WO2016071140A1

WO2016071140A1 - Phenacene compounds for organic electronics

Info

Publication number: WO2016071140A1
Application number: PCT/EP2015/074756
Authority: WO
Inventors: Chongjun JIAO; Thomas Weitz; Michael EUSTACHI; Sweemeng Ang; Fabien Nekelson
Original assignee: Basf Se
Priority date: 2014-11-04
Filing date: 2015-10-26
Publication date: 2016-05-12
Also published as: TW201623311A

Abstract

Phenacene compounds of formula (I) wherein R¹ and R² are independently of each other a linear or branched C_1-20 alkyl group.

Description

Phenacene compounds for organic electronics

Description

The invention relates to phenacene compounds and their use.

Organic semiconducting materials can be used in electronic devices such as organic photovoltaic (OPV) cells, organic field-effect transistors (OFETs) and organic light emitting diodes (OLEDs).

It is desirable that the organic semiconducting materials are compatible with liquid processing techniques such as spin coating, solution casting or printing. Liquid processing techniques are convenient from the point of processability, and can also be applied to plastic substrates. Thus, organic semiconducting materials which are compatible with liquid processing techniques allow the production of low cost, light weight and, optionally also flexible, electronic devices, which is a clear advantage of these organic semiconducting materials compared to inorganic semiconducting materials.

Furthermore, it is desirable that the organic semiconducting materials are stable, in particular towards oxidation.

When used in organic field-effect transistors (OFETs), the organic semiconducting materials should show a high charge carrier mobility and a high on/off ratio.

The use of organic semiconducting materials in electronic devices, in particular in organic field effect transistors (OFETs) is known in the art.

Okamoto, K.; Kawasaki, N.; Kaji, Y.; Kubozono, Y.; Fujiwara, A.; Yamaji, M. J. Am. Chem. Soc. 2008, 130, 10470-10471 and Kawasaki, N.; Kubozono, Y.; Okamoto, H.; Fujiwara, A.; Yamaji, M. Appl. Phys. Lett. 2009, 94, 043310 describe picene

for vacuum-deposited OFETs with a charge carrier mobility approaching 3 cm² V-¹S^"1.

Okamoto, K.; Eguchi R.; Hamao S.; Gotoh K.; Sakai Y.; Izumi M.; Takaguchi Y.; Gohda S.; Kubozono Y. Sci. Rep. 2014, 4, 5330 describe [8]phenacene.

for vacuum deposited OFETs with a charge carrier mobility of 16.4 cm²V-¹ s^_1.

JP2009/063846 discloses alkylated picene for solution-based OFETs with a charge carrier mobility of up to 2 cm²V-¹ S^"1.

S. Shinamura et al., K. J. Am. Chem. Soc. 201 1 , 133, 5024 - 5035 disclose linear- and angular- shaped naphthodithiophenes of the following formulae:

wherein R is H, n-C8Hi₇ or phenyl,

for vacuum-deposited OFETs with a charge carrier mobility approaching 1.5 cm² V^-1 s^_1.

US 201 1/0210319 describes organic field effect transistors (OFETs) containing the following π- extended S-containing heteroarene compounds.

These OFETs show the following charge carrier mobilities: 1 .2 (compound 1 ), 1 .8 (compound 2), 2.0 (compound 3), 1 .7 (compound 4) cm² V^-1 s^_1, and the following on-off ratios: 2 x 10⁶ (compound 1 ), 3 x 10⁶ (compound 2), 4 x 10⁶ (compound 3) and 3 x 10⁶ (compound 4).

J. Gao et al., Adv. Mater. 2007, 19, 3008 -301 1 disclose dibenzothienodithioph

for OFETs with a charge carrier mobility above 0.5 cm² V^"1 s^_1 and an on/off ratio greater than 10⁶.

K. Xiao et al., J. Am. Chem. Soc. 2005, 127, 13281 -13286 disclose pentathienoacene

with a charge carrier mobility of 0.045 cm² V^-1 s^_1 and an on/off ratio of 10³ for vacuum-deposited OFETs.

Miyata, Y.; Yoshikawa, E.; Minari, T.; Tsukagoshi, K.; Yamaguchi, S. J. Mater. Chem. 2012, 22, 7715-7717 describes OFETs comprising the following compound

as semiconductor. One of the OFETs shows a charge carrier mobility of 3.1 cm V^-1 s^_1 and an on/off ratio of 10⁵.

Kurihara, N.; Yao, A.; Sunagawa, M.; Ikeda, Y.; Terai, K.; Kondo H.; Saito M.; Ikeda, H.; Naka- mura, H.; J. J. Appl. Phys. 2013, 52, 05DC1 1 reports dioctyl-bis(benzothieno)naphthalene

With a charge carrier mobility of 15.6 cm²V-¹ s^_1 and an on/off ratio of 10⁵ for vacuum deposited OFET.

J. Wang et al., Chem. Mater. 2009, 21 , 2595 - 2597, describe the following small molecule:

for vacuum-deposited OFET with a charge carrier mobility up to 0.4 cm² V^-1 s^_1. Accordingly, given potential applications in inexpensive and large-area organic electronics that can be produced by high-throughput reel-to-reel manufacture, the art desires new organic p- type semiconducting compounds, especially those possessing desirable properties such as air stability, high charge transport efficiency, and good solubility in common organic solvents. WO 2013/168048 A1 discloses phenacene compounds of the general formula

wherein

one of groups a, b and c is X and the other two groups are C-R¹ and C-R², respectively, one of groups d, e and f is X and the other two groups are C-R⁵ and C-R⁶, respectively, wherein X are, independently of each other, selected from the group consisting of NH, O, S and Se, preferably selected from the group consisting of O, S and Se, more preferably selected from the group consisting of O and S, and particular preferably are S,

R¹ - R¹⁰ are independently of each other H, halogene, -CN, -NO2 or a linear or branched, saturated or unsaturated C1-C40 hydrocarbon residue, which can be substituted 1 - to 5-fold with halogene (F, CI, Br, I), -OR^a, -NR^a2, -CN and/or -NO2, and wherein one or more Chb-groups can be replaced by -0-, -S-, -NR^b-, -OC(O)- or -C(O)-, and wherein R^a and R^b are independently of each other H, C1-C30 alkyl, C2-C30 alkenyl, C2-C30 alkynyl, C1-C30 haloalkyl, C2-C30 haloalkenyl, C2-C30 haloalkynyl or C2-C30 acyl.

