JPH0337177B2 - - Google Patents

Description

[Detailed description of the invention]

1. Field of Industrial Application The present invention relates to a photoreceptor, such as an electrophotographic photoreceptor, having a photosensitive layer comprising a carrier generation phase and a carrier transport phase. 2. Prior Art Conventionally, inorganic photoreceptors having a photosensitive layer containing an inorganic photoconductive substance such as selenium, zinc oxide, or cadmium sulfide as a main component have been widely used as electrophotographic photoreceptors. However, such inorganic photoreceptors do not necessarily satisfy the characteristics required for electrophotographic photoreceptors, such as sensitivity, thermal stability, moisture resistance, and durability. For example, selenium crystallizes due to heat, the adhesion of dirt such as fingerprints, etc., and therefore its properties as an electrophotographic photoreceptor tend to deteriorate.
Further, when cadmium sulfide is used, there are problems in moisture resistance and durability, and when zinc oxide is used, there are problems in durability. Furthermore, selenium and cadmium sulfide have significant restrictions in manufacturing and handling. In order to overcome the above-mentioned drawbacks of inorganic photoreceptors, the use of various organic photoconductive substances as materials for the photosensitive layer of electrophotographic photoreceptors has been actively developed and researched in recent years. For example, in Japanese Patent Publication No. 50-10496, poly
An organic photoreceptor having a photosensitive layer containing N-vinylcarbazole and 2,4,7-trinitro-9 fluorenone is described. However, this photoreceptor is not necessarily satisfactory in sensitivity and durability. In order to improve these drawbacks, attempts have been made to develop organic photoreceptors with high sensitivity and durability by assigning the carrier generation function and carrier transport function to different substances in the photosensitive layer. ing. In such so-called function-separated type electrophotographic photoreceptors, it is possible to select substances that exhibit each function from a wide range of materials, so it is relatively easy to produce electrophotographic photoreceptors with arbitrary characteristics. It is possible to do so. Many substances have been proposed as carrier generating substances that are effective for such functionally separated electrophotographic photoreceptors. An example of using an inorganic substance is amorphous selenium, as described in Japanese Patent Publication No. 43-16198. Although this is combined with an organic carrier transport substance, the carrier generation layer made of amorphous selenium has the disadvantage that, as mentioned above, it crystallizes due to heat or the like and its properties deteriorate. In addition, many electrophotographic photoreceptors using organic dyes or organic pigments as carrier generating substances have been proposed. Akira
It is already known from JP-A-55-22834, JP-A-54-79632, JP-A-56-116040, etc.
However, electrophotographic photoreceptors using these bisazo compounds are not necessarily satisfactory in terms of sensitivity, residual potential, or even stability during repeated use, and the range of selection of materials to be used as carrier transport materials is limited. However, the electrophotographic photoreceptor does not fully satisfy the wide range of demands in the electrophotographic process that electrophotographic photoreceptors undergo. Furthermore, although known bisazo compounds exhibit relatively good sensitivity in the short or medium wavelength range, they lack sensitivity in the long wavelength range, and for example, when a tungsten lamp is used as a light source, the long wavelength component is wasted. Further, long wavelength light such as a semiconductor laser cannot be used as a light source. Therefore, the usable wavelength range is limited, and it cannot be used for many purposes. Additionally, in general, in photoreceptors, a carrier transport material that is effective against a specific carrier-generating substance is not necessarily effective against other carrier-generating substances, and It cannot be said that a carrier generating substance that is effective against other carrier transport substances is also effective against other carrier transport substances. If the combination of these two materials is inappropriate, not only will the electrophotographic sensitivity become low, but also the discharge efficiency will be poor especially at low electric fields, so the so-called residual potential will increase, and in the worst case, repeated use will cause damage. Potential accumulates on the surface, making it practically unusable for electrophotographic purposes. In this way, it is thought that there is no lawful means of selecting a suitable combination of the constituent substances of the carrier generation phase and the constituent substances of the carrier transport phase, and an advantageous combination is determined practically from among many substance groups. There is a need to. 3. Purpose of the invention The purpose of the present invention is to contain a specific carrier-generating substance, be stable against heat and light, have high carrier-generating efficiency, and have excellent photoconductivity even in a wide wavelength range. The object of the present invention is to provide a photoreceptor whose potential history state is maintained stably even during repeated use by combination with a specific carrier transport substance, and which can always form good visible images. 4 Structure of the invention and its effects That is, the present invention provides a photoreceptor having a photosensitive layer consisting of a carrier generation phase and a carrier transport phase,
