DE112011105620T5 - Photorefractive composite - Google Patents

Abstract

The present invention relates to a photorefractive composite comprising a hole conductor, a nonlinear optical unit and a sensitizer, the sensitizer being C12-4Cl diperylene bisimide, and the use of the photorefractive composite with C12-4Cl diperylene bisimide in holographic techniques, in optics and Laser optics or in photovoltaic cells, organic field effect transistors and organic light emitting diodes.

Description

The present invention relates to a photorefractive composite. In particular, the present invention relates to sensitizers for photorefractive composites.

Modern technologies, such as lasers, LEDs and fiber optic communication, require and motivate the further development of new materials while exploring applicable matter-light interactions. The already achieved, considerable progress in the development of photosensitive and photoconductive materials enables the conversion of sunlight into electricity within solar cells. Also worth mentioning is the production of electro-optical devices, such as flat-panel LCDs, based on the light-modulating properties of liquid crystals. One particular type of material that interacts with light is photorefractive material. Combining the useful properties of photoconductivity and electro-optics, photorefractive materials can change their refractive index under uneven illumination with light. This specific mechanism makes them promising candidates for future applications, such as high-density holographic data storage, holographic imaging of living tissue, and 3D real-time image displays. Therefore, continuous data growth, medical diagnostics and the entertainment industry have an urgent need for innovative refractive index modulating high performance materials. In addition, photorefractive materials are indispensable for the realization of nanophotonic devices for optical information processing. But despite growing demand, insurmountable drawbacks such as high production costs and long-term production have hampered the definitive advance since Ashkin's first observation of the photorefractive phenomena in 1966 in an inorganic crystal. Nevertheless, the replacement of inorganic crystals by photosensitive and electro-optical organic materials has been a considerable success. Their advantages include cost-effective synthesis, easy modification and fast manufacturing.

While many organic photorefractive materials have been identified and potentially approached in the last 20 years, the breakthrough they are hoping for will not be forthcoming. The main reason for the lack of expected success is the inadequate photoconductivity at the desired wavelength resulting from inefficient carrier generation during illumination with light. Photoconductivity in organic materials, for example, can be achieved by doping a conductive polymer with a light absorbing molecule called a sensitizer.

In general, this type of composite contains a polymeric hole conductor, a rod-shape-like non-linear optical unit, and a sensitizer. In these DC biased mixtures, a photorefractive effect is observed when the following processes take place: The sensitizer absorbs optical radiation of a light pattern, thereby generating charge carriers in the regions of high light intensity. While the sensitizer anions remain immobile thereafter, the mobile positive charge carriers are transported by the polymer into the dark regions where they are trapped. This leads to the formation of a space charge field E _sc , which rearranges the nonlinear optical molecules and thereby causes the refractive index change Δn. This induced index modulation is phase shifted with respect to the incident light pattern. According to the reorientation of the non-linear optical units in low glass transition temperature materials, the refractive index change of the material is strongly influenced by the effect of the orientation gain.

Although the content of the sensitizer in a photorefractive composite is very low, it plays a crucial role in charge generation and, as a result, photoconductivity. It is well known that the photorefractive dynamics are strongly influenced and even limited by the photoconductivity of the photorefractive composite. A well-known and used sensitizer is [6,6] -phenyl-C61-butyric acid methyl ester (PCBM), which has been successfully used as an n-type material in organic field effect transistors, photodetectors and photovoltaic cells. In both devices, however, the photorefraction speed and photosensitivity must be improved. As a result, there is still a need for innovative sensitisers.

Therefore, the object underlying the present invention was to provide a sensitizer which can be used in photorefractive composites.

The problem is solved by a photorefractive composite comprising a hole conductor, a non-linear optical unit and a sensitizer, wherein the sensitizer is C12-4Cl diperylene bismuth according to the following formula (1):

As used herein, the term "C12-4Cl diperylene bisimide" refers to the compound of formula (1). The compound of the formula (1) is referred to as C12-4Cl diperylene bisimide or C12-4Cl diPBI. C12-4C1-Diperylenebisimide may also be prepared as 2,3,13,14-tetrachloro-6,10,17,21-tetradodecylpyranthreno [6,7,8-def: 14,15,16-d'e. According to the IUPAC nomenclature 'f': 3,4,5-d''e''f''g '': 11,12,13-d '' 'e' '' f '' 'g' ''] tetraisochinolin-5, 7,9,11,16,18,20,22 (6H, 10H, 17H, 21H) octaone.

As used herein, the term "photorefractivity" refers to the reversible change in refractive index during inhomogeneous illumination with light. Photorefractivity requires, in addition to photoconductivity, an electro-optic response.

Surprisingly, it has been found that C12-4Cl diperylene bisimide (C12-4Cl-DiPBI) provides excellent workability of photorefractive materials in the full range of visible light. The absorption of a photorefractive composite with C12-4Cl-diperylenebisimide (C12-4Cl-DiPBI) captures the full range of visible light, with peaks in the blue, green, and red regions, and is particularly advantageous since the known sensitizer [6,6] -phenyl-C61-butyric acid methyl ester (PCBM) is hardly absorbing and even monoperylenebisimide absorbs preferably only blue and green light.

