GB2542563A - Pentacene derivatives with C-alkyne solubilising units and their applications as small molecule organic semiconductors - Google Patents

Abstract

Alkynyl pentacene derivatives of formula (I): wherein Ra is a solubilising group of formula (II) where R9 and R11 are C1-4alkyl, and R10 is hydrogen, C1-4alkyl or C1-3alkoxy; R1-R8 are hydrogen, fluorine or C1-4alkyl; may be useful to form organic thin films. The use of these solubilising group-containing pentacenes in electronic devices and components, for example organic field effect transistors or organic light emitting diodes, is also outlined. By providing specific C-alkyne side chains at the pentacene scaffold as solubilising groups and optional fluorine or alkyl substituents, compounds small molecule organic semiconductors that exhibit a high solubility and thermal stability during solution processing and at the same time show high field effect mobility and favourable π-π stacking may be manufactured.

Description

PENTACENE DERIVATIVES WITH C-ALKYNE SOLUBILISING UNITS AND THEIR APPLICATIONS AS SMALL MOLECULE ORGANIC SEMICONDUCTORS

FIELD OF INVENTION

[0001] This invention relates to novel pentacene derivatives with specific C-alkyne side chains, organic thin films comprising these derivatives, their use in electronic devices and components and methods of manufacturing the same.

BACKGROUND OF THE INVENTION

[0002] In the recent years, there has been increased interest in the development of small-molecule organic electronic materials as alternatives to inorganic semiconductors, such as silicon-based semiconductors, as they are lightweight, provide a high flexibility and allow manufacturing and processing of electronic devices at relatively low costs. Typically applied within thin films, such organic semiconductors find use in a large number of electronic devices, such as displays (including organic light-emitting diodes (OLED)), photovoltaics, and electronic circuits and components (e.g. organic field effect transistor (OFET) devices).

[0003] Ideally, organic semiconductors exhibit high charge carrier mobility or high field effect mobility, respectively, and favourable ττ-π stacking. Organic semiconductors fulfilling these criteria tend to be those which comprise compounds having a rigid planar structure and extensively conjugated π-systems allowing for the movement of electrons. In addition, it is of utmost importance that organic semiconductors are both highly soluble and thermally stable during solution processing.

[0004] Benzothiophene derivatives, such as e.g. thieno[3,2-b:4,5-b’]bis[1]benzothiophene, have been shown to represent promising candidates in terms of performance in organic field effect transistors. However, these materials typically exhibit a solubility too low to produce high-quality single component thin films and thus require blending with polymer binder systems.

[0005] Efforts have been made to modify benzothiophene derivatives with different alkyl substituents in order to enhance their solubility. However, substitution with relatively long alkyl chains often leads to a decrease in solubility due to strong Van der Waals interactions between the molecules. While using branched alkyl chains may improve solubility, it tends to be accompanied with decreasing charge carrier mobility.

[0006] Pentacene derivatives, specifically alkyne-functionalized pentacenes, another class of small-molecule organic semiconductors, tend to exhibit a better solubility in organic solvents than benzothiophenes. As a prominent example thereof, 6,13-bis[(triisopropyl-silyl)ethynyl] pentacene, commonly referred to as “TIPS-pentacene” may be mentioned (see e.g. US 6,690,029 B1). Nevertheless, the charge carrier mobility of these compounds also leaves room for improvement.

[0007] In view of the above, it is desirable to provide compounds that exhibit high solubility and thermal stability during solution processing and at the same time show improved field effect mobility and favourable ττ-π stacking when compared to known pentacene based materials.

SUMMARY OF THE INVENTION

[0008] The present invention solves this object with the subject matter of the claims as defined herein. The advantages of the present invention will be further explained in detail in the section below and further advantages will become apparent to the skilled artisan upon consideration of the invention disclosure.

[0009] In the search for soluble, small molecule organic semiconductor materials for thin film transistor device applications, materials that exhibit a crystalline structure enabling a high field effect mobility and an improved solubility as compared to known pentacene-based materials have been studied. The present inventors surprisingly found that implementing specific solubilising groups at the alkyne side chains enables preferential molecular stacking in the solid crystal and provides a solution to the abovementioned problems.

[0010] Generally speaking, in one aspect the present invention relates to a pentacene derivative represented by the following General Formula (I):

(I) wherein R1 to R8 are independently selected from a hydrogen atom, a fluorine atom and an alkyl group having 1 to 4 carbon atoms; and wherein Ra is a solubilising group represented by the following General Formula (II):

(II) with R9 and R11 being independently selected from an alkyl group having 1 to 4 carbon atoms; and R10 being selected from any of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 3 carbon atoms.

[0011] Further preferred embodiments of the pentacene derivatives of the present invention are specified in the claims and the following description.

[0012] In a further aspect, the present invention relates to an improved method of synthesizing the aforementioned pentacene derivatives.

[0013] Also, the invention relates to methods for the preparation of organic thin films comprising the aforementioned pentacene derivatives and the use of said compounds and organic thin films as semiconducting material in electronic devices or components, as well as to electronic devices or components comprising said organic thin films.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Fig. 1 schematically illustrates the general architecture of a conventional bottom-gate organic thin film transistor.

[0015] Fig. 2 schematically illustrates a pixel comprising an organic thin film transistor and an adjacent organic light-emitting device fabricated on a common substrate.

[0016] Fig. 3 schematically illustrates a stacked configuration comprising an organic thin film transistor and an organic light-emitting device.

[0017] Fig. 4A, Fig. 4B, and Fig. 4C show comparisons of the hole mobilities, transfer integrals and reorganization energies between TIPS-pentacene and a compound of the present invention as determined via LC-wPBE/6-31G* [0018] Fig. 5 shows experimental and calculated stacking structures of TIPS-pentacene and a compound of the present invention (optimized by LC-wPBE/6-31G*) [0019] Fig. 6 shows the hole mobility performance (B3LYP/6-31G*) of compounds of the present invention in comparison with that of TIPS-pentacene.