The photoreceptor is characterized in that the carrier generation phase contains a bisazo compound represented by the following general formula [], and the carrier transport phase contains a pyrazoline compound represented by the following general formula []. General formula []: (However, in this general formula, A is

【formula】

【formula】

[expression] or

[Formula], Z: a group of atoms necessary to constitute a substituted or unsubstituted aromatic carbocycle or a substituted or unsubstituted aromatic heterocycle, Y: a hydrogen atom, a hydroxyl group, a carboxyl group, or an ester group thereof , sulfo group, substituted or unsubstituted carbamoyl group, or substituted or unsubstituted sulfamoyl group, R ¹ : hydrogen atom, substituted or unsubstituted alkyl group, substituted or unsubstituted amino group, substituted or unsubstituted carbamoyl group , carboxyl group or its ester group, or cyano group, _Ar : substituted or unsubstituted aryl group, R ² : substituted or unsubstituted alkyl group, substituted or unsubstituted aralkyl group, or substituted or unsubstituted aryl group represents. ) General formula []: [However, in this general formula, l is 0 or 1, R ³ , R ⁴ and R ⁵ are substituted or unsubstituted aryl groups, R ⁶ and R ⁷ are hydrogen atoms, and have 1 to 4 carbon atoms.
an alkyl group, or a substituted or unsubstituted aryl group or aralkyl group (However, R ⁶ and R ⁷ are not both hydrogen atoms, and when l is 0, R ⁶ is not a hydrogen atom.) represents. ] In the present invention, the above-mentioned "phase" includes not only the case where the material forms a so-called layer, but also the case where the constituent materials form phases in which they are in contact with each other. According to the present invention, as is clear from the description of the examples to be described later, it is stable against heat and light, and has excellent characteristics such as charge retention, sensitivity, and residual potential, and can be used repeatedly. In some cases, it is possible to provide a photosensitive couple with little fatigue change and high durability. In particular, in the present invention, the bisazo compound represented by the above general formula [] has an excellent carrier generation ability, and this is combined with the carrier transport material of the above general formula [] to form a photosensitive layer into a functionally separated type. By adopting this structure, it is possible to obtain a photoreceptor with even more excellent characteristics. Among the bisazo compounds of the above general formula [], carbazole group-containing bisazo compounds represented by the following general formula ['] are particularly effective. General formula [I′]: (However, R ¹⁰ and R ¹¹ are alkyl groups, alkoxy groups, or aryl groups, R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ , and R ¹⁷ are hydrogen atoms,
These are a halogen atom, an alkyl group, an alkoxy group, an amino group, a hydroxyl group, and an aryl group. ) This bisazo compound of general formula ['] is thought to have a carbazole group in the molecule that contributes to the sensitizing effect, giving it excellent sensitivity especially in the long wavelength range, and the carbamoyl group in the molecule contributing to the sensitizing effect. In combination with other parts, it acts effectively as a coupler, exhibits good sensitivity characteristics over a wide wavelength range, and exhibits excellent characteristics as a photoreceptor for semiconductor lasers. Furthermore, the pyrazoline compound represented by the general formula [] according to the present invention has excellent compatibility with various polymeric binders, and does not cause turbidity or opacity even when the amount of the compound with respect to the polymeric binder is increased. Therefore, the polymer binder can be mixed in a very wide range, and a photoreceptor having favorable charge transport performance and physical properties can be produced. Since the compatibility is excellent, the charge transport phase is uniform and stable, and as a result, a photoreceptor can be obtained that has no sensitivity, no charging characteristics, and no fog, and can form high-density, clear images. In addition, especially when used in repeated transfer type electrophotography, it is possible to achieve the effect that fatigue deterioration does not occur.