Advantageously, it has been found that C12-4Cl-diperylenebisimide (C12-4Cl-DiPBI) increases the photoelectric generation efficiency over known sensitizers such as [6,6] -phenyl-C61-butyric acid methyl ester (PCBM), thereby increasing the ability to write a Hologram required time shortened by a factor of 39. Such an improvement may counteract the need for stability of the experimental set-up against environmental mechanical disturbances and even allow 3D imaging of moving objects. It is also advantageous that C12-4Cl diperylene bisimide can provide twice as high photorefractive power as PCBM at only one quarter of the sensitizer concentration.

In addition, C12-4Cl diperylene bisimide (C12-4Cl-DiPBI) provides strong visible light absorption, high fluorescence quantum yield, and excellent photostability, high electron affinity, and charge-carrier mobility. Moreover, C12-4Cl diperylene bisimide provides exceptional thermal, chemical and physical stability. In addition, C12-4Cl diperylene bisimide is highly soluble in common solvents such as toluene, tetrahydrofuran, thiophene and cyclohexanone.

The photorefractive composite can provide high gain and fast photorefractive response. Furthermore, the photorefractive composite may advantageously be resistant to high electric fields. Advantageously, the photorefractive composite exhibits no phase separation and no crystallization. Further, the glass transition temperature of the photorefractive composite is near the ambient temperature.

In a preferred embodiment, the composite comprises C12-4Cl-diperylenebisimide in an amount in the range of ≥ 0.001 wt .-% to ≤ 1 wt .-%, preferably in the range of ≥ 0.002 wt .-% to ≤ 0.5 wt. %, in particular in the range of ≥ 0.01 wt .-% to ≤ 0.348 wt .-% and more particularly in the range of ≥ 0.01 wt .-% to ≤ 0.222 wt .-% based on a total amount of the composite of 100 wt .-%.

Percent by weight, by weight or by weight are synonyms referring to the concentration of a component as the weight of the component divided by the weight of the composition and multiplied by 100. The weight percentages (wt.%) Of the components are calculated based on the total weight of the composition, unless otherwise specified.

Photorefractive composites that have a low concentration of C12-4Cl diperylene bisimide (C12-4Cl-DiPBI) have been found to be exceptionally effective. For example, photorefractive composites containing C12-4Cl diperylene bisimide can provide twice the photorefractive power of PCBM at only one quarter of the sensitizer concentration. It is particularly advantageous that the amount of sensitizer in photorefractive composites can be significantly reduced.

The photorefractive composite contains, in addition to a sensitizer, a hole conductor and a non-linear optical unit.

The hole conductor is preferably selected from the group consisting of polymeric carbazole derivatives, poly (p-phenylenevinylene) derivatives, N, N'-bis (3-methylphenyl) -N, N'-diphenylbenzidine, polymeric derivatives of N, N'-bis (3-methylphenyl) -N, N'-diphenylbenzidine, polythiophene, p-type rylene dyes, tri-p-tolylamine, pentacene and / or anthracene.

Non-polymeric hole conductors such as p-type rylene dyes, tri-p-tolylamine, pentacene and anthracene can be used in non-polymeric form. Preferably, these hole conductors may be used in polymer form, for example, in admixture with a polymer, such as polystyrene, or as a functional group of a polymer. Furthermore, conductive derivatives of pentacene and anthracene, in particular 6,13-bis (triisopropylsilylethynyl) pentacene (TIPS-pentacene), are preferred.

Polymeric hole conductors are preferred. Preferably, the photorefractive composite is a photorefractive polymer composite. Preferred polymeric hole conductors are selected from the group comprising polymeric carbazole derivatives, poly (p-phenylenevinylene) derivatives, polymeric derivatives of N, N'-bis (3-methylphenyl) -N, N'-diphenylbenzidine, and polythiophenes.

Preferred polymeric carbazole derivatives are selected from the group consisting of poly (N-vinylcarbazole) (PVK), poly [methyl (3-carbazol-9-yl-propyl) siloxane] (PSX-Cz) and poly (p-phenylene terephthalate) having carbazole pendant groups (PPT-Cz). Preferred poly (p-phenylenevinylene) derivatives are selected from the group consisting of poly [1,4-phenylene-1,2-di (4-benzyloxyphenyl) vinylene] (DBOP-PPV), poly [o (p) -phenylenevinylene -alt-2-methoxy-5- (2-ethylhexyloxy) -p-phenylenevinylene] (MEH-PPV) and poly [o (p) -phenylenevinylene-alt-2-methoxy-5- (2-ethylhexyloxy) -p-] phenylenevinylene] (p-PMEH-PPV). Preferred polymeric derivatives of N, N'-bis (3-methylphenyl) -N, N'-diphenylbenzidine (TPD) are selected from the group consisting of poly (acryltetraphenyldiaminobiphenol) (PATPD) and poly [2-methyl-1,4- phenylenephenylimino-4,4'-biphenylenephenylimino-3-methyl-1,4-phenylene-1,2-vinylene-2,5-dioctyloxy-1,4-phenylene-1,2-vinylene] (TPD PPV). A preferred polythiophene is poly (3-hexylthiophene-2,5-diyl).

Advantageously, such polymers can provide highly ordered crystalline thin films.

