents a hydrogen atom or a (N-containing) lower alkyl group or R' and R2 together with the nitrogen moiety to which they are attached form a ring-structure

### which may contain up to two nitrogen and/or oxygen moisties or a group NH, NR5,NH2, NHR5, or NR5R5 wherein R5 and R5 which may be the same or different each represent a hydrogen atom or a (Ncontaining) lower alkyl group, the total number of carbon atoms in the ring II, which may contain up to two double bonds, being of from 2 up to and including 6;; yr, Y2 and Y3 which may be the same or different each represent a hydrogen atom, a halogen atom, a cyano, lower alkyl, lower alkoxy or 0+ carboxylate group or a group NP7P5, NHR7R8 or NR7R3R9 wherein R7 and R3 which may be the same or different each represent a hydrogen atom or a (N-containing) lower alkyl group or R7 and R3 together with the nitrogen moiety to which they are attached form a ring-structure

3 which may contain up to two nitrogen and/or oxygen moieties or a group NH, NR5, NH2, NHRs or NR5R6 wherein R5 and R5 are as defined hereinbefore, the total number of carbon atoms in the ring Ill, which may contain up to two double bonds, being of from 2 up to and including 6, and R9 represents a hydrogen atom or a lower alkyl group; z1, Z2, Z3 and Z4 which may be the same or different each represent a hydrogen atom, a cyano, lower alkyl, lower alkoxy or carboxylate group or a group NR7R8, NHR7R8 or NR7R8R9 wherein R7, R8 and R9 are as defined hereinbefore; B represents an anion and m is a whole number matching the electroneutrality, the o-chinons as well as the corresponding dihydrochinoids.

It will be understood that o-chinons according to the present invention are compounds according to the general formula I wherein the moiety

is attached to the carbon atom designated 1 in the formula I thus forming an o-chinoid structure with the nitrogen atom bridging the two carboxylic six-membered rings. It will further be understood that the expression "corresponding dihydrochinoids" refers to compounds according to the general formula I wherein the bridging nitrogen atom carries at least one hydrogen atom and the group

is connected via a single bond to the six-membered ring, either at position 3 or 1.

The present invention relates in particular to compositions comprising heterocyclic compounds according to the general formula I wherein n is 1; X represents a moiety 0, S. SO, or Se; at least one of R' and R2 represents a N-containing lower alkyl group, and the other, if any, represents a hydrogen atom or a (N-containing) lower alkyl group or R' and R2 together with the nitrogen moiety to which they are attached form a ring-structure Il which may contain two nitrogen and/or oxygen moieties or a group NH, ### NR5, NH2, NHR5 or NR5R5 wherein R5 and R5 which may be the same or different each represent a hydrogen atom or a lower alkyl group which may or may not contain a nitrogen atom, the total number of carbon atoms in the ring II, which may contain up to two double bonds, being 3, 4 or 5; Y', Y2 and Y3 which may be the same or different each represent a hydrogen atom, a cyano, methyl or lower alkoxy , &commat; group or a group NR7R8, NHR7R8 or NR7R8R9 wherein R7 and R8 which may be the same or different each represent a hydrogen atom or a N-containing alkyl group or R7 and R8 together with the nitrogen atom to which they are attached form a ring-structure III which may contain up to two nitrogen and/or oxygen 00 (3 moieties or a group NH, NR5, NH2, HR5 or i9R5R5 wherein R5 and R5 which may be the same or different each represent a hydrogen atom or a lower alkyl group which may or may not contain a nitrogen atom, and R9 represents a hydrogen atom or a lower alkyl group; Z1, Z2, Z3 and Z4 which may be the same or different each represent a hydrogen atom, a halogen atom, a cyano, methyl or lower alkoxy group or a 0+ group NR7R8, NMR7Ru or NR7R8R9 wherein R7, R8 and R9 are as defined hereinbefore; B represents a halide, (hydro)sulphate, (hydro)phosphate, nitrate, fluoroborate or perchlorate and m is an integer matching the electroneutrality, the o-chinons and the corresponding dihydrochinoids.

Particularly preferred compositions according to the present invention are those comprising heterocyclic compounds according to formula I wherein n is 1; X represents an oxygen, sulphur or selenium moiety; R' and R2 both represent a N-containing alkyl group having up to 6 carbon atoms or R1 and R2 together with the nitrogen moiety to which they are attached form a ring-structure II which also contains one or two oxygen and/or nitrogen moieties or a group NR5 wherein R5 represents a hydrogen atom or a lower alkyl group, especially a methyl group, the total number of carbon atoms in the ring II, which may contain up to two double binds, being 3 or 4;; Y1, Y2 and Y3 which may be the same or 0+ different each represent a hydrogen or halogen atom or a group NR7R8 or NHR7R8 wherein R7 and R8 both represent a N-containing alkyl group having up to 6 carbon atoms or R7 and R8 together with the nitrogen moiety to which they are attached form a ring structure Ill which may contain up to two nitrogen and/or oxygen atoms or a group NR5 wherein R5 represents a hydrogen atom or a lower alkyl group, especially a methyl group, the total number of carbon atoms in the ring III being 3 or 4, Z', Z3 or Z4 which may be the same or different represent a hydrogen or halogen atom and Z2 represents a (3+ hydrogen or halogen atom, or preferably a group NR7R8 or NHR7R8 wherein R7 and R8 are as defined hereinbefore; B represents a halide, sulphate, fluoroborate or perchlorate and m is an integer matching the electroneutrality. Heterocyclic compounds according to the general formula I with the exception of 3,7-bis (4-methyl-1 -piperazinyl) phenothiazonium bromide appear to be novel compounds.