Preferably, R¹, R², R⁵ and R⁶ are selected from the group consisting of H, halogen (F, CI, Br, I), and a C1-20 alkyl group.

Preferably, R³, R⁴ are selected from the group consisting of H, halogen (F, CI, Br, I), and a C1-20 alkyl group. Preferably, R⁷, R⁸, R⁹, R¹⁰ are selected from the group consisting of H, halogen atom and C1-20 alkyl groups.

However, expressly disclosed are only compounds of the formula:

wherein R¹, R⁵ are alkyl, in particular n-tetradecyl.

In light of the foregoing, it is an object of the present invention to provide compounds that can be utilized as organic semiconductors and related materials, compositions, composites, and/or devices that can address various deficiencies and shortcomings of the state-of-the-art, including those outlined above.

The object is solved by phenacene compounds of formula I

wherein

R¹ and R² are independently of each other a linear or branched C1-20 alkyl group.

It has been found that the phenacene compounds of the present invention have particular good semiconducting activity. Materials prepared from these compounds have demonstrated unexpected properties. It has been discovered that compounds of the present invention have exceptionally high carrier mobility and/or good current modulation characteristics in field-effect devic- es (e.g., thin-film transistors). In addition, it has been discovered that compounds of the present invention possess certain processing advantages compared to related representative compounds such as better solubility to permit solution-processability and/or good stability at ambient conditions, for example, air stability. Further, the compounds can be embedded with other components for utilization in a variety of semiconductor-based devices.

R¹ and R² can be linear or branched C1-C20 alkyl.

Examples are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec. -butyl, isobutyl, tert. -butyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl, 1 ,1 ,3,3-tetramethylpentyl, n-hexyl, 1 -methylhexyl, 1 ,1 ,3,3,5,5-hexamethylhexyl, n-heptyl, isoheptyl, 1 ,1 ,3,3-tetramethylbutyl, 1 -methylheptyl, 3- methylheptyl, n-octyl, 1 ,1 ,3,3-tetramethylbutyl and 2-ethylhexyl, n-nonyl, decyl, undecyl, do- decyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl and eicosyl.

In a preferred embodiment, R¹ and R² are independently of each other a linear or branched C6- CM alkyl group.

Particularly preferred groups R¹ and R² are selected from the group consisting of n-hexadecyl, n-tetradecyl, n-dodecyl, n-decyl, n-octyl, n-hexyl and 1 -methylpentyl.

In general, R¹ and R² are the same alkyl group. However, R¹ and R² can be different alkyl groups.

Compounds of general formula I can be obtained by the synthetic route shown below. LDA, THF,

0 °C, RT

R= alkyl

Br Br j) LDA, THF Br Br

5 -78 °C,' RT ICI, PCM, _ Br

ii) TMSCI

₀ °C to rt *^" '" ^"' 'PrMgCI, THF,

-78 °C, RT

As the compounds disclosed herein are soluble in common solvents, the present invention can offer processing advantages in fabricating electrical devices such as thin film semiconductors, field-effect devices, organic light emitting diodes (OLEDs), organic photovoltaics, photodetec- tors, capacitors, and sensors. As used herein, a compound can be considered soluble in a sol- vent when at least 1 mg of the compound can be dissolved in 1 ml. of the solvent. Examples of common organic solvents include petroleum ethers; acetonitrile; aromatic hydrocarbons such as benzene, toluene, xylene, and mesitylene; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane, bis(2-methoxyethyl) ether, diethyl ether, di-/sopropyl ether, and f-butyl methyl ether; alcohols such as methanol, ethanol, butanol, and /sopropyl alco- hoi; aliphatic hydrocarbons such as hexanes; acetates such as methyl acetate, ethyl acetate, methyl formate, ethyl formate, isopropyl acetate, and butyl acetate; amides such as dimethyl- formamide and dimethylacetamide; sulfoxides such as dimethylsulfoxide; halogenated aliphatic and aromatic hydrocarbons such as dichloromethane, chloroform, ethylene chloride, chloroben- zene, dichlorobenzene, and trichlorobenzene; and cyclic solvents such as cyclopentanone, cy- clohexanone, and 2-methylpyrrolidone. Examples of common inorganic solvents include water and ionic liquids.

Accordingly, the present invention further provides compositions that include one or more compounds of formula (I) disclosed herein dissolved or dispersed in a liquid medium, for example, an organic solvent, an inorganic solvent, or combinations thereof (e.g., a mixture of organic solvents, inorganic solvents, or organic and inorganic solvents). In some embodiments, the composition can further include one or more additives independently selected from detergents, dis- persants, binding agents, compatibilizing agents, curing agents, initiators, humectants, anti- foaming agents, wetting agents, pH modifiers, biocides, and bactereriostats. For example, sur- factants and/or other polymers (e.g., polystyrene, polyethylene, poly-alpha-methylstyrene, poly- isobutene, polypropylene, polymethylmethacrylate, and the like) can be included as a disper- sant, a binding agent, a compatibilizing agent, and/or an antifoaming agent. In some embodiments, such compositions can include one or more compounds disclosed herein, for example, two or more different compounds of the present invention can be dissolved in an organic solvent to prepare a composition for deposition. In certain embodiments, the composition can include two or more regioisomers. Further, it should be understood that the devices described herein also can comprise one or more compounds of the present invention, for example, two or more regioisomers as described herein. Various deposition techniques, including various solution-processing techniques, have been used in preparing organic electronics. For example, much of the printed electronics technology has focused on inkjet printing, primarily because this technique offers greater control over feature position and multilayer registration. Inkjet printing is a noncontact process, which offers the benefits of not requiring a preformed master (compared to contact printing techniques), as well as digital control of ink ejection, thereby providing drop-on-demand printing. Micro dispensing is another non-contact method of printing. However, contact printing techniques have the key advantage of being well-suited for very fast roll-to-roll processing. Exemplary contact printing techniques include, but are not limited to, screen-printing, gravure printing, offset printing, flexo- graphic printing, lithographic printing, pad printing, and microcontact printing. As used herein, "printing" includes a noncontact process, for example, inkjet printing, micro dispensing, and the like, and a contact process, for example, screen-printing, gravure printing, offset printing, flexo- graphic printing, lithographic printing, pad printing, microcontact printing, and the like. Other solution processing techniques include, for example, spin coating, drop-casting, zone casting, dip coating, blade coating, or spraying. In addition, the deposition step can be carried out by vacuum vapor-deposition.