In preferred embodiments, the hole conductor is a polymeric carbazole derivative selected from the group consisting of poly (N-vinylcarbazole), poly [methyl (3-carbazol-9-yl-propyl) siloxane] and / or poly (p-phenylene terephthalate) with carbazole Includes page groups. In a preferred embodiment, the hole conductor is poly (9-vinylcarbazole).

In preferred embodiments, the composite comprises the hole conductor in an amount in the range of ≥ 1 wt .-% to ≤ 84 wt .-%, preferably in the range ≥ 10 wt .-% to ≤ 70 wt .-% and in particular in the range of ≥ 59.601 wt% to ≤ 59.807 wt% based on a total amount of the composite of 100 wt%.

The nonlinear optical units are also referred to as "nonlinear optical residues" or nonlinear optical chromophores. Since the properties are not relevant as a dye for the photorefractive effect, these elements of the photorefractive composite are referred to as nonlinear optical units (NLO).

In preferred embodiments, the non-linear optical unit is selected from the group consisting of cyanobiphenyls, dicyanostyrene derivatives, 1-alkyl-5- [2- (5-dialkylaminothienyl) methylene] -4-alkyl- [2,6-dioxo-1, 2,5,6-tetrahydropyridine] -3-carbonitrile, 2-dicyanomethylene-3-cyano-5,5-dimethyl-4- (4'-dihexylaminophenyl) -2,5-dihydrofuran, 4-N, N-diethylamino β-nitrostyrene, 3-fluoro-4- (N, N-diethylamino) -β-nitrostyrene, 2,5-dimethyl- (4-p-nitrophenylazo) anisole, 3-methoxy- (4-p-nitrophenylazo) anisole, 2-N, N-Dihexylamino-7-dicyanomethylidenyl-3,4,5,6,10-pentahydronaphthalene and / or 3- (N, N-di-n-butylanilin-4-yl) -1-dicyanomethylidene-2 cyclohexene.

Preference is given to rod-shaped non-linear optical units. In preferred embodiments, the non-linear optical unit is a cyanobiphenyl selected from the group consisting of 4 '- (n-octyloxy) -4-cyanobiphenyl (8OCB) and / or 4' - (n-pentyl) -4-cyanobiphenyl ( 5CB). Preferably, the cyanobiphenyl is 4 '- (n-pentyl) -4-cyanobiphenyl. 4 '- (n-Pentyl) -4-cyanobiphenyl is also referred to as 4-pentyl-4'-cyanobiphenyl, 4'-pentyl-4-biphenylcarbonitrile or 4-cyano-4-n-pentylbiphenyl.

Preferred dicyanostyrene derivatives are selected from the group consisting of 2- [4-bis (2-methoxyethyl) aminobenzylidene] -malononitrile (AODCST), 4-piperidinobenzylidenemalononitrile (PDCST) and 2- (4-azepan-1-yl-benzylidene) malononitrile (7-DCST).

Advantageously, rod-shape-like non-linear optical units can be rearranged more easily in the polymer when a space-charge field is formed.

In preferred embodiments, the composite comprises the nonlinear optical unit in an amount in the range of ≥5 wt% to ≤85 wt%, preferably in the range ≥20 wt% to ≤65 wt%, and especially in the range from ≥ 40.052 wt% to ≤ 40.187 wt% based on a total amount of the composite of 100 wt%.

In a preferred embodiment, the composite comprises poly (9-vinylcarbazole), 4 '- (n -pentyl) -4-cyanobiphenyl, and C12-4Cl-diperylenebisimide in a ratio ranging from 59.802: 40.187: 0.010% by weight to 59.736: 40.142: 0.122% by weight, and preferably in a ratio of 59.601: 40.052: 0.348% by weight.

Advantageously, even low concentrations of C12-4Cl diperylenebisimide (C12-4Cl-DiPBI) are exceptionally effective, and the amount of photosensitizer in the composite can therefore be reduced.

The hole conductor is preferably a polymeric hole conductor. With respect to polymers having a weight in the range of from 25,000 to 50,000 g / mol, in particular having an average weight of 37,500 g / mol, the composite preferably comprises C12-4Cl-diperylenebisimide (C12-4Cl DiPBI) in an amount in the range of ≥ 0.001 mol% to ≤ 1 mol%, preferably in the range of ≥ 0.002 mol% to ≤ 0.2 mol% and in particular in the range of ≥ 4.25 mmol% to ≤ 136 mmol%; the hole conductor in an amount in the range of ≥ 0.5 mol% to ≤ 1.5 mol%, preferably in the range of ≥ 0.9 mol% to ≤ 1 mol% and in particular in the range of ≥ 0.983 mol% to ≤ 0.984 mol %; and the non-linear optical unit in an amount in the range of ≥ 97.5 mol% to ≤ 99.5 mol%, preferably in the range of ≥ 98.5 mol% to ≤ 99.2 mol% and in particular in the range of ≥ 98.881 mol % to ≤ 99.016 mol% based on a total amount of the composite of 100 mol%. Preferably, the ratio of poly (9-vinylcarbazole), 4 '- (n -pentyl) -4-cyanobiphenyl and C12-4Cl-diperylenebisimide in the photorefractive composite is in the range of 0.979: 98.974: 0.047 mol% to 0.979: 99.017: 0.004 mol % and especially in a ratio of 0.983: 98.881: 0.136 mol%.