Examples of compounds to be used in the compositions according to the present invention are salts, especially the halides of 3-substituted and 3,7-disubstituted phenothiazines (n = 1, X = S) such as: 3-morpholino-phenothiazine, 3,7-bis (morpholino) phenothiazine, 3-(4-methyl-i -piperazinyl) phenothiazine, 3,7-bis (4-methyl-l -piperazinyl) phenothiazine, 2chlorn-3,7 bis (4-methyl-1- piperazinyl) phenothiazine, 3-(1-imidazolyl) phenothiazine, 3,7-bis (1-imidazolyl) phenothiazine, N,N-bis (3-dimethylaminopropyl) phenothiazine-3-amine, N,N,N',N',-tetrakis (3-dimethylaminopropyl) phenothiazine-3,7-diamine, N,N-bis (2dimethylaminoethyl) phenothiazine-3-amine, N,N,N',N'-tetrakis (2-dimethylaminoethyl) phenothiazine-3,7-diamine, N-methyl-N(2-dimethylaminoethyl) phenothiazine-3-amine, N,N'-dimethyl-N,N'-bis (2-dimethylaminoethyl) phenothiazine-3,7-diamine, 3-substituted and 3,7-disubstituted phenoselenazines, 3-substituted and 3,7-disubstituted phenooxazines and 3-substituted and 3,7-disubstituted phenothiazine-5,5 dioxides such as 3-(4 methyl-1-piperazinyl) phenoselenazine, 3,7-bis (4-methyl-i -piperazinyl) phenoselenazine, 3-(4-methyl 1-piperazinyl) phenothiazine 5,5-dioxide and 3,7-bis (4-methyl-1-piperazinyl) phenothiazine-5,5dioxide; as well as the salts of the corresponding o-chinons and the dihydrochinoids.

Preferred examples of the compounds to be used in the compositions according to the present invention are the salts of 3-piperazinyl substituted and 3,7-bis-piperazinyl substituted phenothazines, especially the piperazinyl-substituted phenothiazonium chlorides.

The heterocyclic compounds can be prepared by methods well known to those skilled in the art. It has been found convenient to use the appropriate (unsubstituted) heterocyclic compounds i.e.

carbazole, phenazine, phenoxazine, phenothiazine, phenothiazine 5,5-dioxide, phenoselenazine or acridine as the starting materials. A suitable method for preparing 3,7-bis substituted heterocyclic compounds comprises the oxidation of the appropriate starting material as referred to hereinabove with bromine or Fe (III)-chloride in the presence of compounds containing the nitrogen-containing group(s) te be introduced into the starting material.It has been found that Fe(IlI)-chloride is very useful in the oxidation-procedure when a cyclic nitrogen moiety has to be introduced into the starting material such as piperazine, N-methylpiperazine or morpholine, whereas bromine is the best oxidator when acyclic, linear or branched, nitrogen containing moieties are to be introduced into the starting heterocyclic compound.

Depending on the purity of the starting material, the compounds can be prepared with high purity ( > 90%, usually > 95%). It may be necessary to subject the starting material to one or more purifications - treatments since commercially available starting materials may contain rather large amounts (e.g. amounts of up to 20% or even more) of impurities which normally cause severe problems when used as light-sensitive compounds.

The compounds can be characterized by several analytical techniques, e.g. chemical ionization mass spectrometry (MS), N.M.R. spectroscopy and thin layer chromatography (TLC). The compounds can also be characterized by the wave length(s) at which they exhibit the highest absorption (measured in water at a set pH) and the appropriate coefficient of extinction.

The compounds according to the present invention are of interest as they can be applied as dyestuffs, indicators and, in particular, as compounds being capable of photo-reductivity, i.e. for use as photo-reducible compounds in photogalvanic cells. It should be noted, however, that photo-reducible compounds do not require to be dye stuffs, the basic requirement appears to be the capability of undergoing a reasonable, endergonic photochemical redox-reaction in response to illumination with sunlight, as well as reversible redox electrode reactions.

The use of phenothiazine and related compounds as light-sensitive compounds for photogalvanic processes has been described (see e.g. British Patent Specification 1 ,557,627). It is known from J.

Electrochem Soc. 125,1365-1371(1978) thatdisulphonated phenothiazines although much more soluble in water than phenothiazine itself exert a lower level of activity. Also the light-activity of the known compound N,N,N',N'-tetrakis (2-hydroxyethyl) phenothiazonium bromide - apparently almost totally miscible in water -- (see Proc. of the 3rd Intern. Conf. on Photochemical Conversion and Storage of Solar Energy, 3.8.80, page 243) does not exceed the activity of phenothiazine as Iight-sctive material. It thus appears that the conversion of radiation into electric energy occurs with a rather low efficiency in the photogalvanically active systems described thusfar.This may be due to a variety of reasons since a number of extremely complex photochemical and electrochemical reactions take place during the conversion processes. Also undesired side-reactions will have an adverse effect on the current yields, which is also influenced considerably by the shape of the cell, the electrodes used, the impurities present in the photo-reducible compound applied and the redox-couple involved.