DETAILED DESCRIPTION OF THE INVENTION

[0020] For a more complete understanding of the present invention, reference is now made to the following description of the illustrative embodiments thereof:

PENTACENE DERIVATIVES

[0021] In a first embodiment, the present invention relates to pentacene derivatives, the most general structure of which may be represented by the following General Formula (I):

(I) wherein R1 to R8 are independently selected from a hydrogen atom, a fluorine atom and an alkyl group having 1 to 4 carbon atoms; and wherein Ra is a solubilising group represented by the following General Formula (II):

(II) with R9 and R11 being independently selected from an alkyl group having 1 to 4 carbon atoms; and R10 being selected from any of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 3 carbon atoms.

[0022] The above compounds according to General Formula (I) have been shown to exhibit favourable ττ-π stacking and a high field effect mobility while being sufficiently soluble to be applied by a large variety of solution deposition techniques.

[0023] In a preferred embodiment, R9 and R11 in General Formula (II) are independently selected from a methyl group, an ethyl group, an isopropyl group, or a tert-butyl group; and R10 is selected from any of a hydrogen atom, a methyl group, an ethyl group, an isopropyl group, a tert-butyl group, and an alkoxy group having 1 to 3 carbon atoms.

[0024] In a further preferred embodiment, R10 is selected from any of a hydrogen atom, a methyl group, an ethyl group, an isopropyl group, or a tert-butyl group, and R9 and R11 are selected from an isopropyl group or a tert-butyl group. Alternatively, it is preferable that R10 is an alkoxy group having 1 to 3 carbon atoms, and R9 and R11 are selected from a methyl group, an ethyl group, an isopropyl group, or a tert-butyl group.

[0025] In a preferred embodiment, the alkoxy group having 1 to 3 carbon atoms is a methoxy group.

[0026] Preferably, R9 and R11 in General Formula (II) are identical.

[0027] The substituents R1 to R8 in General Formula (I) are independently selected from a hydrogen atom, a fluorine atom and an alkyl group having 1 to 4 carbon atoms, the preferred alkyl group being a methyl group.

[0028] In a preferred embodiment, R2, R3, R6 and R7 in General Formula (I) are independently selected from a hydrogen atom and a fluorine atom.

[0029] It is preferable that the substituents R2, R3, R6 and R7 in General Formula (I) are each a hydrogen atom.

[0030] Each of the substituents R1 to R8 may be identical or different. However, it is preferable that R1 and R8 are identical, R2 and R7 are identical, R3 and R6 are identical, and/or R4 and R5 are identical.

[0031] Moreover, it is preferable that the substituents R1, R4, R5 and R8 in General Formula (I) are independently selected from a fluorine atom and an alkyl group having 1 to 4 carbon atoms. It has been found that the introduction of fluorine atoms into the pentacene skeleton lowers both the HOMO and LUMO energy levels, which facilitates electron injection. Moreover, the C-H - F interactions between the C-alkyne side chain and the fluorine atom on the core have been found to play an important role in the solid state supramolecular organization, originating a typical π-stack arrangement which enhances the charge carrier mobility. Accordingly, in a preferred embodiment, R1, R4, R5 and R8 represent a fluorine atom.

[0032] In addition, it has been found that alkyl substituted pentacenes exhibit a lower oxidation potential than the unsubstituted pentacene, which may lead to improved charge injection while maintaining the preferential molecular packing motif. Hence, in another preferred embodiment, R1, R4, R5 and R8 represent an alkyl group having 1 to 4 carbon atoms, preferably a methyl group.

[0033] Alternatively preferred are mixed structures, wherein R1 and R8 each represent a fluorine atom and R4 and R5 each represent a hydrogen atom, or wherein R1 and R8 each represent an alkyl group having 1 to 4 carbon atoms, preferably a methyl group and R4 and R5 each represent a hydrogen atom, or wherein R1 and R8 each represent a fluorine atom and R4 and R5 each represent an alkyl group having 1 to 4 carbon atoms, preferably a methyl group.

[0034] From the viewpoint of an especially favourable balance of solubility properties and an excellent charge carrier mobility, it is preferable to select a substituent in accordance to any of the structural formulae (1-1) to (1-12) as solubilising group Ra:

(1-7) (1-8) (1-9) (1-10) (1-11) (1-12) [0035] It will be appreciated that the preferred features specified above may be combined in any combination, except for combinations where at least some of the features are mutually exclusive.

[0036] A number of exemplary compounds illustrating the present invention is listed in the following:

(1) (2) (3)

(4) (5) (6)

(7) (8) (9)

(10) (11) (12)

(13) (14) (15)

(16) (17) (18)

(19) (20) (21)

(22) (23) (24)

(25) (26) (27)

(28) (29) (30)

(31) (32) (33)

(34) (35) (36)

(37) (38) (39)

(40) (41) (42)

(43) (44) (45)

(46) (47) (48)

(49) (50) (51)

(52) (53) (54)

(55) (56) (57)

(58) (59) (60)

(61) (62) (63)

(64) (65) (66)

(67) (68) (69)

(70) (71) (72)

(73) (74) (75)

(76) (77) (78)

(79) (80) (81)

(82) (83) (84)

SYNTHESIS OF PENTACENE DERIVATIVES

[0037] The compounds of the present invention may be synthesized according to or in analogy to methods known to the skilled artisan.

[0038] An exemplary synthetic route for compound (1) is shown in the following reaction scheme:

[0039] While the above synthesis method may be suitable for pentacene derivatives having no substituents other than the C-alkyne solubilising units at the pentacene core, however, finding appropriate synthesis methods for 1-,4-, 5- and 8- substituted pentacenes is more challenging. For example, the synthesis of tetramethyl pentaquinone following commonly known procedures (see e.g. Chem. Comm, 2009, 3059-3061) leads to a mixture of products where the majority is impurities and thus requires multiple purification steps and results in low yields.