The photorefractive composite may further include plasticizers and / or sensitizers. Preferred plasticizers are selected from the group comprising N-ethylcarbazole, butylbenzyl phthalate, diphenyl phthalate, diisooctyl phthalate and N- (2-ethylhexyl) -N- (3-methylphenyl) -aniline. Preferred sensitisers are selected from the group comprising fullerenes and / or derivatives of 2,4,7-trinitro-9-fluorenone. Preferred fullerenes are selected from the group consisting of fullerene, the fullerene in the form of (C60-Ih) [5,6] and C ₇₀ -D _{5h (6)} comprises fullerene or [6,6] -phenyl-C61-methyl butyrate. A preferred derivative of 2,4,7-trinitro-9-fluorenone is (2,4,7-trinitro-9-fluorenylidene) malononitrile.

The photorefractive composite may further comprise tris (8-hydroxyquinolinato) aluminum, polystyrene, nanoparticles, quantum dots and / or carbon nanotubes. Tris (8-hydroxyquinolinato) aluminum, for example, can be used as a dopant for conditional traps. Polystyrene can be used to stabilize the composite.

Another aspect of the invention relates to the use of C12-4Cl diperylene bisimide as a sensitizer in a photorefractive composite comprising a hole conductor and a non-linear optical unit.

Advantageously, it has been found that C12-4Cl-diperylenebisimide (C12-4Cl-DiPBI) can be used as a broad-spectrum photosensitizer with excellent optical and physical properties. In particular, the broad absorption spectrum of C12-4Cl diperylene bisimide (C12-4Cl-DiPBI) can provide a prerequisite for excellent processability of photorefractive materials over the full range of visible light.

The photorefractive composite can be used for applications such as high density holographic data storage, holographic imaging of living tissue, and 3D real-time image displays. The photorefractive composite is particularly advantageous as a refractive index modulation high performance material in data storage, medical diagnostics and the entertainment industry. Furthermore, the photorefractive composite can be used to realize nanophotonic optical information processing devices.

Another aspect of the invention relates to the use of a photorefractive composite according to the invention in holography techniques, particularly in holographic data storage devices and holographic displays.

The photorefractive composite can be used in the field of holography, particularly holographic data storage and medical diagnostics. The photorefractive composite can even be used for realistic holographic projection of people and lifeless objects in virtual reality. In particular, the photorefractive composite can be used for holographic displays, for example for holographic imaging of living tissue. Fast write and erase times of the photorefractive composite enable use in 3D color displays.

Furthermore, the photorefractive composite can be used in dynamic holographic gratings, for example solar collimators. In addition, the photorefractive composite can be used in such implementations as updateable 3D displays or data storage devices. Further, the photorefractive composite may be used, for example, as a switch or beam splitter in an optical computer.

Further, the photorefractive composite can be used in optics and laser optics. In particular, the photorefractive composite may be used as an optical switch, a beam splitter, or an intensity controller. The photorefractive composite can also be used as a wave plate.

Further, the photorefractive composite can be used in photovoltaic cells, organic field effect transistors (OFETs), and organic light emitting diodes (OLEDs). The photorefractive composite can be used especially in fiber optic communication. Further, the photorefractive composite can be used in place of inorganic crystals in microscopy and measurement techniques.

Another aspect of the present invention relates to a holographic data storage device or holographic display comprising a photorefractive composite according to the invention.

Another aspect of the present invention relates to an optical switch, in particular a beam splitter or intensity regulator comprising a photorefractive composite according to the invention.

Furthermore, another aspect of the invention relates to an organic semiconductor, in particular a photovoltaic cell, an organic field-effect transistor or an organic light-emitting diode, which comprises a photorefractive composite according to the invention.

Unless defined otherwise, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The following examples are intended to illustrate and not limit the scope of the invention. It will be understood that although there is at least one exemplary embodiment, there are a large number of variations.

In the figures shows

1 Absorption spectra of a photorefractive composite without sensitizer and photorefractive composites comprising a molecular weight of 136 mmol% of the sensitizers PCBM or C12-4Cl-DiPBI.

2 the photoconductivity I _{ph of} the photorefractive composites with a molecular weight of 136 mmol% of the sensitizers PCBM or C12-4Cl-DiPBI as a function of the electric field.

3 the birefringence of the photorefractive composites with a molecular weight of 136 mmol% of the sensitizer PCBM or 34 mmol% or 136 mmol% of the sensitiser C12-4Cl-DiPBI as a function of the electric field.

4 the coefficient of enhancement Γ of the photorefractive composites with a molecular weight of 136 mmol% of the sensitizer PCBM or 34 mmol% or 136 mmol% of the sensitiser C12-4Cl-DiPBI as a function of the electric field.

5 the kinetics of energy transfer between two laser beams at 70 V / μm using photorefractive composites with a molecular weight of 136 mmol% of the sensitizer PCBM or 34 mmol% or 136 mmol% of the sensitiser C12-4Cl-DiPBI.