Without being bound to any particular theory, it would appear that the structure of the photo reducible compound may play an important role in improving the efficiency of the photogalvanic cell. It is surprising and not yet completely understood that the structural features of the heterocyclic compounds according to the present invention contribute so markedly to the photogalvanic activity of the known phenothiazine-type compounds. It has also been found that the compounds are stable, especially in acidic media which renders them very useful as light-absorbing compounds in photogalvanic cells.

Photogalvanic cells have been described in the art and it is therefore not necessary to give a detailed description. It will be clear that a photogalvanic cell is essentially a combination of a photochemical and an electrochemical device capable of converting in a direct way radiation (e.g. solar energy) into electricity. It is therefore an electrochemical cell containing a light-sensitive material.

Excitation of this material by a photon induces a chemical reaction in the electrolyte solution as a result of which high-energy products are formed. These products release their energy in the form of electricity by a reaction at the electrodes contacting the electrolyte solution. The light-sensitive material is present in solution. When the cell is irradiated in such a way that at least part of the converted heterocyclic compounds can reach one electrode, a potential difference between light and dark electrode will occur and current may be drawn from the cell. In principle the cells is cyclic and can be used indefinitely, which means that solutions should be used which exhibit a degree of reversibility which is as large as possible.

Suitable redox-coupies to be used in the photogalvanic process comprise Fe(ll)/Fe(lil) systems, chinon-hydrochinon systems as well as systems based on Co-chelates having different valencies. Good results have been obtained using Fe(ll)SO4/{Fe(111)|2(SO4)3 as the redox-couple. Normally the lower valence partner of the redox-couple (i.e. the reductor) will be present in a much higher concentration that the higher-valence partner of the redox-couple (i.e. the oxidator). The optimum concentration ratio will depend on several factors including the specific composition of the solution applied, the solvent and the pH of the system employed. Normally ratios of from 10 to 250 can be applied.

The photogalvanic cells are normally operated at a pH below 7, preferably at a pH between 1 and 5, most preferably at a pH between 2-4. Acids commonly used to obtain the desired pH comprise hydrochloric acid, sulphuric acid, perchloric acid. Hydrogen fluoroboric acid and phosphoric acid. When using a redox-couple based on sulphates such as the Fe(ll)/Fe(lil) couple, sulphuric acid is the preferred acid. Good results can be obtained by operating the cell under virtually oxygen-free conditions, i.e. the solution should preferably contain less than 10 ppm dissolved tree oxygen.

The preferred solvent for photogalvanic solutions according to the present invention is water as it appears that the compounds according to the present invention exhibit a rather good solubility in this solvent. Other solvents which do not or not substantially affect the photogalvanic process may also be used, e.g. acetonitrile as well as mixtures of acetonitrile and water in any proportion to the extent that the compounds according to the present invention are soluble in such mixtures to an acceptable amount, i.e. amounts at least as high as 10-3 mol/l, and preferably even higher.

It may be beneficial to include a complexing agent in the photogalvanic solution. Although the exact role of the complexing agents is not yet completely understood it would appear that they prevent or minimize undesired dark reactions by complexing with the higher-valence partner of the redox-couple applied. For instance, when 3,7-bis (4-methylpiperazinyl) phenothiazonium chloride is the light activated compound and Fe(lil/Fe(lil) the redox-couple it is thought that the semiphenothiazonium radical is formed and that the last step in the production of electricity is the oxidation of leukophenothiazonium ions at the light-electrode together with the reduction of Fe(IlI) to Fe(ll) at the dark electrode.It is thought that the semiphenothiazonium radical and Fe(lll) are formed in the solution by electron transfer from excited 3,7-bis (4-methylpiperazinyl) phenothiazonium chloride to Fez+. The leukophenothiazonium ion is formed by dismutation of the semi-phenothiazonium radical. The efficiency of the cell decreases when in the dark bulk undesired reactions occur resulting in the oxidation of leukoand/or semi-phenothiazonium ions and in the reduction of Fe(IlI) to Fe(ll).

Complexing agents which can be suitably used comprise amongst others fluorides, phosphates, salts of dibasic organic acids as well as amino acids and salts thereof such as 2-amino-propionic acid and salts thereof. Good results have been obtained using sodium fluoride, sodium phosphate, alkali salts of citric acid, sodium oxalate, ammonium oxalate and 2-amino-propionic acid. It has been found that sodium fluoride and, sodium phosphate exhibit the most profound effect of the compounds tested thusfar. Also combinations of complexing agents can be used. The complexing agents can be suitably added in amounts of from 0.1 to 50 times the concentration of the higher-valence partner (oxidator) employed.Good results have been obtained using amounts of from 1 to 20 times the molar concentration of the linher-valence partner (oxidator) or the redox-couple employed.

Since the heterocyclic compounds as described hereinbefore exhibit a rather good solubility in water, sometimes even as high as 10-' mol/l, they are extremely useful as light-sensitive compounds in photogalvanic processes when water is used as the solvent. It may not even be necessary to use the heterocyclic compounds according to the present invention to the limit of their respective solubilities which makes the photogalvanic system much more flexible as reagents to temperature and other practical conditions. Normally, the experiments described herein have been carried out conveniently using the heterocyclic compounds in concentrations of about 10-2 - 2.10-2 mol/l..

Any electrodes which are normally applied in photogalvanic processes can be used in combination with the heterocyclic compounds according to the present invention. Suitable light electrodes comprise electrodes based on platinum, gold, carbon, titanium dioxide and SnO2 which may be coated to appropriate substrates by techniques known to those skilled in the art. If desired, transparent electrodes can be used. Suitable dark electrodes comprise platinum, indium-tinoxide and carbon in various forms and shapes such as wires, gauzes or cloth or thin layers. The experiments described herein have been mostly carried out using a SnO2 light-electrode and a platinum-gauze or coal-type dark-electrode.

