Mono-, oligo- and polymers of benzo[b]thiophene...

Details Mono-, oligo- and polymers of benzo[b]thiophene... Mono-, oligo- and polymers of benzo[b]thiophene...

2002-09-27

2004-02-24

Huff, Mark F. (Department: 1756)

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

C252S299610, C549S032000, C549S061000, C549S070000

Reexamination Certificate

active

06695978

ABSTRACT:

FIELD OF INVENTION
The invention relates to new conjugated mono-, oligo- and polymers of benzo[b]thiophene (thianaphthene) and bisbenzo[b]thiophene (bithianaphthene). The invention further relates to their use as semiconductors or charge transport materials in optical, electrooptical or electronic devices including field effect transistors, electroluminescent, photovoltaic and sensor devices. The invention further relates to field effect transistors and semiconducting components comprising the new mono-, oligo- and polymers.
BACKGROUND AND PRIOR ART
Organic materials have recently shown promise as the active layer in organic based thin film transistors and organic field effect transistors [see H. E. Katz, Z. Bao and S. L. Gilat, Acc. Chem. Res., 2001, 34, 5, 359]. Such devices have potential applications in smart cards, security tags and the switching element in flat panel displays. Organic materials are envisaged to have substantial cost advantages over their silicon analogues if they can be deposited from solution, as this enables a fast, large-area fabrication route.
The performance of the device is principally based upon the charge carrier mobility of the semiconducting material and the current on/off ratio, so the ideal semiconductor should have a low conductivity in the off state, combined with a high charge carrier mobility (>1×10
−3
cm
2
V
−1
s
−1
). In addition, it is important that the semiconducting material is relatively stable to oxidation, i.e., it has a high ionisation potential, as oxidation leads to reduced device performance.
A known compound which has been shown to be an effective p-type semiconductor for OFETs is pentacene [see S. F. Nelson, Y. Y. Lin, D. J. Gundlach and T. N. Jackson,
Appl. Phys. Lett.,
1998, 72, 1854]. When deposited as a thin film by vacuum deposition, it was shown to have carrier mobilities in excess of 1 cm
2
V
−1
s
−1
with very high current on/off ratios greater than 10
6
. However, vacuum deposition is an expensive processing technique that is unsuitable for the fabrication of large-area films.
Regular poly(3-hexylthiophene) has been reported with charge carrier mobility between 1×10
−5
and 4.5×10
−2
cm
2
V
−1
s
−1
, but with a rather low current on/off ratio between 10 and 10
3
[see Z. Bao et al.,
Appl. Pys. Lett.
1997, 78, 2184]. In general, poly(3-alkylthiophenes) show improved solubility and are able to be solution processed to fabricate large area films. However, poly(3-alkylthiophenes) have relatively low ionisation potentials and are susceptible to doping in air [see H. Sirringhaus et al.,
Adv. Solid State Phys.
1999, 39, 101].
It is an aim of the present invention to provide new materials for use as semiconductors or charge transport materials, which are easy to synthesize, have high charge mobility, good processibility and improved oxidative stability. Other aims of the invention are immediately evident to those skilled in the art from the following description.
The inventors have found that these aims can be achieved by providing new monomers, oligomers and polymers based on benzo[b]thiophene and 2,2′-bisbenzo[b]thiophene. Thus, benzo[b]thiophene (1) and 2,2′-bisbenzo[b]thiophene (2) are heterocycles that exhibit good conjugation and planarity. The introduction of alkyl chains R further improves solubility and solution processibility. Poly(2,5-benzo[b]thiophene) (3) and poly(2,2′-bisbenzo[b]thiophene) (4) exhibit a high degree of planarity in the backbone and strong interchain pi—pi-stacking interactions making them effective charge transport materials with high carrier mobilities. Also, the incorporation of alkyl substitutents R leads to good solubility and thus good solution processibility of the materials according to the present invention. Solution processing during device manufacture has the advantage over vaccum deposition of being a potentially cheaper and faster technique.
The synthesis of 2,2′-bisbenzo[b]thiophene (2) has been reported by Y. Fort et al.,
Tetrahedron,
1994, 50, 41, 11893. Unsubstituted poly(benzo[b]thiophene) has been reported via an electrochemical polymerisation (J. Electroanal. Chem. 2001, 510(1-2), 29-34, Makromol. Chem. Rapid Commun., 1987, 8, 325-9). The synthesis of substituted poly(2,5-benzo[b]thiophene) has not been reported. Moreover, mono- and poly(2,2′-bisbenzo[b]thiophenes) according to the present invention have not been reported.
A further aspect of the invention relates to reactive mesogens consisting of a central core comprising one or more benzo[b]thiophene or 2,2′-bisbenzo[b]thiophene units, and optionally comprising further unsaturated organic groups that form a conjugated system together with the (bis)benzo[b]thiophene units, said core being linked, optionally via a spacer group, to one or two polymerisable groups. The reactive mesogens can induce or enhance liquid crystal phases or are liquid crystalline themselves. They can be oriented in their mesophase and the polymerisable group can be polymerised or crosslinked in situ to form polymer films with a high degree of order, thus yielding improved semiconductor materials with high stability and high charge carrier mobility.
Grell et al., J.
Korean Phys. Soc.
2000, 36(6), 331 suggest a reactive mesogen comprising a conjugated distyrylbenzene core with two reactive acrylate end groups as a model compound for molecular electronics. However, there is no disclosure of reactive mesogens of 2,2′-bisbenzo[b]thiophene.
A further aspect of the invention relates to liquid crystal polymers, in particular liquid crystal side chain polymers obtained from the reactive mesogens according to the present invention, which are then further processed, e.g., from solution as thin layers for use in semiconductor devices.
Definition of Terms
The terms ‘liquid crystalline or mesogenic material’ or ‘liquid crystalline or mesogenic compound’ means materials or compounds comprising one or more rod-shaped, lath-shaped or disk-shaped mesogenic groups, i.e., groups with the ability to induce liquid crystal phase behaviour. The compounds or materials comprising mesogenic groups do not necessarily have to exhibit a liquid crystal phase themselves. It is also possible that they show liquid crystal phase behaviour only in mixtures with other compounds, or when the mesogenic compounds or materials, or the mixtures thereof, are polymerised.
The term ‘polymerisable’ includes compounds or groups that are capable of participating in a polymerisation reaction, like radicalic or ionic chain polymerisation, polyaddition or polycondensation, and reactive compounds or reactive groups that are capable of being grafted, for example, by condensation or addition to a polymer backbone in a polymeranaloguous reaction.
The term ‘film’ includes self-supporting, i.e., free-standing, films that show more or less pronounced mechanical stability and flexibility, as well as coatings or layers on a supporting substrate or between two substrates.
SUMMARY OF THE INVENTION
One object of the invention are mono-, oligo- and polymers of formula I
R
1
—[(A)
a
—(B)
b
—(C)
c
]
n
—R
2
wherein
A and C are independently of each other —CX
1
═CX
2
—, —C═C—, or optionally substituted arylene or heteroarylene,
X
1
and X
2
are independently of each other H, F, Cl or CN,
B is 2,5-benzo[b]thiophene or 2,2′-bisbenzo[b]thiophene that is optionally substituted with one or more groups R,
R is H, halogen, straight chain, branched or cyclic alkyl with 1 to 20 C-atoms, which may be unsubstituted, mono- or polysubstituted by F, Cl, Br, I or CN, it being also possible for one or more non-adjacent CH
2
groups to be replaced, in each case independently from one another, by —O—, —S—, —NH—, —NR
0
—, —SiR
0
R
00
—, —SnR
0
R
00
—, —CO—,

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