The present invention, therefore, further provide methods of preparing a semiconductor material. The methods can include preparing a composition that includes one or more compounds of formula (I) disclosed herein dissolved or dispersed in a liquid medium such as a solvent or a mixture of solvents, and depositing the composition on a substrate to provide a semiconductor material (e.g., a thin film semiconductor) that includes one or more compounds of formula (I) disclosed herein. In various embodiments, the liquid medium can be an organic solvent, an inorganic solvent such as water, or combinations thereof. In some embodiments, the composition can further include one or more additives independently selected from viscosity modulators, detergents, dispersants, binding agents, compatibilizing agents, curing agents, initiators, hu- mectants, antifoaming agents, wetting agents, pH modifiers, biocides, and bactereriostats. For example, surfactants and/or polymers (e.g., polystyrene, polyethylene, poly-alpha-methyl- styrene, polyisobutene, polypropylene, polymethylmethacrylate, and the like) can be included as a dispersant, a binding agent, a compatibilizing agent, and/or an antifoaming agent. In some embodiments, the depositing step can be carried out by printing, including inkjet printing and various contact printing techniques (e.g., screen-printing, gravure printing, offset printing, pad printing, lithographic printing, flexographic printing, and microcontact printing). In other embodiments, the depositing step can be carried out by spin coating, drop-casting, zone casting, dip coating, blade coating, or spraying.

Various articles of manufacture including electronic devices, optical devices, and optoelectronic devices such as field effect transistors (e.g., thin film transistors), photovoltaics, organic light emitting diodes (OLEDs), complementary metal oxide semiconductors (CMOSs), complemen- tary inverters, D flip-flops, rectifiers, and ring oscillators, that make use of the compounds and the semiconductor materials disclosed herein also as well as methods of making the same are within the scope of the present invention.

Accordingly, the present invention provides articles of manufacture such as the various devices described herein that include a composite having a semiconductor material of the present invention comprising compound of formula (I), a substrate component, and/or a dielectric component. The substrate component can be selected from materials including doped silicon, an indium tin oxide (ITO), ITO-coated glass, ITO-coated polyimide or other plastics, aluminum or other metals alone or coated on a polymer or other substrate, a doped polythiophene or other poly- mers, and the like. The dielectric component can be prepared from inorganic dielectric materials such as various oxides (e.g., S1O2, AI2O3, Hf02), organic dielectric materials such as various polymeric materials (e.g., polycarbonate, polyester, polystyrene, polyhaloethylene, polyacry- late), self-assembled superlattice/self-assembled nanodielectric (SAS/SAND) materials (e.g., described in Yoon, M-H. et al., PNAS, 102 (13): 4678-4682 (2005), the entire disclosure of which is incorporated by reference herein), and hybrid organic/inorganic dielectric materials (e.g., described in U.S. Patent Application Serial No. 1 1/642,504, the entire disclosure of which is incorporated by reference herein). In some embodiments, the dielectric component can include the crosslinked polymer blends described in U.S. Patent Application Serial Nos.

1 1/315,076, 60/816,952, and 60/861 ,308, the entire disclosure of each of which is incorporated by reference herein. The composite also can include one or more electrical contacts. Suitable materials for the source, drain, and gate electrodes include metals (e.g., Au, Al, Ni, Cu), transparent conducting oxides (e.g., ITO, IZO, ZITO, GZO, GIO, GITO), and conducting polymers (e.g., poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), polyaniline (PANI), polypyrrole (PPy)). One or more of the composites described herein can be incorporated within various organic electronic, optical, and optoelectronic devices such as organic thin film transistors (OTFTs), specifically, organic field effect transistors (OFETs), as well as sensors, capacitors, unipolar circuits, complementary circuits (e.g., inverter circuits), and the like.

An aspect of the present invention, therefore, relates to methods of fabricating an organic field effect transistor that incorporates a semiconductor material of the present invention comprising compounds of formula (I). The semiconductor materials of the present invention can be used to fabricate various types of organic field effect transistors including top-gate top-contact capacitor structures, top-gate bottom-contact capacitor structures, bottom-gate top-contact capacitor structures, and bottom-gate bottom-contact capacitor structures.

In certain embodiments, OTFT devices can be fabricated with the present compounds of formula (I) on doped silicon substrates, using S1O2 as the dielectric, in top-contact geometries. In particular embodiments, the active semiconducting layer which incorporates at least a compound of the present invention can be deposited by vacuum vapor deposition at room temperature or at an elevated temperature. In other embodiments, the active semiconducting layer which incorporates at least a compound of the present invention can be applied by solution-based process, for example, spin-coating or jet printing. For top-contact devices, metallic contacts can be patterned on top of the films using shadow masks.