The pyrazoline compound used as the charge transporting substance of the present invention has the role of receiving the charge generated by the charge-generating substance and transporting it. Therefore, in the pyrazoline compound of the present invention, at least one aryl group has an electron-donating group such as an amino group, a dialkylamine group, a diarylamino group, a dialkylamino group, or an alkoxy group (having a negative Hammett's sigma (σ) value). It is preferable that the substituent is substituted with a substituent such as The reason for this is presumed to be that these electron-donating groups have the effect of lowering the ionization potential of the compound and making it easier to receive charge injection from a charge-generating substance. Among the pyrazoline compounds represented by the general formula [], those represented by the following general formula [a] are preferred. General formula [a]: [In this general formula, l represents 0 or 1, R ¹⁸ ,
R ¹⁹ and R ²⁰ are a hydrogen atom, an amino group, a dialkylamino group, a diarylamino group, a dialkylamino group, an alkoxy group, and R ⁶ and R ⁷ are the same as those described above. ] Specific examples of the bisazo compound represented by the above general formula [ ] that are effective in the present invention include those represented by the following structural formula; is not limited. Examples of the pyrazoline compound useful in the present invention represented by the general formula [] include those having the following structural formula. Bisazo compounds as mentioned above, such as the above (
The bisazo compound represented by -1) can be synthesized, for example, by the method shown in the following synthesis example. First, 2,7-dinitro-9-fluorenone and malonic acid nitrile were mixed using a known method (for example, J.Org.
When the compound (2,7-dinitro-9-dicyanomethylidenefluorene) obtained by dehydration condensation according to Chem., Vol. 30, p. 644 (published in 1965) is reduced with tin and hydrochloric acid, 2,7-diamino -9-dicyanomethylidenefluorene dihydrochloride was obtained. 3.30g (0.01mol) of it was added to 100% of hydrochloric acid.
ml, and heated the dispersion to a temperature of 5 mL while stirring.
Cool to 20 °C and add 1.4 g of sodium nitrite to it.
An aqueous solution dissolved in 1 ml of water was removed and added.
After the dropwise addition was completed, stirring was continued under cooling for an additional hour, and then filtration was performed. 10 g of ammonium hexafluorophosphate was added to the obtained filtrate, and the resulting crystals were collected by filtration. Phosphate was obtained. These crystals were dissolved in 200 ml of N,N-dimethylformamide to obtain a dropwise solution for the next coupling reaction. Next, 5.27 g (0.02 mol) of 2-hydroxy-3-naphthoic acid anilide (naphthol AS) was added to N,N-
The solution was dissolved in 200 ml of dimethylformamide, and 5.5 g of triethanolamine was added thereto. The solution was cooled to a temperature of 5° C., and the above-described solution was added dropwise thereto while stirring vigorously. After the dropwise addition was completed, the mixture was stirred for 1 hour under cooling, and further stirred for 2 hours at room temperature, and then the resulting crystals were collected by filtration. This result is 1
twice with N,N-dimethylformamide of 1
After washing twice with acetone and drying, 6.70 g (yield: 83.0%) of a blue compound was obtained. This blue compound was targeted because absorption due to the C=O bond of the amide was observed at ν = 1680 cm ^-1 in its infrared absorption spectrum, and the actual measured values of elemental analysis showed high consistency. It was confirmed to be compound (-1). The results of elemental analysis (chemical formula is C ₅₀ H ₃₀ N ₈ O ₄ ) were as follows. Element C H N Actual value (%) 74.61 3.70 13.67 Theoretical value (%) 74.43 3.74 13.89 For constituting the photosensitive layer of the photoreceptor of the present invention, for example, an electrophotographic photoreceptor, using the bisazo compound represented by the above general formula [] For this purpose, a layer in which the bisazo compound is dispersed in a binder may be provided on a conductive support. Alternatively, the bisazo compound may be used as a carrier-generating substance and combined with a carrier-transporting substance of the general formula [] having a carrier-transporting ability to provide a so-called functionally separated photosensitive layer of laminated or dispersed type. In the composition of the photosensitive layer, not only one type of bisazo compound represented by the above general formula [] but also a combination of two or more types can be used, and it can also be used in combination with other bisazo compounds or other carrier-generating substances. When the electrophotographic photoreceptor is of a functionally separated type, it is usually constructed as shown in FIGS. 1 to 6. 1 and 3, a carrier generation layer 2 containing the above-mentioned bisazo compound as a main component and a carrier transport layer 3 containing the above-mentioned pyrazoline compound as a main component are laminated on a conductive support 1. This is a structure in which a photosensitive layer 4 made of a body is provided. 2 and 4 have a structure in which an intermediate layer 5 is provided between the conductive support 1 and the photosensitive layer 4 in the structure shown in FIGS. 1 and 3, respectively. In the case shown in FIG. 5, a photosensitive layer 4 comprising a carrier generating substance 7 made of the above-mentioned bisazo compound dispersed in a layer 6 containing the above-mentioned pyrazoline compound (carrier transport substance) as a main component is attached to a conductive support. 1, the structure shown in FIG. 6 is a structure in which a photosensitive layer 4 similar to that shown in FIG. 5 is provided on the conductive support 1 via an intermediate layer 5. In the case of forming a photosensitive layer having a two-layer structure, the carrier generation layer 2 can be provided by the following method. (a) A method of applying a solution prepared by dissolving the above-mentioned bisazo compound in a suitable solvent, or a solution obtained by adding a binder to the solution and mixing and dissolving it. (b) The bisazo compound described above is made into fine particles in a dispersion medium using a ball mill, a homomixer, etc.