6 the writing speed, represented as the reciprocal time constant, as a function of the concentration of C12-4Cl-DiPBI in the photorefractive composites.

example 1

Preparation of indium tin oxide electrodes comprising a photorefractive composite

1.1. Structuring of the indium tin oxide electrode

Since the photorefractive composite is an amorphous solid, a high voltage must be applied to the sample to induce an axis of symmetry. A float glass (precision Glas und Optik GmbH) with single-sided indium tin oxide (ITO) coating was used as transparent electrodes. This electrode type is used for photoconductivity measurements. The size of the glass was 30 mm × 30 mm × 0.7 mm, and the 100 nm thick ITO layer covered a 26 nm SiO ₂ passivation layer. The electrode was washed by etching HCl structured. The electrode was patterned to provide a well-defined circular area of 38.5 mm ² and a diameter of 7 mm, which was patterned to match the diameter of the power sensor. The electrode could be illuminated homogeneously with an expanded beam.

1.2. Production of the composite

C12-4Cl diperylene bisimide was prepared according to the reaction conditions of H. Qian, Z. Wang, W. Yue, D. Zhu, J. Am. Chem. Soc. 2007, 129, 10664, synthesized. The polymeric poly-9-vinylcarbazole (PVK), the liquid crystal 4 '- (n-pentyl) -4-cyanobiphenyl (5CB) and the sensitizer [6,6] -phenyl-C61-butyric acid methyl ester (PCBM) used for comparison was acquired by Sigma Aldrich. The polymeric poly-9-vinylcarbazole (PVK) had a weight in the range of 25,000 to 50,000 g / mol. To calculate the concentrations in mol%, an average weight of 37,500 g / mol was used.

30 mg of poly-9-vinylcarbazole (PVK), 20 μl of 4 '- (n-pentyl) -4-cyanobiphenyl (5CB) and the desired amount of sensitizer were dissolved in 200 μl of chloroform under ultrasound in a bottle in a viscous substance.

The concentration of the sensitizer to give 136 mmol% [6,6] -phenyl-C61-butyric acid methyl ester (PCBM) was added in the form of 10 μl of a 10 mg / ml solution in chloroform. The concentration of sensitizer to give 136, 102, 68, 54.4, 40.8, 34, 17, 8.5 and 4.25 mmol% C12-4Cl-DiPBI was in the form of 100 μl, 75 μl , 50 μl, 40 μl, 30 μl, 25 μl, 12.5 μl, 6.25 μl and 3.125 μl of a 1.75 mg / ml solution of C12-4Cl-DiPBI in chloroform.

1.3. melt pressing

Melt pressing is a common process for producing photorefractive samples. The prepared composites comprising C12-4Cl-DiPBI or PCBM were pipetted bubble-free onto an ITO electrode and dried in ambient air for 20 minutes. Since the boiling point of chloroform is 62 ° C, it vaporizes very rapidly even at room temperature. Thereafter, the nearly dried composite was annealed for one hour at 55 ° C in the oven to remove the remainder of the solvent. These steps were repeated four times until the desired thickness was achieved. Then, the composite was melted at 90 ° C and covered with the second glass plate to be pressed by its weight to the thickness of the spacer layer. The spacer layer was a transparent film with a defined thickness of 50 microns, and the pressing took one hour. Finally, the sample was slowly cooled to room temperature.

Example 2

Measurement of absorption spectra

Indium-tin oxide electrodes with photorefractive composites containing 136 mmol% of C12-4Cl diperylene bisimide or the comparative sensitizers [6,6] -phenyl C61-butyric acid methyl ester (PCBM) or according to Example 1 were used to measure the absorption spectra were made.

The photorefractive composite with C12-4Cl diperylene bisimide comprised poly (9-vinylcarbazole) (PVK), 4-cyano-4-n-pentylbiphenyl (5CB), and C12-4Cl-DiPBI in a ratio of 0.983: 98.881: 0.136 mol%. The comparative photorefractive composite comprised poly (9-vinylcarbazole) (PVK), 4-cyano-4-n-pentylbiphenyl (5CB) and PCBM in a ratio of 0.983: 98.881: 0.136 mol%.

The absorption spectra of the photorefractive composites were measured by the JascoV-530 UV / VIS spectrometer. Using the relationship A = d × α and assuming that the glass of the samples was non-absorbent, the absorption coefficient of 9 cm ^-1 for the PCBM sample was calculated from two samples having a thickness of d = 50 μm and d = 100 μm. The results of the composite preparations with C12-4Cl-DiPBI, which in 1 were obtained by measuring the intensity of the transmitted light behind the sample with a photodiode and correlating these values with the sample containing PCBM.

As in 1 As can be seen, the absorption of the photorefractive composite with C12-3Cl-DiPBI covered the full range of visible light, with peaks in the blue, green and red regions observed. This shows that C12-4Cl-DiPBI is particularly advantageous as a sensitizer to the hardly absorbent PCBM composite.

The photorefractive composite with C12-4Cl-DiPBI had a dielectric constant of 2.9 and a glass transition temperature in the range of room temperature. The photorefractive composite remained crystallization-free for at least six months and was able to withstand electric fields of 80 V / μm.

Example 3

Measurement of photoconductivity

For measuring the photoconductivity indium-tin oxide electrodes were used with photorefractive composites containing a molecular weight of 136 mmol% of sensitiser [6,6] -phenyl-C61-butyric acid methyl ester (PCBM) or prepared according to Example 1 sensitizer C12-4Cl-diperylenebisimide exhibited.