In certain embodiments, OTFT devices can be fabricated with the present compounds of formula (I) on plastic foils, using polymers as the dielectric, in top-gate bottom-contact geometries. In particular embodiments, the active semiconducting layer which incorporates at least a compound of the present invention can be deposited at room temperature or at an elevated temperature. In other embodiments, the active semiconducting layer which incorporates at least a compound of the present invention can be applied by spin-coating or printing as described herein. Gate and source/drain contacts can be made of Au, other metals, or conducting polymers and deposited by vapor-deposition and/or printing. Other articles of manufacture in which compounds of formula (I) of the present invention are useful as photovoltaics or solar cells. Compounds of the present invention can exhibit broad optical absorption and/or a very positively shifted reduction potential making them desirable for such applications. Accordingly, the compounds of formula (I) described herein can be used as a p-type semiconductor in a photovoltaic design, which includes an adjacent n-type semiconduct- ing material that forms a p-n junction. The compounds can be in the form of a thin film semiconductor, which can be a composite of the thin film semiconductor deposited on a substrate. Exploitation of compounds of the present invention in such devices is within the knowledge of the skilled artisan.

Accordingly, another aspect of the present invention relates to methods of fabricating an organic light-emitting transistor, an organic light-emitting diode (OLED), or an organic photovoltaic device that incorporates one or more semiconductor materials of the present invention. The following examples are provided to illustrate further and to facilitate understanding of the present invention and are not in any way intended to limit the invention.

Examples Example 1 Synthesis of 2, 3-dibromo-1 ,4-bis-trimethylsilanyl-benzene

LDA (2 M, 70 mL, 140 mmol) was added dropwise to a solution of 1 ,2-dibromobenzene (15.0 g, 64 mmol) and chlorotrimethylsilane (20 mL, 153 mmol) in THF (90 mL) at -78 °C. The resultant brown suspension was stirred at -78 °C for 30 min and then gradually warmed to room temperature. The reaction mixture was stirred for 18 h and then cooled to -78 °C again and chlorotrimethylsilane (20 mL, 153 mmol) was added. LDA (2M, 70 mL, 140 mmol) was added dropwise and the resultant brown suspension was stirred at -78 °C for 30 mins and then gradually warmed to room temperature. The reaction mixture was stirred for a further 18 h and then hy- drolyzed with 1 N HCI (100 mL). The resultant mixture was extracted with diethyl ether (3 x 200 mL) and the combined organic layers concentrated to give a brown oil, which was used directly in the next step without further purification. ¹H NMR (400 MHz, CDCI₃) δ 7.34 (s, 2H), 0.40

(18H).

Example 2 Synthesis of 2,3-dibromo-1 ,4-diiodo-benzene

Iodine monochloride (1 M, 60 mL, 58 mmol) was added to a solution of 2,3-dibromo-1 ,4-bis- trimethylsilanyl-benzene (10.0 g, 26.3 mmol) in dichloromethane (105 mL) at 0 °C. The resultant purple solution was stirred at room temperature for 1 day. The reaction was cooled to 0 °C and additional iodine monochloride (1 M, 60 mL, 58 mmol) was added. The reaction mixture was stirred at room temperature for a further 1 day. Saturated sodium thiosulfate solution (150 mL) was added to the reaction mixture and extracted with dichloromethane (2 x 100 mL). The combined organic layers were concentrated to give a brown solid, which was purified by column chromatography on silica gel using 100% hexanes to yield a brown solid (8 g, 69%). ¹H NMR (400 MHz, CDCIs) δ 7.47 (s, 2H).

Example 3 Synthesis of 2-[2,3-dibromo-4-(4,4,5,5-tetramethyl-1 ,3,2-dioxaborolan-2- yl)phenyl]-4,4,5,5-tetramethyl-1 ,3,2-dioxaborolane

iPrMgCI (2M, 77 mL, 153 mmol) was added drop wise to a solution of 2,3-dibromo-1 ,4-diiodo- benzene at -78 °C over 45 min and the resultant mixture stirred at -78 °C for 3 h. 2-lsopropoxy- 4,4, 5, 5-tetramethyl-1 ,3,2-dioxaborolane (38 g, 42 mL, 205 mmol) was added drop wise to the stirring mixture at -78 °C over 30 minutes the resultant reaction mixture was stirred at room temperature for 16 h. The reaction mixture was quenched with saturated ammonium chloride solution (120 mL) and extracted with diethyl ether (2 x 100 mL). The combined organic extracts were dried over MgSC and concentrated in vacuo to give crude solids. The residue was triturated with ethanol at room temperature and the solids collected by gravity filtration and dried under high vacuum to give white solid (19.2 g, 76%). ¹H NMR (400 MHz, CDCIs) δ 7.39 (s, 2H), 1 .37 (s, 24H).

Example 4 Synthesis of 2-tetradecylthiophene

n-BuLi (1.6 M, 48 mL, 76 mmol) was added dropwise to a solution of thiophene (7.0 g, 83 mmol) in THF (70 mL) at -78 °C and stirred for 45 min. Tetradecyl bromide (23 mL, 76 mmol) in THF (25 mL) was added dropwise to the resultant suspension and then gradually warmed to room temperature and stirred for 18 h. The reaction mixture was quenched with water (60 mL) and extracted with diethyl ether (2 x 100 mL). The combined organic extracts were dried over MgSC and concentrated to give a brown oil (20.7 g, 97%), which was used directly in the next step without further purification. 1 H NMR (400 MHz, CDCIs) δ 7.10 (d, 1 H, J = 5.2 Hz), 6.91 (t, 1 H, J = 4.4 Hz), 6.77 (d, 1 H, J = 3.2 Hz), 2.82 (t, 2H, J = 7.6 Hz), 1.68 (q, 2H, J = 6.8 Hz), 1.50- 1 .20 (m, 22H), 0.88 (t, 3H, J = 6.8 Hz).