A method in which a binder is added as necessary and a dispersion obtained by mixing and dispersing is applied. When particles are dispersed under the action of ultrasound in these methods, uniform dispersion is possible. The solvent or dispersion medium used for forming the carrier generation layer includes n-butylamine, diethylamine, ethylenediamine, isopropanolamine, triethanolamine, triethylenediamine, N,N-dimethylformamide, acetone,
Methyl ethyl ketone, cyclohexanone, benzene, toluene, xylene, chloroform, 1,2
- Dichloroethane, dichloromethane, tetrahydrofuran, dioxane, methanol, ethanol, isopropanol, ethyl acetate, butyl acetate, dimethyl sulfoxide and the like. When a binder is used to form a carrier generation layer or a carrier transport layer, any binder can be used, but in particular an electrically insulating film-forming polymer that is hydrophobic and has a high dielectric constant. is preferred. Examples of such polymers include, but are not limited to, the following: (a) Polycarbonate (b) Polyester (c) Methacrylic resin (d) Acrylic resin (e) Polyvinyl chloride (f) Polyvinylidene chloride (g) Polystyrene (h) Polyvinyl acetate (i) Styrene-butadiene copolymer (j ) Vinylidene chloride-acrylonitrile copolymer (k) Vinyl chloride-vinyl acetate copolymer (l) Vinyl chloride-vinyl acetate-maleic anhydride copolymer (m) Silicone resin (n) Silicone-alkyd resin (o) Phenol -Formaldehyde resin (p) Styrene-alkyd resin (q) Poly-N-vinylcarbazole (r) Polyvinyl butyral These binders can be used alone or in a mixture of two or more. The ratio of the carrier generating substance to the binder is preferably 0 to 100% by weight (especially 0 to 10% by weight), and the proportion of the carrier transporting substance is preferably 10 to 500 parts by weight. The thickness of the carrier generation layer 2 thus formed is preferably 0.01 to 20 μm, more preferably 0.05 to 5 μm. The thickness of the carrier transport layer is between 2 and 100 μm, preferably between 5 and 30 μm. In addition, when the above-mentioned bisazo compound is dispersed to form a photosensitive layer or a carrier generation layer, the bisazo compound is in the form of powder with an average particle size of 5 μm or less, preferably 2 μm or less, and more preferably 1 μm or less. It is preferable to That is, if the particle size is too large, dispersion in the layer will be poor, and some of the particles will protrude from the surface, resulting in poor surface smoothness. Toner particles tend to adhere to the toner, causing a toner filming phenomenon. Long wavelength light (~
800 nm), the surface charge is neutralized by the generation of thermally excited carriers in the carrier-generating substance, and it is thought that this neutralization effect is greater when the particle size of the carrier-generating substance is large. Therefore, high resistance and high sensitivity can only be achieved by reducing the particle size. However, if the above particle size is too small, it tends to aggregate, which increases the resistance of the layer, increases crystal defects and reduces sensitivity and repeatability, or there is a limit to miniaturization. It is desirable that the lower limit of the diameter is 0.01 μm. In addition, in the above carrier generation layer (or phase),
It is generally said that amines in an amount less than 20 times the number of moles (preferably a small amount) relative to the carrier generating substance are effective for improving sensitivity (see JP-A-52-55643), but the amount is too large. Many amines have strong irritating odors, so using large amounts of amines may worsen the environmental conditions during application, increase the drying time after application, and cause the surface to become sticky even after drying. Resulting in. However, if the amine is specified to be 20 times or less (preferably 10 times or less, especially 5 times or less) as large as the carrier generating substance, the charge generating substance will not be substantially dissolved by the amine during coating formation of the carrier generating layer. (that is, the amine does not act as a solvent), and can be dispersed in the coating liquid. As a result, it becomes possible to apply the coating in a dispersed state, improving the crystallinity of the coating layer, and
There is no change in the absorption spectrum, and photosensitivity improves. Furthermore, dark decay and reduction in acceptance potential during repeated use, which are generally caused by using an azo compound as a carrier generating substance, are effectively prevented by the above-mentioned amine content range. Furthermore, since the amount of amine is small, the drying time after application is shortened and the surface becomes non-sticky.