To measure the photoconductivity, the defined electrode area of 38.5 mm ^{2 of} the indium-tin oxide electrodes was illuminated with an expanded Gaussian beam. The conductivity measurement arrangement was as follows: the intensity of a frequency doubled Nd: YAG (neodymium-doped yttrium aluminum garnet; Nd: Y ₃ Al ₅ O ₁₂ ) CW laser beam (Compass 315 m 100, Coherent) of 532 nm wavelength changed using a half-wave plate and a polarization beam splitter. The light passing through the open aperture was expanded by a concave lens which provided the homogeneous illumination of the sample. The intensity used for the measurement was 16 mW / cm ² . High voltage was applied to the sample by a high voltage source (Heinzinger LNC 10000-5 neg) and controlled via an NI box (USB-6009). A picoammeter (Keithley 6485 Picoammeter) was incorporated into the electrical circuit which included the indium-tin oxide electrodes with the photorefractive composite and the high voltage source for measuring dark current and photocurrent. The photocurrent I _ph results from the subtraction of the dark current I _d from the total current I _tot .

The measurement procedure was as follows: to allow sufficient time for electrical relaxation processes in the circuit, a stepwise application of the electric field of 40 V / μm to the sample was applied within 2 minutes. The measurement was started at a time defined as t = 0 s. The aperture was opened at t = 10 s and closed at t = 120 s. The measurement was stopped at t = 150 s. These steps were repeated with increasing the electric field of 40 V / μm in steps of 2 V / μm to 70 V / μm. After applying each next voltage, a 30 second dark current pause was taken to reach a constant value. The time resolution was 60 ms. The current resolution of the picoammeter was 10 fA.

The photoconductivity I _{ph of} the photorefractive composites with a molecular weight of 136 mmol% of the sensitizers PCBM or C12-4Cl-DiPBI as a function of the electric field is in 2 shown. Again 2 It can be seen that the composite with C12-4Cl-DiPBI had an absorption at 532 nm above that of the composite with PCBM and therefore produced a higher photocurrent. This means that less voltage must be applied to the composite with C12-4Cl-DiPBI to give a comparable photocurrent. For example, if 50V is applied at a thickness of 50μm corresponding to 1V / μm, the composite with C12-4Cl-DiPBI will provide a photocurrent of 4.2nA while the composite with PCBM will provide a photocurrent of 0.1nA supplies.

Example 4

transmission ellipsometry

To study the contribution of the orientation of the liquid crystal to the photorefractive properties, an ellipsometry measurement was performed.

Indium-tin oxide electrodes with photorefractive composites containing a molar amount of 136 mmol% of [6,6] -phenyl-C61-butyric acid methyl ester (PCBM) or 34 mmol% or 136 mmol% of the C12 reagent prepared according to Example 1 were used. 4Cl-Diperylenbisimid had.

In the measurement of the transmission ellipsometry, the electrodes were placed between two + 45 ° and -45 ° polarizers and rotated 45 °. During milliseconds, a high electric field strength between 40 V / μm and 70 V / μm was applied, which corresponded to a voltage between 2 kV and 3.5 kV for a sample thickness of 50 μm, and the liquid crystals were oriented parallel to the electric field and set one birefringence characteristic of the composite. The 45 ° polarized laser beam was rotated around the composite and detected by a photodiode.

The arrangement and physical processes of measuring the transmission ellipsometry were as follows: A half wave plate and a + 45 ° polarizer produced a laser beam with the direction of the electric field vector consisting of a component parallel (p) to and perpendicular (s) to the plane of light incidence , The light entered the sample electrode, which was rotated 45 ° with respect to the incoming beam. Since it was assumed that the refractive index of the sample was 1.7, the angle within the composite calculated using Snell's law was 25 °. The voltage applied to the sample by a high voltage source (TREK 609E-6) was controlled by an arbitrary waveform generator (hp 33120A) and broke the central symmetry. A photodiode after a -45 ° polarizer detected the intensity of the light passing through the -45 ° polarizer. The signal was through a Signal amplifier (FEMTO DHPCA-100) amplified, which converted the photocurrent of the diode into voltage, which was measured with an NI box (USB-6009). The intensity I was therefore proportional to the voltage U.

The ellipsometry measurement was made at a wavelength of 532 nm and the laser beam power was kept at 100 μW. The measurement procedure was as follows: I ₀ was measured with the -45 ° polariser set parallel to the first + 45 ° polarizer and without any electric field applied to the sample. The second polarizer was set perpendicular to the first, and the measurement was started at a time defined as t = 0 s. An electric field E = 40 V / μm was applied to the sample at t = 10 s within a few milliseconds. The electric field was switched off at t = 40 s within a few milliseconds, and the measurement was stopped at t = 60 s. These steps were repeated with increasing the electric field of 40 V / μm in steps of 2 V / μm to 70 V / μm. The time and voltage resolution were 1 ms and 0.5 mV, respectively. The steady state value was used to calculate the electro-optical response.