[0040] Thus, in a further aspect of the present invention, an improved and simplified method of synthesizing the above-defined pentacene derivatives is provided, which provides excellent yields: [0041] In general, the synthesis method comprises reacting the compound according to General Formula (V) with the substituted metal acetylide according to General Formula (VI), and dehydrating the resulting product:

(V) (VI), [0042] wherein M is a metal, preferably lithium; wherein R1 to R8 are independently selected from a hydrogen atom, a fluorine atom and an alkyl group having 1 to 4 carbon atoms; and wherein Ra is represented by following General Formula (II):

(II) with R9 and R11 being independently selected from an alkyl group having 1 to 4 carbon atoms; and R10 being selected from any of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 3 carbon atoms.

[0043] Preferably, the compound according to General Formula (V) is being synthesized by reacting either 1,4-benzoquione or a compound according to General Formula (IV) with the compound according to General Formula (III):

wherein X represents a halogen atom, preferably a bromine atom.

[0044] It is preferable that the substituents R2, R3, R6 and R7 in the above General Formulae (III), (IV) and (V) are each a hydrogen atom.

[0045] The compounds according to General Formulae (III), (IV) and (V) may be synthesized according to or in analogy to methods known to the skilled artisan.

[0046] Exemplary synthesis methods for compounds according to General Formula (III) are shown in the following:

[0047] An exemplary method for the synthesis of a compound according to General Formula (IV) is shown in the following:

[0048] An exemplary synthetic route, wherein 1,4-benzoquinone is reacted with a compound falling under General Formula (III) and the product is alkylated with a substituted metal acetylide and dehydrated is shown in the following:

[0049] An exemplary synthetic route, wherein a compound according to General Formula (IV) is reacted with a compound falling under General Formula (III) and the product is alkylated with a substituted metal acetylide and dehydrated is shown in the following:

Synthesis of 1.4-dihvdroxv-5.8-dimethvlanthracene-9.10-dione

[0050] Aluminum chloride (570 g, 4.2614 mol) and sodium chloride (133 g, 2.2720 mol) were taken in a 5000 ml 3-necked flask under N2 atmosphere. The mixture was heated up to 140°C till the mixture was melted into stirrable solution. 4,7-Dimethylisobenzofuran-1,3-dione (50 g, 0.2840 mol) was added into the above solution in portion for an hour. Note, during each addition huge white fumes were seen. Hydroquinone (31.27 g, 0.2840 mol) was added into the reaction mixture in portion slowly. After completion of addition, the temperature was raised to 180°C and maintained for 48 h. The progress of reaction was monitored by TLC and LCMS. The reaction mixture was cooled down to 130°C and 2N HCI (1000 ml) solution was added in drops. Huge white fumes were liberated and quenching took 6 to 8 h. The reaction mixture became rock-hard solid. It was broken into pieces using excess of 2N HCI (~ 8 I). The above mixture was repeatedly extracted with DCM (2 I * 15). Likewise another 50 g batch was performed separately and work up was combined. The organic layer was dried over sodium sulphate and concentrated to get 190 g of product as orange colour solid with 62 % purity (major isomer) by LCMS. The crude was purified by column chromatography using silica gel (60-120 mesh) and DCM/Hexane as eluent. The solid was then crystallized using DCM/hexane (1:10 ratio) repeatedly for several time to obtain 98 g of product 99.3 % HPLC purity (64 % yield).

[0051] 1H-NMR (400 MHz, CDCI3): δ [ppm] 2.47 (s, 6H), 7.30 (s, 2H), 8.08 (s, 2H), 12.96 (s, 2H).

[0052] 13C-NMR (100 MHz, CDCI3): δ [ppm] 20.35, 112.90, 127.94, 129.08, 131.37, 144.72, 157.57, 187.21.

Synthesis of 5.8-dimethvlanthracene-1.4-dione

[0053] In a 500 ml three neck round bottom flask 1,4-dihydroxy-5,8-dimethylanthracene-9,10-dione (5.5 g, 0.0205 mol) was taken in 110 ml methanol. The reaction mixture was cooled to 15 °C then sodium borohydride (7.8 g, 0.2502 mol) was added in portion by controlling temperature <20°C. During the addition of sodium borohydride vigorous effervescence observed. The reaction mixture was stirred at room temperature for 16 h and the progress of reaction was monitored by TLC and LC-MS analysis. The reaction mixture was cooled to 5°C and quenched by adding 6N HCI (~55 ml) slowly to adjust the pH to ~3, an orange red color solid formation was observed. The above mixture was diluted with water (250 ml) and stirring continued for 3 h. The precipitated solid was filtered, washed with water (100 ml χ 2) and dried under vacuum for 4 h to obtain 5.6 g of 5,8-dimethylanthracene-1,4-dione as yellowish red colour solid with 84 % LCMS purity. The crude was purified by neutral alumina column chromatography using hexane/DCM as eluent. The product was further purified by recrystallisation from EtOAc/Hep to get 1.55g, 99.93% HPLC (32% yield). 1H NMR (400 MHz, CDCI3): δ [ppm] 2.50 (s, 6H), 7.05 (s, 2H), 7.81 (s, 2H), 8.50 (s, 2H).