Example 5 Synthesis of 2-bromo-5-tetradecylthiophene Q-^C"^¾ DCM^N0 ^SC _{to rt} ' ^Br^Q-^C«¾

To a solution of 2-tetradecylthiophene (20.7 g, 74 mmol) in anhydrous DCM (64 mL) at 0 °C was added NBS (13.67 g, 76 mmol) portion-wise. The yellow solution was allowed to stir at room temperature in the dark. The reaction was monitored by NMR. After 3 hours, the reaction mixture was quenched with water and the organic layer was extracted with DCM (x3). The organic extract was washed with water (x2), brine (x1 ) and dried over MgSC . The crude material was purified using flash column chromatography (100% hexane) to obtain the title compound as a pale yellow oil (21.75 g, 82%). 1 H NMR (400 MHz, CDCI₃) δ 6.82 (d, 1 H, J = 3.6 Hz), 6.51 (d, 1 H, J = 3.6 Hz), 2.72 (t, 2H, J = 8.0 Hz), 1.60 (m, 2H), 1 .32-1 .24 (m, 22H), 0.87 (t, 3H, J = 6.8 Hz).

Example 6 Synthesis of 3-bromo-5-tetradecylthiophene

A commercial LDA solution (2 M, 24 ml, 47 mmol) was diluted in THF (65 ml) solution at 0 °C. A solution of 2-bromo-5-tetradecylthiophene (14 g, 39 mmol) in THF (65 ml) was added drop wise to the dilute LDA solution at 0 °C over 60 mins using a dropping funnel. The resultant mixture was gradually warmed to room temperature and stirred for 3 hrs. The reaction mixture was quenched with water (150 ml) and extracted with Et.20 (2 x 100 ml). The combined organic layers were washed with brine and concentrated to give a brown oil, which was used purified by column chromatography on silica gel using 100% hexanes to yield yellow oil (12.5 g, 89%). 1 H NMR (400 MHz, CDCI₃) δ 6.99 (s, 1 H), 6.70 (s, 1 H), 2.77 (t, 2H, J = 8 Hz), 1 .65 (q, 2H, J = 8 Hz), 1 .44-1 .20 (m, 22H), 0.89 (t, 3H, J = 6.8 Hz).

Example 7 Synthesis of Trimethyl-tributylstannanylethynyl-silane

H

n-BuLi (1.6 M, 24.4 mL, 39 mmol) was added dropwise to a solution of ethynyltrimethylsilane (4.0 g, 41 mmol) in THF (40 mL) at -78 °C and gradually warmed to 0 °C over 30 min. The reaction mixture was cooled to -78 °C again and tributyltin chloride (1 1.4 mL, 39 mmol) in THF (30 mL) was added dropwise to the resultant mixture. The reaction mixture was stirred for 18 h at room temperature and quenched with water (20 mL). The mixture was extracted with diethyl ether (2 x 100 mL) and the combined organic extracts were washed with brine (50 mL). The organic phase was dried and concentrated to give a yellow oil (15.0 g, 95%), which was used directly in the next step without further purification. 1 H NMR (400 MHz, CDCI₃) δ 1 .67-1.45 (m, 6H), 1 .45-1.20 (m, 6H), 0.98 (t, 6H, J = 8.4 Hz), 0.90 (t, 9H, J = 7.2 Hz), 0.16 (s, 9H).

Example 8 Synthesis of 2,3-dibromo-1 ,4-bis(5-tetradecyl-thiophen-2-yl) benzene

Tetrakis(triphenylphosphine)palladium(0) (1.8 g, 1.47 mmol) was added to a solution of 2-[2,3- dibromo-4-(4,4,5,5-tetramethyl-1 ,3,2-dioxaborolan-2-yl)phenyl]-4,4,5,5-tetramethyl-1 ,3,2- dioxaborolane (7.2 g, 14.76 mmol), 3-bromo-5-tetradecylthiophene (16.53 g, 46 mmol) and aqueous sodium carbonate solution (2M, 32 mL, 65 mmol) in DME (64 mL) and stirred at 100 °C for 6 h. The reaction mixture was cooled to room temperature and diluted with water (100 mL). The mixture was extracted with dichloromethane (2 x 30 mL). The combined organic phases were dried and concentrated to give a brown oil, which was purified by column chroma- tography to yield white solids (7.5 g, 64%). 1 H NMR (400 MHz, CDCI₃) δ 7.29 (s, 2H), 7.12 (s, 2H), 6.92 (s, 2H), 2.83 (t, 4H, J = 7.6 Hz), 1 .75-1 .67 (m, 4H), 1 .50-1 .20 (m, 44H), 0.88 (t, 6H, J = 6.4 Hz).

Example 9 Synthesis of 2,3-bis(ethynyltrimethylsilane)-1 ,4-bis(5-tetradecyl-thiophen-2- yl)benzene

Tetrakis(triphenylphosphine)palladium(0) (1 .3 g, 0.95 mmol) was added to a solution of trime- thyl-tributylstannanylethynyl-silane (1 1 .1 g, 28.5 mmol) and 2,3-dibromo-1 ,4-bis(5-tetradecyl- thiophen-2-yl) benzene (7.5 g, 9.5 mmol) in toluene (100 mL) and stirred at 100 °C for 3 h. The reaction mixture was cooled to room temperature and diluted with aqueous saturated ammonium chloride solution (100 mL). The toluene layer was separated and dichloromethane was added. The mixture was extracted with dichloromethane (3 x 30 mL). The combined organic phases were dried and concentrated to give a brown oil, which was purified by column chromatography to yield white solids (7.68 g, 99%). 1 H NMR (400 MHz, CDCI₃) δ 7.43 (s, 2H), 7.36 (s, 2H), 7.25 (s, 2H), 2.82 (t, 4H, J = 7.6 Hz), 1 .45-1 .20 (m, 44H), 0.88 (t, 6H, J = 6.8 Hz), 0.22 (s, 18H).