The birefringence of photorefractive composites with a molecular weight of 136 mmol% PCBM or 34 mmol% or 136 mmol% C12-4Cl-DiPBI is in 3 as a function of the electric field. As in 3 As can be seen, the composite with only 34 mmol% C12-4Cl-DiPBI still had twice as high absorption as the composite with 136 mmol% PCBM.

Example 5

Measurement of photorefractive power by two-beam coupling

Two-beam coupling was used to study the stationarity properties and kinetics of photorefractive materials. The two-beam coupling process is the interaction of two coherent laser beams with the simultaneously induced index grating. The energy exchange between the beams does not only depend on the amplitude of the space charge field, but is strongly influenced by the value of the phase shift between the index modulation and the interference pattern. Therefore, if this phase shift is 0, which z. B. is the case for thick absorption grid, there is no energy transfer. Thus, a confusion of other physical mechanisms with the photorefractive effect can be avoided. The energy exchange is characterized by the gain coefficient Γ, which is given in units of cm ^-1 .

The arrangement of the two beam coupling was as follows: A laser beam was split by a polarization beam splitter into two beams whose intensity could be changed by a first half wave plate placed in front of the polarization beam splitter. The wavelength of the laser was 532 nm, and the intensity of each beam measured before the sample was 8 mW / cm ² . Since the polarizations of the two beams were different (beam 1 was p-polarized while beam 2 was s-polarized), a second half-wave plate was introduced into beam 2 to achieve a 90 ° rotation of the polarization. As a result, both beams were p-polarized.

Rays 1 and 2 intersected within the sample, which was poled with a high voltage source (Heizinger LNC 10000-5 neg). It is important to intentionally apply a high negative voltage to the first electrode to avoid beam fan-out. In this approach, the energy was transferred from beam 2 to beam 1. The sample was tilted with respect to beam 1 by α = 40 ° and beam 2 by α + β = 60 °. This geometry is advantageous for providing a high projection value of the grating vector on E. The already calculated grid spacing was about 2 μm.

The energy transfer between the two beams was observed by the detection of light intensity across two photodiodes. A fast photodiode detected the intensity of beam 1, and a subsequent current amplifier (FEMTO DHPCA-100) converted the photocurrent into voltage U received through an NI box (USB-6009). The intensity of beam 2 was monitored with a Coherent Fieldmaster for a shutter placed after opening the second half-wave plate.

The measurement procedure was as follows: The electric field was slowly increased to E = 40 V / μm. The field remained applied for 30 seconds before the measurement of the light intensity started and the shutter was opened. This time was required for the liquid crystal to align parallel to the electric field, as deduced from the ellipsometry measurements.

Therefore, the kinetics of energy transfer can be attributed to photoconductive processes. The measurement of I from beam 1 was started at a time defined as t = 0 s with the shutter kept closed. The aperture was opened at t = 5 s and closed upon reaching stationarity at t = 85 s for the PCBM samples and at t = 45 s for the C12-4Cl DiPBI samples. The measurement was stopped at t = 100 s for the PCBM sample and at t = 60 s for the C12-4Cl DiPBI samples. These steps were repeated with increasing the electric field of 40 V / μm in steps of 2 V / μm to 70 V / μm. The time and voltage resolution were 1 ms and 0.5 mV, respectively.

The coefficient of enhancement Γ of photorefractive composites with a molecular weight of 136 mmol% of the sensitizer PCBM or 34 mmol% or 136 mmol% of the sensitiser C12-4Cl-DiPBI is in 4 as a function of the electric field. As in 4 As can be seen, the photorefractive composites with 34 mmol% C12-4Cl-DiPBI had a reinforcement coefficient Γ which was twice as high as the reinforcement coefficient Γ of the photorefractive composites with 136 mmol% PCBM. The photorefractive composites with 136 mmol% C12-4Cl-DiPBI had a lower gain coefficient Γ, but reached it faster.

5 shows the writing speed of the grid. In 5 The kinetic energy transfer is represented as the gain γ as a function of time between the two beams at 70 V / μm of the photorefractive composites, which has a molecular weight of 136 mmol% of the sensitizer PCBM or 34 mmol% or 136 mmol% of the sensitiser C12- 4Cl-DiPBI include. Five seconds after the start of the measurement, the aperture for beam 2 was opened and the writing of the grid was started. This is effected by an energy transfer between the beams 1 and 2, and 5 represents the energy yield of the beam. It is believed that the fast writing speeds of composites with C12-4Cl-DiPBI are based on the higher absorption and resulting photoconductivity.

Using a double exponential function corresponding to the writing graph, two time constants can be determined. A fast constant t ₁ is influenced by the process of charge generation and charge transport, while the orientation of the liquid crystals contributes to the second, slower constant t ₂ .

6 shows the writing speed and represents the reciprocal time constant t ₁ as a function of the concentration of C12-4Cl-DiPBI in the photorefractive composites. Photorefractive composites with concentrations of 4.25, 8.5, 17, 34, 40.8, 54.4, 68, 102 and 136 mmol% C12-4Cl DiPBI.

For the PCBM composite, the reciprocal of the fast time constant was 0.14 s ^-1 . The slowest photorefractive C12-4Cl-DiPBI composite was 10 times faster, while the fastest photorefractive C12-4Cl-DiPBI composite was 100 times faster.