Synthesis of 1,4,8,11-tetramethvlpentacene-6,13-dione

[0054] In a 1L round bottom flask fitted with a condenser 5,8-dimethylanthracene-1,4-dione (5.0 g, 21.16 mmol) and 2,3-bis(bromomethyl)-1,4-dimethylbenzene (6.17 g, 21.16 mmol) were taken. Anhydrous DMF (320 ml) was added and stirred, a yellow solution obtained. Potassium iodide (14.05 g, 84.64 mmol) was added as solid and the reaction mixture was heated at 110°C for 20 hr. The reaction was stopped, cool down to RT then to 0°C using ice bath. The cold mixture was then poured with stirring into cold methanol, yellow precipitation formed. The solid was filtered and washed with MeOH, H20 and MeOH gives material 92-93 % HPLC pure. As the solubility of the material is poor in any organic solvent the rest of the impurities could either be removed by sublimation at 190°C (4.6x10‘6 Torr) for 20 h (41 % yield) or by hot filtration from THF/CHCI3 (67 % yield) as 1,4,8,11-tetramethylpentacene-6,13-dione is not soluble in THF/CHCI3 solvent mixture whereas the impurities are highly soluble in THF or CHCI3. Purification by hot filtration: 4.4g of crude sample was suspended in 1:1 mixture of THF/CHCI3 (200ml) and heated at reflux for overnight then filtered hot followed by washing with THF (20 ml). The process is repeated three times giving >99% HPLC pure material. 1H-NMR (600MHz, DMSO-d6, 0.3 mg/ml DMSO-d6): <5= 9.0 (s, 4H), 7.59(s, 4H), 2.83 (s, 12H). 13C-NMR was not possible due to poor solubility.

Synthesis of 6.13-bis(3-(tert-butvl)-4,4-dimethvlpent-1-vn-1-vl)-6.13-dihvdropentacene-6,13-diol

[0055] In an oven dried 100 ml three neck flask fitted with N2 inlet 3-(tert-butyl)-4,4-dimethylpent-1-yne (5.93g, 38.94 mmol) was taken. Anhydrous THF (40ml) was added and cool down to -40°C. To the reaction flask 2M LDA solution (20 ml, 40 mmol) was added dropwise. Initially the red/brownish colour of LDA disappears with addition. The reaction mixture was allowed to warm to room temperature and stirred for 1 hr at RT. In a separate 1L flask, pentaquinone (3.0 g, 9.73 mmol) was taken under N2. Anhydrous THF (160 ml) was added and cool down to -78°C. The lithialated alkyne from above reaction was added dropwise to the pale yellow suspension of pentaquinone with stirring. The reaction mixture was allowed to warm to room temperature without removing cooling bath and stirred at RT for 24 h by which yellowish clear solution was observed. The progress of reaction was monitored by TLC, and LC-MS analysis. The reaction was stopped and quenched with 40 ml 10% aq. HCI solution. Most of the solvent was evaporated under reduced pressure and the residue was diluted with 100 ml EtOAc. The organic layer was separated and the aqueous layer was extracted with

EtOAc (2 x 20 ml). The combined organic layers were washed with water (2 x 100 ml) and brine (2 x 100 ml), dried over MgS04 and evaporated. The crude product was purified by neutral alumina column chromatography using 10% EtOAc/Heptane as eluent followed by recrystallisation from the same solvent (2.04 g, 42 % yield, 99.55 % HPLC). LC-MS confirms the m/z 612 (M+). 1H-NMR (600MHz, THF-d8): <5= 8.67 (s, 4H), 7.92 (m, 4H), 7.52 (m, 4H), 3.25 (s, 2H), 1.98 (s, 2H), 1.12 (s, 36H).

Synthesis of 6.13-bis(3-(tert-butvl)-3-methoxv-4.4-dimethvlpent-1-vn-1-vD-1.4.8.11-tetramethvl-6,13-dihvdropentacene-6.13-diol

[0056] 1H-NMR (600MHz, THF-d8): δ= 9.46 (s, 4H), 7.10 (s, 4H), 4.05 (s, 6H), 3.27 (s, 2H), 2.6 (s, 12H), 1.14 (s, 36H).

Synthesis of 6.13-bis(3-(tert-butvn-4.4-dimethvlpent-1-vn-1-vhpentacene

[0057] To a THF (50 ml) solution of 6,13-bis(3-(tert-butyl)-4,4-dimethylpent-1-yn-1-yl)-6,13-dihydropentacene-6,13-diol (1.99 g, 3.24 mmol) was added 3M HCI solution (13 ml) of SnCh (2.46 g, 12.97 mmol) dropwise at RT while protecting the flask from light. With addition a drop of SnCh/HCI into the reaction flask the colour of the solution changed to dark blue/purple. The reaction mixture was stirred for 16 hr before solvent was evaporated to dryness. The blue solid was dissolved in dichloromethane(70ml) and washed with H20( 3 x 70 ml), dried over MgSCL and filtered. The product is further purified by repeated precipitation from MeOH (1.6 g, 65 % yield, 99.57 % HPLC). LC- MS confirms the m/z 578 (M+). 1H-NMR (600MHz, THF-d8): δ- 8.66 (s, 4H), 7.90 (m, 4H), 7.45 (m, 4H), 2.04(s, 2H), 1.48 (s, 36H).

Synthesis of 6,13-bisi3-(tert-butvl)-3-methoxv-4,4-dimethvlpent-1-vn-1-vl)-1.4.8.11-tetramethvloentacene

[0058] 1H-NMR (600MHz, THF-d8): δ= 9.48 (s, 4H), 7.18 (s, 4H), 4.01 (s, 6H), 2.81(s, 12H), 1.50 (s, 36H).