Example 10 Synthesis of 2,3-diethynyl-1 ,4-bis(5-tetradecyl-thiophen-2-yl)benzene

Tetrabutylammonium fluoride (1 M, 23 ml_, 22.8 mmol) was added to a solution of 2,3- bis(ethynyltrimethylsilane)-1 ,4-bis(5-tetradecyl-thiophen-2-yl)benzene (7.86 g, 9.5 mmol) at room temperature and the reaction was stirred for 1 h. The reaction mixture was diluted with aqueous saturated ammonium chloride solution (100 ml_). The mixture was extracted with diethyl ether (3 x 50 ml_). The combined organic phases were dried and concentrated to give brown solids, which were purified by column chromatography to yield brown solids (3.6 g, 55%). 1 H NMR (400 MHz, CDCI₃) δ 7.44 (s, 2H), 7.40 (s, 2H), 7.12 (s, 2H), 3.42 (s), 2.82 (t, 4H, J = 8.0 Hz), 1 .60-1 .80 (m, 4H), 1 .45-1 .20 (m, 44H), 0.88 (t, 6H, J = 6.8 Hz).

Example 11 Synthesis of 2,7-ditetradecyl- phenanthro[2,1 -b : 7,8-b']dithiophene 1

W(CO)₅(THF) (3.0 g, 8.5 mmol) was formed by irradiating W(CO)₆ in THF (75ml_) under UVA lamp at 60 °C for 2 h where the colorless reaction mixture turns to yellow-green after 2 h. The solution of W(CO)5(THF) in THF was transferred quickly into a flask of stirring 2,3-diethynyl-1 ,4- bis(5-tetradecyl-thiophen-2-yl)benzene in THF (50ml_) at room temperature and the reaction mixture stirred for 48 h in the dark. The reaction mixture was filtered through a thin silica gel pad and a celite pad, and then washed with copious amounts of chloroform. The filtrate was concentrated and the resultant residue triturated with hexanes. The solids were collected by suction filtration and recrystallized from hot hexanes to give the title compound 1 as a white solid (880 mg, 29%). 1 H NMR (400 MHz, CDC ) δ 8.60 (d, 2H, J= 8 Hz), 8.36 (s, 2H), 7.99 (d, 2H, J = 8

Hz), 7.73 (s, 2H), 3.05 (t, 4H, J = 8 Hz), 1 .80-1.90 (m, 4H), 1.5-1 .2 (m, 44H), 0.89 (t, 6H, J Hz).

Examples 12-16 Compounds 2, 3, 4, 5 and 6 were synthesized in the same way as described above.

2,7-dihexyl- phenanthro[2,1 -b : 7,8-b']dithiophene 2

White solid (695 mg, 1 1 %). 1 H NMR (400 MHz, CDCI₃) δ 8.60 (d, 2H, J = 9.2 Hz), 8.37 (s, 2H), 7.99 (d, 2H, J = 8.8 Hz), 7.73 (s, 2H), 3.04 (t, 4H, J = 7.2 Hz), 1 .90-1.75 (m, 4H), 1.5-1.25 (m, 6H), 0.89 (t, 6H, J = 7.2 Hz). 2,7-dioctyl- phenanthro[2,1 -b : 7,8-b']dithiophene 3

White solid (160 mg, 13%). 1 H NMR (400 MHz, CDCI₃) δ 8.62 (d, 2H, J = 9.2 Hz), 8.37 (s, 2H), 8.01 (d, 2H, J = 8.8 Hz), 7.74 (s, 2H), 3.05 (t, 4H, J = 7.2 Hz), 1 .83 (m, 4H), 1 .48-1 .30 (m, 10H), 0.86 (t, 6H, J = 7.2 Hz).

2,7-didecyl- phenanthro[2,1 -b : 7,8-b']dithiophene 4

White solid (1.0 g, 19%). 1 H NMR (400 MHz, CDCI₃) δ 8.61 (d, 2H, J = 9.2 Hz), 8.37 (s, 2H), 8.01 (d, 2H, J = 8.8 Hz), 7.74 (s, 2H), 3.04 (t, 4H, J = 7.2 Hz), 1.83 (m, 4H), 1 .46-1.28 (m, 14H), 0.89 (t, 6H, J = 7.2 Hz).

2,7-didodecyl- phenanthro[2,1 -b : 7,8-b']dithiophene 5

White solid (360 mg, 10%). 1 H NMR (400 MHz, CDCI₃) δ 8.60 (d, 2H, J = 9.2 Hz), 8.37 (s, 2H), 8.01 (d, 2H, J = 8.8 Hz), 7.74 (s, 2H), 3.04 (t, 4H, J = 7.2 Hz), 1.81 (m, 4H), 1 .48-1.25 (m, 18H), 0.88 (t, 6H, J = 7.2 Hz).

2,7-dihexadecyl- phenanthro[2,1 -b : 7,8-b']dithiophene 6

White solid (160 mg, 7%). 1 H NMR (400 MHz, CDCI₃) δ 8.61 (d, 2H, J = 9.2 Hz), 8.37 (s, 2H), 8.01 (d, 2H, J = 8.8 Hz), 7.74 (s, 2H), 3.04 (t, 4H, J = 7.2 Hz), 1.82 (m, 4H), 1 .46-1.26 (m, 26H), 0.88 (t, 6H, J = 7.2 Hz).