It is also advantageous in terms of environmental protection during application. Furthermore, depending on the above amine content, it is possible to improve various properties such as photosensitivity by adding an amine. This is noticeable if you have. Furthermore, due to the above content of amine, the amine is effectively adsorbed to the acceptor site in the carrier generation layer, reducing the acceptor concentration and increasing the electrical resistance of the carrier generation layer, thereby increasing the acceptance potential. It is thought that this can reduce dark decay. The above-mentioned amines added in small amounts to the carrier generation layer include monoethanolamine, n-butylamine,
It may consist of primary amines such as ethylenediamine, secondary amines such as diethanolamine and diethylamine, tertiary amines such as triethanolamine and triethylamine, and heterocyclic amines such as pyridine and piperidine. Furthermore, the carrier generating layer may contain one or more electron-accepting substances for the purpose of improving sensitivity, reducing residual potential or fatigue during repeated use, and the like. Examples of electron-accepting substances that can be used here include succinic anhydride,
Maleic anhydride, dibromaleic anhydride, phthalic anhydride, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, 3-nitrophthalic anhydride, 4
-Nitrophthalic anhydride, pyromellitic anhydride, mellitic anhydride, tetracyanoethylene, tetracyanoquinodimethane, o-dinitrobenzene, m-
Dinitrobenzene, 1,3,5-trinitrobenzene, paranitrobenzonitrile, picryl chloride, quinone chlorimide, chloranil, brumanil, dichlorodicyanoparabenzoquinone, anthraquinone, dinitroanthraquinone, 2,7
-dinitrofluorenone, 2,4,7-trinitrofluorenone, 2,4,5,7-tetranitrofluorenone, 9-fluorenylidene [dicyanomethylenemalonodinitrile], polynitro-9-
Fluorenylidene-[dicyanomethylenemalonodinitrile], picric acid, o-nitrobenzoic acid,
p-nitrobenzoic acid, 3,5-dinitrobenzoic acid, pentafluorobenzoic acid, 5-nitrosalicylic acid, 3,5-dinitrosalicylic acid, phthalic acid,
Examples include mellitic acid and other compounds with high electron affinity. Further, the addition ratio of the electron-accepting substance is carrier-generating substance: electron-accepting substance = 100:0.01 to 200, preferably 100:0.1 to
It is 100. Note that the support 1 on which the above-mentioned photosensitive layer is to be provided
metal plate, metal drum or conductive polymer,
A thin conductive layer made of a conductive compound such as indium oxide or a metal such as aluminum, palladium, or gold is applied to a substrate such as paper or plastic film by coating, vapor deposition, lamination, or the like. As the intermediate layer which functions as an adhesive layer or a barrier layer, a material made of a polymer as described above as a binder, an organic polymer substance such as polyvinyl alcohol, ethyl cellulose, or carboxymethyl cellulose, or aluminum oxide is used. . 5 Examples Hereinafter, the present invention will be described in more detail with reference to specific examples and comparative examples. A thin layer of vinyl chloride-vinyl acetate-maleic anhydride copolymer "Eslec MF-10" (manufactured by Sekisui Chemical Co., Ltd.) was placed on a conductive support made of polyester film laminated with aluminum foil.