[0059] Substituted metal acetylides in accordance with General Formula (VI) may be prepared in analogy to the following exemplary reaction schemes leading to the alkyne precursors, which may be subsequently metalated according to procedures commonly known in the art (e.g. lithiation with BuLi):

Synthesis of 3-(tert-butvl)-4l4-dimelhvM.()rimfi)hu|si|uhnpn,,1_un ^n|

[0060] To a solution of trimethylsilylacetylene (4.48 g, 45.70 mmol) in THF (30 ml) cooled down at -78°C, a 2.5 M n-butyllithium in hexanes (18.28 ml, 45.70 mmol) was added dropwise. The solution was allowed to warm up to room temperature and stirred for 30 min before a solution of di-terf-butyl ketone (5.0 g, 35.15 mmol) in THF (10 ml) was added slowly at -78°C. The reaction was stirred at -78oC for 1 hr and allowed to warm to room temperature over a period of 16 h. It was then quenched with a saturated ammonium chloride solution at 0°C. The aqueous layer was extracted with diethyl ether (4 x 25 ml). The combined organic layers were washed with brine, dried over MgS04, filtered and concentrated under reduced pressure. The crude residue (7.8 g, 92.3 % yield, low melting solid) obtained was used as such for the next step. 1H-NMR (600MHz, CDCI3, TMS): <5= 1.78 (s, br, 1H), 1.17 (s, 18H), 0.17 (s, 9H).

Synthesis of 3-(tert-butvl)-4.4-dimethvlpent-1-vn-3-ol

[0061] To a solution of 3-(tert-butyl)-4,4-dimethyl-1-(trimethylsilyl)pent-1-yn-3-ol (17.76 g, 76.86 mmol) in diethyl ether (50 ml) was added dropwise 1.0M THF solution of TBAF(106 ml, 110.79 mmol) at 0°C during which white precipitation formed. The reaction mixture was allowed to stir at 0°C for 15 min then allowed to warm to room temp and stirred of 2 h (pale yellowish solution observed). The solvent was evaporated and the yellowish liquid was diluted with 20 ml of pentane. It was then passed through a pad of fluorosil/silica and washed with 300 ml of pentane. It was then washed with a saturated solution of NH4CI, water and brine, dried over MgS04. Gentle evaporation of solvent under reduced pressure to give pure product (12.0 g, quantitative yield) which was stored at <4°C. 1H-NMR (600MHz, CDCh, TMS): <5= 2.44 (s, 1H), 1.18 (s, 18H).

Synthesis of 1-bromo-3-(tert-butvl)-4.4-dimethvlpenta-1.2-diene

[0062] A 100 ml round bottom flask was charged with copper (I) bromide (5.11 g, 35.65 mmol) and copper powder (1.42 g, 22.34 mmol). Hydrobromic acid (48 %, 15 ml) was added dropwise and stirred for 10 min. A pale yellow solution was obtained. To this mixture a pentane solution (10 ml) of 3-(tert-butyl)-4,4-dimethylpent-1-yn-3-ol (4.0 g, 23.77 mmol) was added dropwise and stirred at 40°C for 16 h. The colour of the solution changed to brownish. The biphasic mixture was transferred to a separatory funnel and the organic layer was collected. The aqueous layer was extracted with pentane (3 x 20 ml) and the combined organic layers were washed with aqueous concentrated hydrobromic acid (3x5 ml) and water (2 x 10 ml), dried over MgSC>4 and eluted through a plug of silica, which afforded allenyl bromide (4.04 g, 73.58 % yield) after evaporation of solvent. The pure allene was stored in the dark at <4°C. 1H-NMR (600MHz, CDCIs, TMS): <5= 5.88 (s, 1H), 1.23 (s, 18H). GC-MS; m/z found 151/152 (M+-Br).

Synthesis of 3-(tert-butvD-4,4-dimethvlpent-1-vne

[0063] A 500ml four neck round bottom flask equipped with a dropping funnel, mechanical stirrer and thermometer was charged with 2M THF solution of UAIH4 (71.37 ml, 142.75 mmol) under nitrogen atmosphere. A THF (50 ml) solution of 1-bromo-3-(tert-butyl)-4,4-dimethylpenta-1,2-diene (22.0 g, 95.16 mmol) was added to the reaction flux dropwise at 0°C. The reaction mixture was then allowed to warm to room temperature and stirred for 16 h. It was quenched with careful dropwise addition of saturated NH4CI (50 ml) solution at 0°C and temperature was maintained <10°C. Most of the solvent was evaporated under reduced pressure. It was then diluted with 100 ml of pentane and washed with brine, water, dried over MgSCX The resultant pale yellowish liquid was passed through a pad of fluorosil/celite plug and washed with pentane. Evaporation of solvent gives pure alkyne (11.3 g, 78 % yield). 1H-NMR (600MHz, CDCb, TMS): <5= 2.12 (d, 2.6Hz, 1H), 2.10 (d, 2.6Hz, 1H), 1.17 (s, 18H). It contains 1.5 wt.-% allene isomers, the material was used without further purification.

Synthesis of (3-(tert-butvl)-3-methoxv-4.4-dimethvlpent-1-vn-1-yl)trimethvlsilane

[0064] To a solution of trimethylsilylacetylene (22.4 g, 228.5 mmol) in THF (150 ml) cooled down at -78°C, a 2.5M n-butyllithium in hexanes (91.4 ml, 228.5 mmol) was added dropwise. The solution was allowed to warm up to room temperature and stirred for 30 min before a solution of di-te/f-butyl ketone (25.0 g, 175.75 mmol) in THF (50 ml) was added slowly at -78°C. The reaction was stirred at -78°C for 1 h and allowed to warm to room temperature over a period of 16 h. It was then cool down again to -78°C and Mel (124.7 g, 878.75 mmol) was added dropwise before allow to warm to room temperature and stirred for overnight. The reaction was quenched with a saturated ammonium chloride solution at 0°C. The aqueous layer was extracted with diethyl ether (2 x 100 ml). The combined organic layers were washed with brine, dried over MgSC>4, filtered and concentrated under reduced pressure. (40 g, 89.5% yield). 1H-NMR (600MHz, CDCI3, TMS): <5= 3.41 (s, 3H), 1.19 (s, 18H), 0.17 (s, 9H).