During the course of the experiments it has been observed that it may be very beneficial to increase the surface area of the dark electrode compared to that of the light electrode. It may be useful to increase the surface area ratio with a factor 5 or even higher. Especially when using carbon dark electrodes, such as carbon felt or carbon cloth, the power to be drawn from the cell can be increased considerably. Without wishing to be bound to any specific theory, it would appear that this effect occurs when the dark electrode is used under conditions wherein it behaves as the current-limiting electrode.

An increase in its surface area would then allow more ions to be discharged which would cause an increased current and hence an increased power of the photogalvanic cell.

It is also possible to use more than one heterocyclic compound in photogalvanic solutions to be used in photogalvanic processes. Preference should be given to those combinations of heterocyclic compounds which together cover a broader region of the visible spectrum in order to absorb more incident light. Also combinations of one or more heterocyclic compounds with one or more known photogalvanically active compounds may be used provided the solubility of such complex system is still acceptable. If desired, it is also possible to use one or more photosensitizing dyes, e.g. rhoda mine, in the solutions according to the present invention.

The present invention further relates to novel heterocyclic compounds which may exhibit interesting properties as dye stuffs and which may also exhibit photoreducible activities which render them very suitable for use in photogalvanic cells which comprise at least a heterocyclic compound as defined hereinbefore. The present invention thus relates to heterocyclic compounds according to the general formula I with the exception of 3,7-bis (4-methyl-i -piperazinyl) phenothiazonium bromide. The present invention also relates to photogalvanic processes comprising one or more of the heterocyclic compounds as defined hereinbefore as the photogalvanically active compound(s).The present invention relates in particular to photogalvanic processes comprising at least 3,7-bis (4-methyl-1 -piperazinyl) phenothiazonium chloride as the photogalvanically active compound.

The invention will now be illustrated by the following Examples: EXAMPLE 1 Preparation of 3,7-bis (4-methyl-i -piperazinyl) phenothiazonium dichloride To a stirred solution of 20 g (0.1 M) phenothiazine, 22 g (0.22 M) of N-methylpiperazine and 60 g of anhydrous sodium carbonate in dry methanol (1 litre) were added 106 g (0.66 M) of anhydrous Fe (III)-chioride over a period of 25 minutes at 500 C. Thereafter the reaction mixture was stirred for 45 minutes, heated to reflux and filtrated while hot. After cooling the filtrate, diethylether (1 litre) was added thereto and the mixture was then filtered. The crystals obtained were dissolved in 10% hydrochloric acid (0.5 litre), the solution filtered and isopropanol (5.5 litres) was added thereto.The solution obtained was cooled to 200 C. The crystals obtained were filtered off and then washed with two equal portions of isopropanol (G.1 litre) and twice with diethylether (0.1 litre) and finally dried in a stream of nitrogen.

The yield of 3,7-bis (4-methyl-i -piperazinyl) phenothiazonium dichloride was 12 g (23% calculated on starting phenothiazine). The structure of the compound was confirmed using N.M.P. - and chemical ionization Mass Spectrometry. The purity of the product was > 95% as determined by Thin Layer Chromatography. The following absorption data were measured: absorption maximum (visible region) at 640 nm (water, pH = 1.7). The coefficient of extinction at 640 nm was 59.000.

EXAMPLE 2 Preparation of 3,7-bis morpholino phenothiazonium dichloride.

Phenothiazine (5 g, 25 mmol) was dissolved in glacial acetic acid (100 ml). A solution of bromine (12 g, 75 mmol) in glacial acetic acid (200 ml) was added over a period of 5 minutes. The. crystals obtained were filtered off and then rinsed with acetic acid (20 ml). The filtrate was then suspended in 96% ethanol (100 ml) and morpholine (18 g, 200 mmol) in ethanol (200 ml) was added over a period of 5 minutes under stirring which was continued thereafter for 10 minutes. The ethanol was then removed by evaporation and the residue obtained rinsed with diethyl ether (100 ml) and mixed with water (300 ml) and MgCI2.6H2O (150 g). This solution was continuously extracted with dichloromethane for 20 hours. Thereafter, dichloromethane was evaporated from the solution obtained. The residue was then dissolved in chloroform (300 ml).This solution was filtered and concentrated to a volume of about 70 ml. After the addition of diethyl ether (200 ml) crystals were obtained. The mixture was filtrated and the remaining crystals rinsed with ether (50 ml) and dried. 1.1 g of product was obtained. The structure of the compound was characterized using chemical ionization Mass Spectrometry. The coefficient of extinction at the absorption maximum of 665 nm (pH = 1.8) was 56.000.

EXAMPLE 3 Preparation of 3,7-bis (4-methyl-i -piperazinyl) phenoselenazonium dichloride.

To a stirred solution of 20 g (0.1 M) phenoselenazine 22 g (0.22 M) of N-methylpiperazine and 60 g of anhydrous sodium carbonate in dry methanol (1 litre) were added 212 g (1.32 M) of anhydrous Fe (III)-chloride over a period of 45 minutes at 500 C. Thereafter the reaction mixture was stirred for 45 minutes and filtrated. The residue was dissolved in 10% hydrochloric acid (0.5 litre). The solution obtained was filtered and isopropanol (5.5 litres) was added thereto. The solution was cooled to -200C.