An intermediate layer of 0.05 μm was formed. Next, each of the carrier-generating substances and the binder having the predetermined particle size shown in FIG. ) was coated and dried on the intermediate layer so that the film thickness after drying was 0.5 μm to form a carrier generation layer. Furthermore, the seventh
A solution prepared by dissolving each of the carrier transport substances and binder shown in the figure in 53 ml of 1,2-dichloroethane was coated and dried to a film thickness of 12 μm after drying to form a carrier transport layer. was created. The electrophotographic photoreceptor thus obtained was mounted on an electrostatic paper tester "SP-428 model" (manufactured by Kawaguchi Denki Seisakusho).
The following characteristic tests were conducted. In other words, the charger -
After applying a voltage of 6 KV and charging the photosensitive layer by corona discharge for 5 seconds, it was left to stand for 5 seconds (the potential at this time is V _I ), and then the illuminance on the surface of the photosensitive layer was 35 lux. Irradiate light from a tungsten lamp to reduce the surface potential of the photosensitive layer by half.
The exposure amount required to attenuate the light by half, that is, the half-reduced exposure amount E1/2 was determined. In addition, the acceptance potential when charged by the corona discharge was measured at the initial stage of _VA and after 10,000 copies. In addition, the attenuation rate (V _A − V _I )/V _I ×100 (%) and the exposure amount E ⁵⁰⁰ ₅₀ required to further attenuate the initial potential V _I from −500 (V) to −50 (V) (lux・sec) was measured. Furthermore, the sensitivity of the semiconductor laser (780 nm) was also shown (◎ mark is extremely good, ○ mark is good, △ is slightly poor, × mark is poor, - indicates that no experiment was conducted.) The results are summarized. It is shown in Figure 7. However, the carrier-generating substance and the carrier-transporting substance are indicated by the numbers of the structural formulas exemplified above. According to the results, it can be seen that the samples of Examples (No. 1 to No. 14) based on the present invention all exhibit considerably better electrophotographic characteristics than Comparative Examples No. 1 to No. 5. FIG. 8 shows a sensitivity curve a when a photoreceptor is constructed as in the same example using the bisazo compound according to the present invention (Example No. 1 in FIG. 7) as a carrier generating substance. It can be seen that the photoreceptor according to the present invention exhibits excellent sensitivity even in a wide wavelength range, particularly in a long wavelength range such as a semiconductor laser range.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIGS. 1, 2, 3, 4, 5, and 6 are cross sections of a portion of each example of an electrophotographic photoreceptor. FIG. 7 is a graph showing a comparison of changes in characteristics depending on the composition of each electrophotographic photoreceptor, and FIG. 8 is a graph showing photosensitivity due to carrier-generating substances. In addition, in the reference numerals shown in the drawings, 2... carrier generation layer, 3... carrier transport layer, 4... photosensitive layer, 6... mixed layer of carrier generation substance and carrier transport substance.

Claims (1)

[Scope of Claims] 1. A photoreceptor having a photosensitive layer consisting of a carrier generation phase and a carrier transport phase, wherein the carrier generation phase contains a bisazo compound represented by the following general formula [], and the carrier transport phase comprises a bisazo compound represented by the following general formula []. A photoreceptor characterized by containing a pyrazoline compound represented by the general formula []. General formula []: (However, in this general formula, A is [Formula] [Formula] [Formula] or [Formula], Z: constitutes a substituted or unsubstituted aromatic carbocycle or a substituted or unsubstituted aromatic heterocycle Atom group necessary for Y: hydrogen atom, hydroxyl group, carboxyl group, or ester group thereof, sulfo group, substituted or unsubstituted carbamoyl group, or substituted or unsubstituted sulfamoyl group, R ¹ : hydrogen atom, substituted or Unsubstituted alkyl group, substituted or unsubstituted amino group, substituted or unsubstituted carbamoyl group, carboxyl group or its ester group, or cyano group, _Ar : substituted or unsubstituted aryl group, R ² : substituted or unsubstituted Represents a substituted alkyl group, a substituted or unsubstituted aralkyl group, or a substituted or unsubstituted aryl group.) General formula []: [However, in this general formula, l is 0 or 1, R ³ , R ⁴ and R ⁵ are substituted or unsubstituted aryl groups, R ⁶ and R ⁷ are hydrogen atoms, and have 1 to 4 carbon atoms.
an alkyl group, or a substituted or unsubstituted aryl group or aralkyl group (However, R ⁶ and R ⁷ are not both hydrogen atoms, and when l is 0, R ⁶ is not a hydrogen atom.) represents. ]