Example 17 Synthesis of 2-(2-thienyl)hexan-2-ol

n-BuLi (1.6 M, 96 mL, 154 mmol) was added drop wise to a solution of 2-bromothiophene (25.0 g, 154 mmol) in THF (150 mL) at -78 °C over 45 min and stirred for 30 min. 2-Hexanone (17 mL, 139 mmol) in THF (50 mL) was added drop wise to the resultant suspension over 45 min and then kept in the dry ice-acetone cooling bath and stirred for 18 h. The reaction mixture was warmed to room temperature and quenched with saturated aqueous ammonium chloride solution (200 mL) and extracted with diethyl ether (3 x 100 mL). The combined organic extracts were dried over MgS0₄ and concentrated to give a pale red oil as crude product, which was purified by column chromatography on silica gel using 100% hexanes and hexanes/ethyl acetate (v/v 5:1 ) to yield pale red oil (18.1 g, 64%). 1 H NMR (400 MHz, CDCI₃) δ 7.19 (d, 1 H, J =

5.2 Hz), 6.91 (dd, 1 H, J = 16 Hz), 6.63 (d, 1 H, J = 3.6 Hz), 1 .87-1.20 (m, 1 1 H), 0.98 (t, 3H, J 1 .2 Hz).

Example 18 Synthesis of 2-(1 -methylpentyl)thiophene

Boron trifluoride diethyl etherate was added drop wise to a mixture of 2-(2-thienyl)hexan-2-ol and triethylsilane in methylene chloride (180 mL) over 30 mins at -78 °C. The reaction mixture was kept in dry ice-acetone cooling bath and stirred for 18 h. The reaction was quenched with saturated aqueous sodium bicarbonate solution (90 mL) and then diluted with methylene chloride (50 mL). The resultant mixture was extracted with methylene chloride (3 x 100 mL). The combined organic phases were dried over MgS0₄, filtered and concentrated to give a crude product. The crude product was purified by column chromatography on silica gel using 100% hexanes to yield colorless oil (13.6 g, 82%). 1 H NMR (400 MHz, CDCI₃) δ 7.1 1 (d, 1 H, J = 5.2 Hz), 6.91 (dd, 1 H, J = 0.4 Hz, 4.8 Hz), 6.78 (d, 1 H, J = 4.0 Hz), 3.01 (m, 1 H), 1.67-1.45 (m, 2H), 1 .35-1.20 (m, 7H), 0.87 (t, 3H, J = 7.2 Hz).

Example 19 Synthesis of 2-bromo-5-(1 -methylpentyl)thiophene

N-Bromosuccinimide (16 g, 82 mmol) was added portion wise (4 x 4 g portions) to a stirring solution of 2-(1 -methylpentyl)thiophene (13.6 g, 81 mmol) at 0 °C over 40 min at 10-minute inter- vals and stirred for 90 min at room temperature. The reaction was completed by 1 H NMR analysis and water (100 mL) was added. The resultant mixture was extracted with methylene chloride (3 x 75 mL). The combined organic phases were dried over MgSC , filtered and concentrated to give the crude product. The crude product was purified by column chromatography on silica gel using 100% hexanes to yield red oil (14.0 g, 70%). 1 H NMR (400 MHz, CDCI₃) δ 6.84 (d, 1 H, J = 7.2 Hz), 6.53 (d, 1 H, J = 7.2 Hz), 2.92 (m, 1 H), 1 .67-1 .45 (m, 2H), 1 .35-1 .20 (m, 7H), 0.87 (t, 3H, J = 7.2 Hz).

Example 20 Synthesis of 4-bromo-2-(1 -methylpentyl)thiophene

Commercially available LDA solution (2 M, 57 ml, 1 14 mmol) was diluted in THF (90 ml) solution at 0 °C. A solution of 2-bromo-5-(1 -methylpentyl)thiophene (14 g, 57 mmol) in THF (50 ml) was added drop wise to the dilute LDA solution at 0 °C over 60 mins using a dropping funnel. The resultant mixture was gradually warmed to room temperature and stirred for 3 hrs. The reaction mixture was quenched with water (100 ml) and extracted with Et.20 (3 x 75 ml). The combined organic layers were washed with brine and concentrated to give a brown oil, which was used purified by column chromatography on silica gel using 100% hexanes to yield pale yellow oil (12.5 g, 89%). 1 H NMR (400 MHz, CDC ) δ 7.01 (s, 1 H), 6.70 (s, 1 H), 2.92 (m, 1 H), 1 .67-1 .45 (m, 2H), 1 .35-1 .20 (m, 7H), 0.87 (t, 3H, J = 7.2 Hz). Example 21 Synthesis of 2,3-dibromo-1 ,4-bis[5-(1 -methylpentyl)thiophen-2-yl]benzene

Tetrakis(triphenylphosphine)palladium(0) (2.8 g, 2.5 mmol) was added to a solution of 2-[2,3- dibromo-4-(4,4,5,5-tetramethyl-1 ,3,2-dioxaborolan-2-yl)phenyl]-4,4,5,5-tetramethyl-1 ,3,2- dioxaborolane (12 g, 25.0 mmol), 4-bromo-2-(1 -methylpentyl)thiophene (14.8 g, 60 mmol) and aqueous sodium carbonate solution (2M, 50 mL, 1 10 mmol) in DME (100 mL) and stirred at 100 °C for 6 h. The reaction mixture was cooled to room temperature and diluted with water (100 mL). The mixture was extracted with dichloromethane (3 x 50 mL). The combined organic phases were dried and concentrated to give a brown oil, which was purified by column chromatography to yield a pale yellow oil (9.7 g, 68%). 1 H NMR (400 MHz, CDCI₃) δ 7.30 (s, 2H), 7.13 (s, 2H), 6.93 (s, 2H), 3.01 (m, 2H), 1 .67-1.45 (m, 4H), 1 .35-1 .20 (m, 14H), 0.87 (t, 6H, J = 7.2 Hz).