The crystals obtained were filtered off and then washed with two equal portions of isopropanol (0.1 litre) and twice with diethylether (0.1 litre) and finally dried in a stream of nitrogen.

The yield of 3,7-bis (4-methyl-i -piperazinyl) phenoselenazonium dichloride was 7 g. The structure of the compound was confirmed using chemical ionization Mass Spectrometry. No major impurities could be detected using Thin Layer Chromatography. The following absorption data were measured: absorption maximum (visible region) at 648 nm (water, pH = 2). The coefficient of extinction at 648 nm was 59.000.

EXAMPLE 4 Preparation of the dichloride ofi\N,N',N'-tetrakis {3-dimethylaminopropyl) phenothiazine-3, 7-diamine.

To a stirred solution of 1,2 g (6 mmol) phenothiazine, 2 g (11 mmol) of bis (2 dimethylaminopropyl) amine and 6 g of anhydrous sodium carbonate in dry methanol (50 ml), 3 g (18 mmol) bromine was slowly added at a temperature of about 500 C. Thereafter the reaction mixture was stirred, heated to reflux and filtered while hot. After cooling the filtrate, diethylether (50 ml) was added thereto and the mixture was then filtered. The crystal mass obtained was dissolved in 10% hydrochloric acid (25 ml), the solution filtered and isopropanol (275 ml) was added thereto. The solution obtained was cooled 200 C. The crystal mass obtained was filtered off and then washed with two equal portions of isopropanol (5 ml) and twice with diethylether (5 ml) and finally dried in a stream of nitrogen.The structure of the compound was characterized using chemical ionization Mass Spectrometry.

absorption maxima (visible region) at 650 nm (water, pH = 4) and 650 nm (water, pH = 2.2). The coefficient of extinction at 650 nm was 59.000.

In the experiments described in the following Examples the photogalvanic activity of some of the heterocyclic compounds according to the present invention as light-sensitive compounds is described.

The photogalvanic experiments using heterocyclic compounds according to the present invention as light-sensitive compounds were carried out in photogalvanic cells specially designed to handle rather concentrated solutions of the appropriate compounds. In principle, the photogalvanic cells used comprise a cell body, e.g. a rectangular or cubic cell body, at least one wall thereof consisting of transparent materials such as glass. A very suitable cell comprises a cubic cell body having edges of 20 mm. The dark electrode is placed within the (cubic) structure at a predetermined distance from the light electrode. The light electrode normally consists of a thin layer of light electrode material placed or coated on the inside surface of a transparent cell wall.

The cell body is then filled with the appropriate solution through a tube connected with an opening in the upper surface of the cell body which is otherwise sealed off. This tube also provides access for the reference electrode. In the experiments described hereinafter, a standard calomel electrode was used as the reference electrode. By filling the cell body and the tube exceeding therefrom with the photogalvanic solution and purging the system thus obtained with nitrogen or another inert gas, or by first purging the cell body with nitrogen or another inert gas followed by addition of the solution under an inert atmosphere, the cell becomes ready for experimental purposes.The wires from the electrodes are circuited in such a way that the voltage difference between dark and light electrodes (expressed as Vdl), the maximum current through the system (imax) and the potentials of the respective electrodes can be monitored. From these readings the maximum power delivered by the cell (expressed as P max) can be calculated taking into account the so-called fill-factor (ff) which for the experiments described hereinafter is between 30 and 50%.

All the experiments described hereinafter were carried out using Fe(ll)SOd(Fe(lll)j, (SO4)3 as the redox-couple (in the concentrations indicated) and sulphuric acid to obtain the desired pH. The solvent was water.

Two types of light-electrodes were used in the experiments: A. An electrode based on SnO2 on glass, having a surface of 3 cm2.

B. An electrode based on Au on glass, having a Bisubstrate layer and a surface of 3 cm2.

As dark electrodes were used in the experiments: C. Pt-gauze, zig-zag folded, total surface 22.5 cm2.

D. Pt-wire, rolled-up, total surface 15 cm2.

E. Carbon-felt, zig-zag folded, total surface 22.5 cm2.

The experiments were carried out using a 900 W Xenon-lamp combined with neutr: density filters and colour filters. The intensity of incident light as given in the Tables is such that 10% represents normal daylight intensity at the appropriate wave length distribution.

It should be noted that the reproducibility of the performance of the cell at very low Vdl-values is not too good, due to surface effects of the electrodes which are very difficult to avoid. This occurred mainly, however, when the known photogalvanically active compound 3,7-diamino-phenothiazine was used as a reference compound at low light intensities.

EXAMPLE 5 The photogalvanic activity of 3,7-bis (4-methyl-1-piperazinyl) phenothiazonium dichloride (MPPC) was measured in the cell described hereinabove. The concentration of MPPC was 2.10-2 mol/1 , the solvent being water. The light electrode used was A and the dark electrode C. The concentration of Fe(lI)S04 was 2.5.10-2 mol/ I and the concentration of fFe(lll)}2 (SO4)3 was 5. 10-3 mol/ I. The pH of the solution amounted to 2.5. This experiment was carried out in the absence of an added complexing agent.

The results at various light intensities (lo) are given in Table I.