Synthesis of 3-(tert-butvl)-3-methoxv-4.4-dimethvlpent-1-vne

[0065] To a THF (200ml) solution of (3-(tert-butyl)-3-methoxy-4,4-dimethylpent-1-yn-1-yl)trimethylsilane (40.0 g, 157.35 mmol) was added dropwise a MeOH (200 ml) solution of K2CO3 (65.2 g, 472 mmol). The reaction mixture was allowed to stir for 16 h at RT. The solvent was evaporated and the yellowish liquid was diluted with 200 ml of pentane. It was then washed with a saturated solution of NH4CI, water and brine, dried over MgS04. The crude product was purified by grace column using 5% EtOAc/Heptane as eluent (22 g, 76.9% yield). 1H-NMR (600MHz, CDCU, TMS): δ= 3.43 (s, 3H), 2.12 (s, 1H), 1.18 (s, 18H).

ORGANIC THIN FILMS AND THEIR APPLICATIONS

[0066] In a further embodiment, the present invention relates to organic thin films comprising the above-described pentacene derivatives.

[0067] For the preparation of such organic thin films, the compounds according to the present invention may be used on their own or in combination with a polymer to form an organic material blend.

[0068] The organic thin films may be fabricated by depositing the pentacene derivatives according to the first embodiment of the present invention on a substrate according to conventional methods known in the art, or alternatively dissolving said compounds in an organic solvent (optionally together with the polymer) and then coating the same at room temperature according to a solution process. After the deposition or coating process, a heating treatment may be performed to further enhance the densification and uniformity of the thin film. The method of film deposition may include thermal deposition, vacuum deposition, laser deposition, screen printing, printing, imprinting, spin casting, dipping, inkjetting, roll coating, flow coating, drop casting, spray coating, and/or roll printing, for example. Preferred solution deposition techniques include spin coating and inkjet printing.

[0069] The organic solvent is not particularly limited and may include an aliphatic hydrocarbon (e.g. hexane or heptane), a haloalkane (e.g. chloroform), an aromatic hydrocarbon (e.g. toluene, pyridine, tetralin, quinoline, anisole, mesitylene, or xylene), a ketone (e.g. methyl isobutyl ketone, 1-methyl-2-pyrrolidinone, cyclohexanone, or acetone), an ether (e.g. tetrahydrofuran or isopropyl ether), an acetate (e.g. ethyl acetate, butyl acetate, or propylene glycol methyl ether acetate), an alcohol (e.g. isopropyl alcohol or butanol), an amide (e.g. dimethyl acetamide or dimethyl formamide), a silicone, and a mixture thereof. The type and amount of the solvent relative to the pentacene derivative may be appropriately selected and determined by a person of ordinary skill in the art.

[0070] The thickness of the organic thin films is not particularly limited and may be adjusted appropriately by the skilled artisan depending on their application. Usually, thicknesses of 1 pm or less are used, and for use in OFETs or OLEDs, the layer thickness is preferably 500 nm or less.

[0071] If the compounds according to the present invention are used in combination with a polymer to form an organic material blend, the polymer may be a polymeric binder as conventionally used in the art (see WO 2012/076092 A1 or WO 2005/055248 A2, for example). In a preferred embodiment, the polymer used to form the blend has a dielectric constant at 1000 Hz of less than 3.4, preferably less than 3.3. The dielectric constant of the organic binders can be measured using any standard method known to those skilled in the art, preferably according to the ASTM D150 test method.

[0072] Advantageously, the organic thin film of the present invention has a high carrier mobility. Mobility is preferably 1x10_3cm2/Vs or more, more preferably 1χ10-2 cm2/Vs or more, and even more preferably 1*10-1 cm2/V s or more.

[0073] The organic thin films according to the present invention may be used in electronic devices and components as charge transport, semiconducting, electrically conducting, photoconducting or light emitting material, preferably as semiconducting material.

[0074] Examples of electronic devices and components including the organic thin film as a carrier transport layer may include a transistor, an organic light emitting diode (OLED), a photovoltaic device, a solar cell, a laser device, a memory, and/or a sensor, and the organic thin film may be applied to each device according to a conventional process commonly known in the art.

[0075] In a preferred embodiment, the organic thin films according to the present invention are used as semiconducting layers in organic thin film transistors (OTFT). The organic thin-film transistor can be used for various displays, e.g., liquid crystal display, dispersed liquid crystal display, electrophoretic display, particle rotating display, electrochromic display, organic light-emitting display, and electronic paper. The transistor and thin-film transistor are used for various devices, e.g., signal driving circuit, memory circuit, pixel switching transistor, signal processing circuit and so forth in these displays.

[0076] An exemplary configuration of an OTFT is shown in Fig. 1, illustrating the general architecture of a bottom-gate OTFT in which the organic thin film according to the present invention may be preferably used. Herein, a gate electrode 72 is deposited on a substrate 10. An insulating layer 77 of dielectric material is deposited over the gate electrode 72 and source and drain electrodes 13, 14 are deposited over the insulating layer 77 of dielectric material. The source and drain electrodes 13, 14 are spaced apart to define a channel region therebetween located over the gate electrode 72. The organic semiconductor material 75 is deposited in the channel region for connecting the source and drain electrodes 13, 14. The organic semiconductor material 75 may extend at least partially over the source and drain electrodes 13, 14.

[0077] In a preferred alternative embodiment, the organic thin film according to the present invention is used in an organic thin film transistor having a top-gate configuration, i.e. wherein the gate electrode is provided at the top of an organic thin film transistor. In such an architecture, source and drain electrodes are deposited on a substrate and spaced apart to define a channel region there between. A layer of an organic semiconductor material is deposited in the channel region to connect the source and drain electrodes and may extend at least partially over the source and drain electrodes. An insulating layer of dielectric material is deposited over the organic semiconductor material and may also extend at least partially over the source and drain electrodes. A gate electrode is deposited over the insulating layer and located over the channel region.