Example 22 Synthesis of 2,3-bis(ethynyltrimethylsilane)-1 ,4-bis[5-(1 -methylpentyl)thiophen- 2-yl]benzene

Tetrakis(triphenylphosphine)palladium(0) (1 .9 g, 1.7 mmol) was added to a solution of 2,3- dibromo-1 ,4-bis[5-(1 -methylpentyl)thiophen-2-yl]benzene (9.7 g, 17 mmol)and trimethyl- tributylstannanylethynyl-silane (15.8 g, 40.8 mmol) in toluene (90 mL) and stirred at 100 °C for 3 h. The reaction mixture was cooled to room temperature and diluted with aqueous saturated ammonium chloride solution (90 mL). The toluene layer was separated and dichloromethane was added. The mixture was extracted with dichloromethane (3 x 50 mL). The combined organic phases were dried and concentrated to give a brown oil, which was purified by column chromatography to yield a red oil (10 g, 99%). 1 H NMR (400 MHz, CDCI₃) δ 7.46 (s, 2H), 7.37 (s, 2H), 7.14 (s, 2H), 3.01 (m, 2H), 1 .67-1 .45 (m, 4H), 1 .35-1 .20 (m, 14H), 0.87 (t, 6H, J = 7.2 Hz), 0.22 (s, 18H). Example 23 Synthesis of 2,3-diethynyl-1 ,4-bis[5-(1 -methylpentyl)thiophen-2-yl]benzene

Tetrabutylammonium fluoride solution in THF (1 M, 45 ml_, 47.6 mmol) was added to a solution of 2,3-bis(ethynyltrimethylsilane)-1 ,4-bis[5-(1 -methylpentyl)thiophen-2-yl]benzene (10.25 g, 9.5 mmol) in THF (50 ml.) at room temperature and the reaction was stirred for 3 h. The reaction mixture was diluted with aqueous saturated ammonium chloride solution (50 ml_). The mixture was extracted with diethyl ether (3 x 50 ml_). The combined organic phases were dried and concentrated to give brown solids, which were purified by column chromatography using 100% hexanes and then hexanes/dichloromethane (v/v 4:1 ) to yield a green oil (5.9 g, 75%). 1 H NMR (400 MHz, CDCIs) δ 7.45 (s, 2H), 7.43 (s, 2H), 7.15 (s, 2H), 3.02 (m, 2H), 1 .67-1 .45 (m, 4H), 1 .35-1 .20 (m, 14H), 0.87 (t, 6H, J = 7.2 Hz). Example 24 Synthesis of 2,7-di(1 -methylpentyl)- phenanthro[2,1 -b : 7,8-b']dithiophene 7

W(CO)₅(THF) was formed by irradiating W(CO)₆ (1 .8 g, 2.6 mmol) in THF (75ml_) under UVA lamp at 60 °C for 2 h where the colorless reaction mixture turns to yellow-green after 2 h. The solution of W(CO)5(THF) in THF was transferred quickly into a flask of stirring 2,3-diethynyl-1 ,4- bis[5-(1 -methylpentyl)thiophen-2-yl]benzene (3.0 g, 12.9 mmol) in THF (50ml_) at room temperature and the reaction mixture stirred for 48 h in the dark. The reaction mixture was concentrated in vacuo and the resultant residue redissolved in warm hexanes (30 °C) and wet loaded onto silica gel column. Column chromatography using 100% hexanes gave a crude product. The crude product was recrystallized from ethanol and then subjected to sublimation to give pale yellow solids (380 mg, 12%). 1 H NMR (400 MHz, CDCIs) δ 8.61 (d, 2H, J = 9.2 Hz), 8.39 (s, 2H), 8.01 (d, 2H, J = 8.8 Hz), 3.22 (m, 2H), 1 .90-1.70 (m, 4H), 1 .46 (d, 6H, J = 7.2 Hz), 1 .40- 1 .30 (m, 8H), 0.90 (t, 6H, J = 6.8 Hz). Example 25

General procedure for device fabrication of bottom-gate top-contact OFETs 30 nm ALD AI2O3 coated, highly doped silicon wafers were thoroughly cleaned with organic solvents and after a short oxygen plasma treatment functionalized with an alkyl phosphonic monolayer (ie. decyl- or octadecylphosphonic acid) from solution. The highly doped silicon is used as substrate and back gate electrode, the alkyl phosphonic acid treated AI2O3 acts as the gate dielectric. The organic semiconductor was thermally evaporated in high vacuum (<10^-5 mbar) while the substrate was held at a defined temperature. A 50 nm-thick of Au layer for source and drain electrodes was deposited though a shadow mask to give top contact OFET devices. The channel width (W) was 500 μηη and channel length (L) was 100 μηη typically. All electrical measurements are performed in ambient air in the dark using a B1500 Agilent parameter analyzer. All the OFETs based on phenacene derivative showed typical p-type characteristics. To record the transfer curve the drain-source voltage (VDS) was held to -5 V. The charge-carrier mobility (μ) was extracted in the saturation regime from the slope of (ld)^{1 2} versus VGS using the equation μ = 2L/(W*Ci)*(d lD^{1 2}/dVGs)² . The threshold voltage (V_th) was extracted from the intersection of the linear extrapolation of the ld^{1 2} versus VGS plot with the VGS axis. The performance of the OFETs are summarized in Table 1 and Figures 1 and 2.

Figures 1A, 2A and 3A show the respective output characteristics of vacuum deposited OFETs for compounds 1 , 2, and 7. In these figures, the drain current is plotted against the drain-source voltage. Figures 1 B, 2B and 3B show the transfer characteristics for these compounds, respectively. In these figures, the drain current is plotted against the gate-source voltage.

Claims

1 . Phenacene compounds of formula I

wherein

2. Phenacene compounds according to claim 1 , wherein R¹ and R² are independently of each other linear or branched a Ce-14 alkyl group.

3. Phenacene compounds according to claim 1 or 2, wherein R¹ and R² are selected from the group consisting of n-hexadecyl, n-tetradecyl, n-dodecyl, n-decyl, n-octyl, n-hexyl and

1 -methylpentyl.

4. A thin film semiconductor comprising one or more compounds of any one of claims 1 - 3.

5. A field effect transistor device comprising the thin film semiconductor of claim 4.

6. A photovoltaic device comprising the thin film semiconductor of claim 4.

7. An organic light emitting diode device comprising the thin film semiconductor of claim 4.

8. A unipolar or complementary circuit device comprising the thin film semiconductor of claim 4.