TABLE I

Vdl Imax Pmax mV A 10-6.W 1 55.0 20.5 0.3 10 115.5 126 4.2 50 151.7 438 19.5 100 159.7 610 28.3 For comparative purposes the photogalvanic activity of the known photogalvanically active compound 3,7-diaminophenothiazine was measured in the form of the corresponding phenothiazonium dichloride (PTC) in the same cell, using the same electrodes (A, C) the same concentrations Fe (II) and Fe (III) at a pH 2.6.Since the experiment was carried out in water as the solvent, the maximum concentration of PTC which was obtainable was used: 6.10-5 mol/i .Again, the experiment was performed in the absence of an added complexing agent. The results are given in Table II.

TABLE II

Io Vdl Imax Pmax % mV A 10-4.W 1 0.5 0.3 8.10' 10 9.1 4.4 2.10-2 50 34.5 27 4.10-1 100 37.7 40 6.1O It will be clear from the values of Pmax recorded in Table land Table II that the performance of MPPC is several orders of magnitude better than that of PTC, thus illustrating the importance of the structural-features of the compounds according to the present invention.

EXAMPLE 6 The influence of the pH on the performance of MPPC was measured by carrying out experiments at various pH values. The experiments were carried out with an identical solution to that used in the experiments described in Example 5 but using a different but practically similar cell. The results are collated in Table III from which it appears that the pH of the photogalvanically active solution has a considerable impact on the performance of the cell. The results clearly indicate that for MPPC an increased acidity leads to decreased performance.

TABLE Ill

o = 10 Io = 50 Vdl Imax Pmax Vdl imax Pmax pH mV CLA 10-6.W mV A 10-6.W 2.8 134.2 266 10.4 169.4 780 38.3 2.5 123.6 280 10.0 162.4 800 37.7 1.9 108.6 252 7.9 145.2 720 30.3 1.7 97.7 262 7.4 134.0 720 28.0 1.2 80.1 268 7.0 116.1 71Q 24.0 EXAMPLE 7 The influence of the presence of a complexing agent on MPPC was checked by carrying out two experiments using the same concentrations of MPPC (8.10-4 mol/ I), Fe (Il)-sulphate (2.5 x 10-2 mol/ I) and Fe (III)-sulphate (6.10-4 mol/ I) at a pH of 1.8, with and without the presence of NaF as the complexing agent (when used: in a concentration of 6. 10-3 mol/l). As light-electrode the electrode B was used and D was used as the dark electrode. The results are tabulated in Table IV.

TABLE IV

Vdl imax Pmax NaF % mV CLA 10',W - 1 24.5 9.6 6.10-2 + 1 86.0 34 8.10 - 10 82.6 50 1.1 + 10 117.2 72 2.2 - 50 123.6 92 3.0 + 50 132.9 139 4.8 - 100 135.3 134 4.7 + 100 137.9 192 6.9 The experiments described in this Example were repeated using a higher concentration of MPPC: 10-2 mol/ I, instead of 8.10-4 mol/ I, at a pH of 2.0 under otherwise similar conditions. The results have been collected in Table V.

TABLE V

10 Vdl max Pmax NaF % mV A 10-6.W - 1 42.7 20 0.2 + 1 52.1 44 0.6 - 10 103.0 70 2.1 + 10 84.7 109 2.7 - 50 135.3 175 6.9 + 50 101.1 206 6.0 - 100 143.3 256 10.6 + 100 106.4 282 8.7 Just to illustrate the influence of the complexing agent sodium fluoride on the known photogalvanically active compound 3.7-diamino phenothlazine, the experiment described hereinbefore was repeated using 3.7-diamino phenothiazine, 6.10-5 mol/l as the light-sensitive compound at a pH of 1.7 under otherwise similar conditions. The results are given in Table Vl.

TABLE VI

Io Vdl Imax Pmax NaF % mV A 10-6.W - 1 1.6 0.7 3.10-4 + 1 63.3 10.8 2.10-1 - 10 18.3 8.7 4.10-2 + I 10 91.3 20 5.10 - 50 37.4 28 3.10-1 + 50 100.3 25 6.101 - 100 40-0 37 4.10-5 + 100 102.4 23 6.10-1 From the result given in Tables IV, V and VI it will be clear that sodium fluoride has a beneficial effect on the power drawn from the cell when MPPC is the light-sensitive compound applled.The effect, however, becomes less pronounced when a higher concentration of MPPC is used. A larger effect is observed using 3,7-diamino-phenothiazine as the light-sensitive compound, which, however, has a markedly lower solubility in water.

EXAMPLE 8 The influence of the ratio lower valance ion/higher valence ion in the Fe(II)/Fe(III) redox couple was checked by carrying out a number of experiments at different concentrations of Fe(III). The electrodes A and E were used. The concentration of MPPC was 10-2 mol/ I, that of Fe (li) 2.5.10-2 and the pH set at 1.9. All experiments were carried out under otherwise similar conditions. From the results, tabulated in Table VII it appears that for MPPC as the light-sensitive compound. an increasing concentration of Fe(III) leads to an optimum Pmax at relative low l0-values and a slowly increasing Pmax at rather high I0-values. It shoulds be noted that the experiments as described in this Example were carried out in the absence of a complexing agent.