[0078] In general, organic thin film transistors may be fabricated on rigid or flexible substrates. Rigid substrates may be selected from glass or silicon and flexible substrates may comprise thin glass or plastics such as poly(ethylene-terephthalate) (PET), poly(ethylene-naphthalate) (PEN), polycarbonate and polyimide, for example.

[0079] The gate electrode can be selected from a wide range of conducting materials for example a metal (e.g. gold) or metal compound (e.g. indium tin oxide). Alternatively, conductive polymers may be deposited as the gate electrode. Such conductive polymers may be deposited from solution using, for example, spin coating or ink jet printing techniques and other solution deposition techniques discussed above.

[0080] The insulating layer comprises a dielectric material selected from insulating materials having a high resistivity. The dielectric constant, k, of the dielectric material is typically around 2-3 although materials with a high value of k are desirable because the capacitance that is achievable for an OTFT is directly proportional to k, and the drain current ID is directly proportional to the capacitance. Thus, in order to achieve high drain currents with low operational voltages, OTFTs with thin dielectric layers in the channel region are preferred. The dielectric material may be organic or inorganic. Preferred inorganic materials include S1O2, SiNx and spin-on-glass (SOG). Preferred organic materials are generally polymers and include insulating polymers such as poly vinylalcohol (PVA), polyvinylpyrrolidine (PVP), acrylates such as polymethylmethacrylate (PMMA) and benzocyclobutanes (BCBs), for example. The insulating layer may be formed from a blend of materials or comprise a multi-layered structure.

[0081] Fig. 2 shows a pixel comprising an organic thin film transistor 100 and an adjacent organic light-emitting device (OLED) 102 fabricated on a common substrate 104. The OTFT 100 comprises gate electrode 106, dielectric layer 108, source and drain electrodes 110 and 112 respectively, and OSC layer 114. The OLED 102 comprises anode 116, cathode 118 and an electroluminescent layer 120 provided between the anode 116 and cathode 118. Further layers may be located between the anode 116 and cathode 118, such as charge transporting, charge injecting or charge blocking layers. In the embodiment of Fig. 2, the layer of cathode material 118 extends across both the OTFT 100 and the OLED 102, and an insulating layer 122 is provided to electrically isolate the cathode layer 118 from the OSC layer 114. The active areas of the OTFT 100 and the OLED 102 are defined by a common bank material formed by depositing a layer of photoresist 124 on substrate 104 and patterning it to define OTFT 100 and OLED 102 areas on the substrate.

[0082] In Fig. 2, the drain electrode 112 is directly connected to the anode 116 of the organic light-emitting device 102 for switching the organic light-emitting device 102 between emitting and non-emitting states.

[0083] In an alternative arrangement illustrated in Fig. 3, an organic thin film transistor 200 may be fabricated in a stacked relationship to an organic light-emitting device 202. In such an embodiment, the organic thin film transistor 202 is built up as described above in either a top or bottom gate configuration. As with the embodiment of Fig. 2, the active areas of the OTFT 200 and OLED 202 are defined by a patterned layer of photoresist 124, however in this stacked arrangement, there are two separate bank layers 124—one for the OLED 202 and one for the OTFT 200. A planarisation layer 204 (also known as a passivation layer) is deposited over the OTFT 200. Exemplary passivation layers 204 include BCBs and parylenes. The organic light-emitting device 202 is fabricated over the passivation layer 204 and the anode 116 of the organic light-emitting device 202 is electrically connected to the drain electrode 112 of the OTFT 200 by a conductive via 206 passing through passivation layer 204 and bank layer 124.

[0084] It will be appreciated that pixel circuits comprising an OTFT and an optically active area (e.g. light emitting or light sensing area) may comprise further elements. In particular, the OLED pixel circuits of Figures 2 and 3 will typically comprise least one further transistor in addition to the driving transistor shown, and at least one capacitor. It will be appreciated that the organic light-emitting devices described herein may be top or bottom-emitting devices. That is, the devices may emit light through either the anode or cathode side of the device. In a transparent device, both the anode and cathode are transparent. It will be appreciated that a transparent cathode device need not have a transparent anode (unless, of course, a fully transparent device is desired), and so the transparent anode used for bottom-emitting devices may be replaced or supplemented with a layer of reflective material such as a layer of aluminium.

[0085] Transparent cathodes are particularly advantageous for active matrix devices because emission through a transparent anode in such devices may be at least partially blocked by OTFT drive circuitry located underneath the emissive pixels as can be seen from the embodiment illustrated in Fig. 3.

[0086] Other layers may be included in the device architecture. For example, in addition to providing a self assembled monolayer (SAM) on the gate, source or drain electrodes one may be provided on the, substrate, insulating layer and organic semiconductor material to promote crystallinity, reduce contact resistance, repair surface characteristics and promote adhesion where required. In particular, the dielectric surface in the channel region may be provided with a monolayer comprising a binding region and an organic region to improve device performance, e.g. by improving the organic semiconductor's morphology (in particular polymer alignment and crystallinity) and covering charge traps, in particular for a high k dielectric surface. Exemplary materials for such a monolayer include chloro- or alkoxy-silanes with long alkyl chains, e.g. octadecyltrichlorosilane.

EXAMPLES

[0087] Quantum chemical calculations were performed with the hybrid density functional theory (DFT) method using LC-wPBE/6-31G* according to methods known in the art in order to determine the carrier transport properties of compound according to the present invention. In particular, the hole mobility, the transfer integral and the reorganization energy of compound (1) has been calculated and compared to 6,13-bis[(triisopropylsilyl)ethynyl] pentacene (TIPS-pentacene), the structural formula of which is shown in the following:

[0088] The results of the calculations are shown in Figures 4A, 4B and 4C.