For the PCBM composite with 136 mmol% PCBM, the reciprocal of the second time constant was 80 s. Even the slowest photorefractive C12-4Cl-DiPBI composite was nearly twice as fast as the PCBM composite. This shows that the photorefractive C12-4Cl-DiPBI composites are significantly faster than the PCBM composite.

These experiments show that the absorption of the photorefractive composites with C12-4Cl-DiPBI captures the full range of visible light and thus confers photoconductivity on the composites. The rod-like molecules are capable of orienting in an electric field. These capabilities can produce a strong and fast photorefractive effect even at low concentrations of C12-4Cl-DiPBI.

Claims (14)

A photorefractive composite comprising a hole conductor, a non-linear optical unit and a sensitizer, wherein the sensitizer is C12-4Cl diperylene bismuth according to the following formula (1):

A composite according to claim 1 wherein the composite comprises C12-4C1 diperylene bisimide in an amount in the range of ≥ 0.001 wt% to ≤ 1 wt%, preferably in the range of ≥ 0.002 wt% to ≤ 0.5 wt%. %, in particular in the range of ≥ 0.01% by weight to ≤ 0.348% by weight and more particularly in the range of ≥ 0.01% by weight to ≤ 0.122% by weight, based on a total amount of the composite of 100% by weight. A composite according to claim 1 or 2, wherein the hole conductor is selected from the group comprising polymeric carbazole derivatives, poly (p-phenylenevinylene) derivatives, N, N'-bis (3-methylphenyl) -N, N'-diphenylbenzidine, polymeric derivatives of N, N'-bis (3-methylphenyl) -N, N'-diphenylbenzidine, polythiophenes, p-type rylene dyes, tri-p-tolylamine, pentacene and / or anthracene. A composite according to any one of the preceding claims, wherein the hole conductor is a polymeric carbazole derivative selected from the group consisting of poly (N-vinylcarbazole), poly [methyl (3-carbazol-9-yl-propyl) siloxane] and / or poly (p-phenylene terephthalate) selected with carbazole side groups and is preferably poly (9-vinylcarbazole). A composite according to any one of the preceding claims, wherein the composite material comprises the hole conductor in an amount in the range of ≥ 1 wt% to ≤ 84 wt%, preferably in the range ≥ 10 wt% to ≤ 70 wt%, and in particular in the range of ≥ 59.601% by weight to ≤ 59.807% by weight based on a total amount of the composite of 100% by weight. A composite according to any one of the preceding claims wherein the non-linear optical unit is selected from the group consisting of cyanobiphenyls, dicyanostyrene derivatives, 1-alkyl-5- [2- (5-dialkylaminothienyl) methylene] -4-alkyl- [2,6-dioxo] 1,2,5,6-tetrahydropyridine] -3-carbonitrile, 2-dicyanomethylene-3-cyano-5,5-dimethyl-4- (4'-dihexylaminophenyl) -2,5-dihydrofuran, 4-N, N- Diethylamino-β-nitrostyrene, 3-fluoro-4- (N, N-diethylamino) -β-nitrostyrene, 2,5-dimethyl- (4-p-nitrophenylazo) anisole, 3-methoxy- (4-p-nitrophenylazo) anisole, 2-N, N-dihexylamino-7-dicyanomethylidenyl-3,4,5,6,10-pentahydronaphthalene and / or 3- (N, N-di-n-butylanilin-4-yl) -1-dicyanomethylidene 2-cyclohexene is selected. A composite according to any one of the preceding claims, wherein the non-linear optical unit is a cyanobiphenyl selected from the group comprising 4 '- (n-octyloxy) -4-cyanobiphenyl and / or 4' - (n-pentyl) -4-cyanobiphenyl, and preferably 4 '- (n-pentyl) -4-cyanobiphenyl. A composite according to any one of the preceding claims, wherein the composite comprises the nonlinear optical unit in an amount in the range of ≥ 5% to ≤ 85%, preferably in the range ≥ 20% to ≤ 65% by weight. and in particular in the range of ≥ 40.052% by weight to ≤ 40.187% by weight, based on a total amount of the composite of 100% by weight. A composite according to any one of the preceding claims, wherein the composite comprises poly (9-vinylcarbazole), 4 '- (n-pentyl) -4-cyanobiphenyl and C12-4Cl-diperylenebisimide in a ratio in the range of 59,802: 40,187: 0.010% by weight. to 59.736: 40.142: 0.122% by weight, and preferably in a ratio of 59.601: 40.052: 0.348% by weight. Use of C12-4Cl diperylene bisimide as a sensitizer in a photorefractive composite comprising a hole conductor and a non-linear optical unit. Use of a photorefractive composite according to one of the preceding claims in holography techniques, in particular in holographic data storage devices and holographic displays, in optics and laser optics, in particular as an optical switch, a beam splitter or an intensity controller, or in photovoltaic cells, organic field effect transistors and organic light emitting diodes. A holographic data storage device or holographic display comprising a photorefractive composite according to any one of claims 1 to 9. An optical switch, in particular a beam splitter or intensity regulator, comprising a photorefractive composite according to any one of claims 1 to 9. An organic semiconductor, in particular a photovoltaic cell, an organic field-effect transistor or an organic light-emitting diode, comprising a photorefractive composite according to one of claims 1 to 9.

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