TABLE VII

Fe(III).10-4 1.6 4.1 6.2 25 43 Io Vdl Imax Pmax Vdl Imax Pmax Vdl Imax Pmax Vdl Imax Pmax Vdl Imax Pmax % mV A 10-5.W mV A 10-5.W mV A 10-5.W mV A 10-5.W mV A 10-5.W 1 83.8 61 1.5 91.5 74 2.0 96.2 80 2.3 79.0 59 1.4 64.5 53 1.0 10 119.4 130 4.7 134.8 214 8.6 141.6 292 12.4 133.3 275 11.0 126.6 270 10.3 50 137.3 256 10.5 158.9 418 19.9 167.9 570 28.6 170.0 680 34.7 165.6 - 100 144.5 320 13.9 166.8 500 25.0 175.8 670 35.8 180.1 820 44.3 175.4 920 43.4 EXAMPLE 9 The photogalvanic activity of 3,7-bis (4-methyl-i -piperazinyl) phenoselenazine was measured in the way as indicated in Example 5. The concentration of the light-active compound was 2.9 x 10-3 mol/ I, the concentrations Fe (II) and Fe (III) were 2.5 x 10-2 mol/1 and 1.2 x 10-3 mol/ I, respectively.

The experiment was carried out using the electrodes A and C at a pH of 1.7. The results are given in Table VI II.

TABLE VIII

Io Vdl Imax Pmax mV 'LA 106.W 1 47.7 6 0.1 10 106.1 33 1.2 50 146.9 1 106 5.1 100 157.5 156 8.1 EXAMPLE 10 The photogalvanic activity of 3,7-bis (morpholino) phenothiazine was measured in an H-type cell using Pt-electrodes. The concentration of the light-active compound was 2. 10-5 mol/ I, the concentration Fe (II) and Fe (III) were 2.5 x 10-2 mol/l and 4. 10-4 mol/1, respectively.The experiment was carried out using a Pt-foil as light electrode (15 x 15 mm) and a rolled Pt-wire as dark electrode (15 x 100 mm) pH of 1.9. The results are given in Table IX.

TABLE IX

Io Vdl imax Pmax mV A 10-6.W 10 45.2 2.6 50 87.2 7.5 0.2 100 100.4 9.9 0.3 EXAMPLE 11 The photogalvanic activity of the dichloride of N,N,N',N'-tetrakis (3-dimethylaminopropyl) phenothiazine - 3,7-diamine was measured in the way as indicated in Example 5. The concentrations of the light-active compound was 10-4 mol/ I, the concentrations of Fe(ll) and Fe(III) were 2.5 x 10-2 mol/ I and 1.2 x 10-3 mol/ I, respectively. The experiments were carried out using the electrodes A and C at a pH of 1.1 The results are given in Table X.

TABLE X

Io Vdl Imax Pmax mV 'LA 106.W 1 3.1 2 < 4).1 10 18.6 14 0.1 50 42.4 43 0.6 100 45.9 57 1 0.8

Claims (22)

1. Compositions for use in photogalvanic cells which comprise as light-sensitive compounds heterocyclic compounds according to the general formula

wherein n is O or 1; X represents a moiety NR3, 0, S, SO2 Se or CR3R4 wherein R3 and R4 which may be the same or different each represent an alkyl group having up to 6 carbon atoms which may contain one or more nitrogen moieties or a heterocyclic ring structure having up to three nitrogen and/or oxygen atoms in the ring; at least one of R1 and R2 represents a N-containing alkyl group, and the other, if any, represents a hydrogen atom or a (N-containing) lower alkyl group or R' and R2 together with the nitrogen moiety to which they are attached form a ring-structure

080 which may contain up to two nitrogen and/or oxygen moieties or a group,NH, NR5, NH2, NHR5 or NR5R6 wherein R5 and R6 which may be the same or different each represent a hydrogen atom or a (Ncontaining) lower alkyl group, the total number of carbon atoms in the ring II, which may contain up to two double bonds, being of from 2 up to and including 6;; Y1, Y2 and Y3 which may be the same or different each represent a hydrogen atom, a halogen atom, a cyano, lower alkyl, lower alkoxy or carboxylate group or a group NR7R3, NHR7R3 or NR7R8R9 wherein R7 and R3 which may be the same or different each represent a hydrogen atom or a (N-containing) lower alkyl group or R7 and R3 together with the nitrogen moiety to which they are attached form a ring-structure

t3 t3 which may contain up to two nitrogen and/or oxygen moieties or a group NH, NR5 NH2, NHRSRB wherein R5 and R6 are as defined hereinbefore, the total number of carbon atoms in the ring III, which may contain up to two double bonds; being of from 2 up to and including 6, and R9 represents a hydrogen atom or a lower alkyl group; Z1, Z2, Z3 and Z4 which may be the same or different each represent a hydrogen atom, a cyano, lower alkyl, lower alkoxy or carboxylate group or a group r3 S) NHR7R8 or NR7R8R9 wherein R7, R8 and R9 are as defined hereinbefore; B represents an anion and m is a whole number matching the electroneutrality, the o-chinons as well as the corresponding dihydrochinoids.