[0089] Reorganization energy (λ) is an important molecular factor that may affect charge transport properties of OSC materials. Carrier transport in organic solids is often described by the hopping model, where the high mobility, i.e. rapid exchange of carriers between molecules can be realized by a small energy, λ (energy consumption during carrier exchange at the molecular level). For p-type OSC materials largely tt-extended compounds tend to have smaller (λ for hole) values in general, because of the effective delocalization of hole in the radical cation state, which reduces structural deformation during carrier transport. The smaller the Ah value, materials show better transport properties.

[0090] As is demonstrated by Fig. 4A, the pentacene derivative according to the present invention exhibits superior hole mobility (3.867) when compared to TIPS-pentacene (0.855). Moreover, an improved transfer integral (0.0992) and a favourably low reorganization energy (0.108) is observed in comparison with TIPS-pentacene (0.0941 and 0.138, respectively), as is shown in Fig. 4B and 4C.

[0091] Stacking structures of TIPS-pentacene and compound (1) as optimized by LC-wPBE/6-31G* are depicted in comparison in Figures 5A and 5B.

[0092] Further quantum chemical calculations were performed with the hybrid density functional theory (DFT) method using B3LYP and the 6-31G* (5d) basis set according to methods known in the art in order to determine the theoretical hole mobility of further derivatives according to the present invention. In particular, the hole mobility of compounds (13), (14), (22), and (58) have been calculated in accordance with procedures described in the literature (see e.g. J. Phys. Chem. A, 2003, 107, 5241-5251) and compared to TIPS-pentacene.

[0093] As is demonstrated in Fig. 6, the pentacene derivatives according to the present invention exhibit a remarkably higher hole mobility than TIPS-pentacene. The comparison between the charge carrier mobility performance of compounds (22) and (58) further demonstrates the enhancement in hole mobility upon replacing the methyl groups at the pentacene scaffold with fluorine atoms.

[0094] Hence, it is demonstrated that the pentacene derivatives of the present invention are suitable candidates for organic semiconductor applications having favourable ττ-π stacking and excellent charge carrier mobility properties, and at the same time exhibit a good solubility in typical organic solvents so they may be applied by a large variety of solution deposition techniques.

[0095] Once given the above disclosure, many other features, modifications, and improvements will become apparent to the skilled artisan.

Claims (15)

1. Pentacene derivative represented by the following General Formula (I):

(I) wherein R1 to R8 are independently selected from a hydrogen atom, a fluorine atom and an alkyl group having 1 to 4 carbon atoms; and wherein Ra is a solubilising group represented by the following General Formula

(II): (II) with R9 and R11 being independently selected from an alkyl group having 1 to 4 carbon atoms; and R10 being selected from any of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 3 carbon atoms.

2. Pentacene derivative according to claim 1, wherein R9 and R11 are independently selected from a methyl group, an ethyl group, an isopropyl group, or a tert-butyl group; and R10 is selected from any of a hydrogen atom, a methyl group, an ethyl group, an isopropyl group, a tert-butyl group, and an alkoxy group having 1 to 3 carbon atoms.

3. Pentacene derivative according to any of claims 1 or 2, wherein R10 is selected from any of a hydrogen atom, a methyl group, an ethyl group, an isopropyl group, or a tert-butyl group, and R9 and R11 are selected from an isopropyl group or a tert-butyl group; or wherein R10 is an alkoxy group having 1 to 3 carbon atoms, and R9 and R11 are selected from a methyl group, an ethyl group, an isopropyl group, or a tert-butyl group.

4. Pentacene derivative according to any of claims 1 to 3, wherein R9 and R11 are identical.

5. Pentacene derivative according to any of claims 1 to 4, wherein R11 is a methoxy group.

6. Pentacene derivative according to any of claims 1 to 5, wherein all of R2, R3, R6 and R7 are hydrogen atoms.

7. Pentacene derivative according to any of claims 1 to 6, wherein all of R1, R4, R5 and R8 are fluorine atoms or wherein all of R1, R4, R5 and R8are methyl groups.

8. Pentacene derivative according to any of claims 1 to 6, wherein R1 and R8 each represent a fluorine atom and R4 and R5 each represent a hydrogen atom.

9. Pentacene derivative according to any of claims 1 to 6, wherein R1 and R8 each represent a methyl group and R4 and R5 each represent a hydrogen atom.

10. Pentacene derivative according to any of claims 1 to 6, wherein R1 and R8 each represent a fluorine atom and R4 and R5 each represent a methyl group.

11. Pentacene derivative according to any of claims 1 to 10, wherein Ra is selected from any of the structural formulae (1-1) to (1-12):

12. Method of synthesizing the pentacene derivative according to any of claims 1 to 11, comprising reacting the compound according to General Formula (V) with the compound according to General Formula (VI), and dehydrating the resulting product:

wherein M is a metal, preferably lithium; wherein R1 to R8 are independently selected from a hydrogen atom, a fluorine atom and an alkyl group having 1 to 4 carbon atoms; and wherein Ra is represented by following General Formula (II):

(II) with R9 and R11 being independently selected from an alkyl group having 1 to 4 carbon atoms; and R10 being selected from any of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 3 carbon atoms.

13. Method according to claim 12, further comprising the step of reacting either 1,4-benzoquione or a compound according to General Formula (IV) with the compound according to General Formula (III) to form the compound according to General Formula (V):

(IV)

(ill) wherein R1 to R8 are independently selected from a hydrogen atom, a fluorine atom and an alkyl group having 1 to 4 carbon atoms; and wherein X represents a halogen atom, preferably a bromine atom.

14. Organic thin film comprising the pentacene derivative according to any of claims 1 to 11, optionally further comprising a polymer.

15. An electronic device or component comprising an organic thin film according to claim 14.