2. Compositions according to claim 1 wherein n = 1; X represents a moiety 0, S, SO, or Se; at least one of R' and R2 represent a N-containing lower alkyl group, and the other if any, represents a hydrogen atom or a (N-containing) lower alkyl group or R1 and R2 together with the nitrogen moiety to which they are attached form a ring structure II which may contain up to two nitrogen and/or oxygen moiet7es 3 or a group NH, NR5, NH2, NHRs or NR5R6 wherein R5 and R6 which may be the same or different each represent a hydrogen atom or a lower alkyl group which may or may not contain a nitrogen atom, the total number of carbon atoms in the ring II, which may contain up to two double bonds, being 3, 4 or 5: Y1, Y2 and Y3 which may be the same or different each represent a hydrogen atom, a cyano, methyl or 0 0 lower alkoxy group or a group NR7R8, NHR7R8 or NR7R8R9 wherein R7 and R8 which may be the same or different each represent a hydrogen atom or a N-containing alkyl group or R7 and R8 together with the nitrogen atom to which they are attached form a ring-structure Ill which may contain up to two nitrogen 0 0+ 0 and/or oxygen moieties or a group NH, NR5, NH2, NHRs or NR5R6 wherein Rs and R6 which may be the same or different each represent a hydrogen atom or a lower alkyl group which may or may not contain a nitrogen atom, and R9 represents a hydrogen atom or a lower alkyl group: Z1, Z2, Z3 and Z4 which may be the same or different each represent a hydrogen atom, a halogen atom, a cyano, methyl or lower 0+ alkoxy group or a group NR7R3, NHR7R8 or NHR7R8R9 wherein R7, R8 and R9 are as defined hereinbefore: B represents a halide, (hydro)sulphate, (hydro)phosphate, nitrate, fluoroborate or perchlorate and m is an integer matching the electroneutrality, the o-chinons and the corresponding dihydrochinoids.

3. Compositions according to claim 2, wherein n = 1; X represents an oxygen, sulphur or selenium moiety; R' and R2 both represent a N-containing alkyl group having up to 6 carbon atoms or R' and R2 together with the nitrogen moiety to which they are attached form a ring-structure II which also contains one or two oxygen and/or nitrogen moieties or a group NR5 wherein R5 represents a hydrogen atom or a lower alkyl group, especially a methyl group, the total number of carbon atoms in the ring II, which may contain up to two double bonds, being 3 or 4;; Y1, Y2 and Y3 which may be the same or different each represent a hydrogen or halogen atom or a group NS7R8 or NHR7R8 wherein R7 and R8 both represent a N-containing alkyl group having up to 6 carbon atoms or R7 and R3 together with the nitrogen moiety to which they are attached form a ring-structure Ill which may contain up to two nitrogen and/or oxygen atoms or a group NR5 wherein R5 represents a hydrogen atom or a lower alkyl group, especially a methyl group, the total number of carbon atoms in the ring III being 3 or 4, Z', Z3 or Z4 which may be the same or different represent a hydrogen or halogen atom and Z2 represents a hydrogen or halogen atom, or preferably a group NR7R8 or NHR7R8 wherein R7 and R3 are as defined hereinbefore; B represents a halide, sulphate, fluoroborate or perchlorate and m is an integer matching the electroneutrality.

4. Compounds according to the general formula I with the exception of 3,7-bis (4-methyl-i - piperazinyl) phenothiazonium bromide.

5. Compounds according to claim 4 wherein the substituents having the meaning as defined in claim 2.

6. Compounds according to claim 5, wherein the substituents have the meaning as defined in claim 3.

7. 3,7-bis (4-methyl-I -piperazinyl) phenothiazonium dichloride.

8. 3,7-bis (4-methyl-1-piperazinyl) phenoselenazonium dichloride.

9. 3,7-bis (morpholino) phenothiazonium dichloride.

10. The dichloride of N,N,N1,N'-tetrnkis (3-dimethylaminopropyl)phenothiazine-3,7-diamine.

1 1. Process for the preparation of heterocyclic compounds according to any one of the claims 410 which comprises the oxidation of the appropriate carbazole, phenazine, phenoxazine, phenothiazine, phenothiazine 5,5-dioxide, phenoselenazine or acridine with bromine or Fe,(lIl)-chloride in the presence of compounds containing the nitrogen-containing group(s) to be introduced into the starting material.

12. Process according to claim 1 which comprises the oxidation of the starting material with Fe (111)-chloride in the presence of a cyclic nitrogen moiety to be introduced into the starting material.

13. Photogalvanically active compositions according to any one of claims 1-3 which comprise water as the solvent.

14. Photogalvanically active compositions according to any one of claims 1-3 and 13 which comprise the presence of at least one complexing agent such as fluorides, phosphates, salts of dibasic organic acids and amino acids and salts thereof.

1 5. Photogalvanically active compositions according to claim 14 which comprises the presence of sodium fluoride and/or sodium phosphate as complexing agent.

16. Photogalvanically active compositions according to claim 14 or 15 which comprise the use of complexing agents in a molar concentration of from 0.1 to 50 times the concentration of the highervalence partner (oxidator) employed.

17. Photogalvanically active compositions according to any one of claims 1-3 and 1316, substantially as hereinbefore described with reference to the non-comparative parts of the Examples 5-11.

18. Photogalvanic cells which comprise at least one heterocyclic compound according to any one of claims 1-3 as the light-sensitive compound, at least one redox-couple and a set of electrodes and optionally a complexing agent.

19. Photogalvanic cells according to claim 18 which comprise an electrode based on platinum, gold, carbon, titanium dioxide or SnO2 as light-electrode and platinum, carbon or indium-tinoxide as dark electrode.

20. Photogalvanic cells according to claim 19, which comprise the use of a dark electrode having a surface area of at least 5 times that of the light-electrode.

21. Photogalvanic cells according to any one of claims 1820, substantially as hereinbefore described with reference to the Examples 511.

22. Photogalvanic processes which comprise the use of a photogalvanic cell according to any one of claims 1821 containing a photogalvanically active composition according to any one of claims 13.