WO2009009790A1 - Air-stable, high hole mobility thieno-thiophene derivatives - Google Patents

Abstract

Compounds with high calculated hole mobilities that are also air-stable are dislcosed. The compounds can be used in and to improve the efficiency of a variety of devices, such as organic field effect transistors, radio frequency identification devices, and organic photovoltaic devices.

Description

Air-Stable, High Hole Mobility Thieno-Thiophene

Derivatives

Related Applications

This application claims the benefit of priority to United States Provisional Patent

Application serial number 60/949,342, filed July 12, 2007; the contents of which are incorporated by reference.

Government Support

This invention was made with U.S. government support under W-7405-ENG-36, subcontract 10759-001-59 and DE-AC03-76SF00098 awarded by the Department of Energy. The U.S. Government has certain rights in the invention.

Background of the Invention

Research on charge transport in organic semiconductors is motivated by a variety of applications. The processing characteristics and demonstrated performance of known organic semiconductors suggest that they can be competitive for existing or novel applications requiring large-area coverage, structural flexibility, low-temperature processing, and, especially, low cost. There is a wide interest in finding new high performance, air-stable organic semiconductors with high charge transport capabilities for applications in the fields of organic-fϊeld-effect transistors (OFETs), organic photovoltaic cells, and organic light-emitting diodes (OLEDs). Organic semiconductors presently utilized in these devices have specific desirable electronic characteristics. By examining the physical origins of these electronic characteristics, other molecules with improved performance can be designed.

Charge Mobilities in Semiconductors

The defining electronic characteristic of an organic semiconductor is its charge mobility. This property, in turn, influences the diffusivity of charge carriers (electrons or holes) within the material and the electrical conductivity of the semiconductor as a whole. In inorganic semiconductors such as Si and Ge, the atoms are held together with very strong covalent bonds, which for the case of Si have energies as high as 76 kcal moP¹. In these semiconductors, charge carriers move as highly delocalized plane waves in wide bands and have a very high mobility, as mentioned above (μ »1 cm² V^"1 s^"1). Mobility is limited due to the scattering of carriers by lattice vibrations, and thus is reduced as temperature increases. On the other hand, the upper limits in microscopic mobilities of organic molecular crystals, determined at 300 K by time-of-flight experiments, fall between 1 and 10 Cm²V^-1S^"1. The weak intermolecular interaction forces in organic semiconductors, most usually van der Waals interactions with energies smaller than 10 kcal moP¹, may be responsible for this limit, since the vibrational energy of the molecules reaches a magnitude close to that of the intermolecular bond energies at or above room temperature.

Two kinds of transport are available in electronic materials that distinguish them from insulating materials: band transport and carrier transport ("hopping"). The boundary between band transport and hopping is defined by materials having mobilities between 0.1 and 1 Cm²V ¹S ¹. Highly ordered organic semiconductors, such as several members of the acene series including anthracene and pentacene, have room-temperature mobilities in this intermediate range. In some cases, temperature -independent mobility has been observed, even in polycrystalline thin films of pentacene. That observation was used to argue that a simple temperature-activated hopping mechanism can be excluded as a transport mechanism in high-quality thin films of pentacene. At low temperatures (below approximately 250 K), band transport becomes the mechanism that takes control of carrier transport in single crystals of pentacene and other acenes. Very high mobility values (from 400 Cm²V ¹S ¹ to more than 1000 Cm²V^{^1}S^"1) have been reported. At these temperatures, the vibrational energy is much lower than the intermolecular bonding energy and phonon scattering is very low; thus, high mobility is exhibited. At or close to room temperature, phonon scattering becomes so high that the contribution of the band mechanism to transport becomes too small. At these same temperatures, hopping begins to contribute to carrier transport. Hopping of carriers from site to site becomes easier as the temperature rises. The combination of these two mechanisms explains the fact that the mobility decreases as temperature rises from a few degrees K to about 250 K, and after that the mobility begins to rise slowly.

Computationally, hole mobility (μ₊) can be estimated by a Marcus-theory-based hopping transport model. To briefly summarize, according to Marcus theory, at temperature that is sufficiently high such that vibrational modes may be treated classically, the hole transfer rate between a dimer of two neighboring identical molecules is given in terms of the hole reorganization energy, λ₊, as

where kβ is the Boltzmann constant and T is the temperature. The hole coupling matrix element, V₊, is given as the energy splitting of the two highest-occupied molecular orbitals of the neutral dimer, V₊ = {EH_OM_O-EH_OM_O-I)!^- This is the lowest level in a hierarchy of increasingly detailed calculations which can include contributions of non-orthogonality and charge-induced polarizations. The hopping rates, W₁, between each of the various nearest neighbors, may be used to calculate the hole diffusion coefficient,

where n = 3 is the dimensionality, W₁ is the hopping rate to due charge transfer to the z-th neighbor at a distance of r_u and P₁ is the relative probability for charge transfer to a particular neighbor,

From the Einstein relation, the hole mobility is given as

kj ⁺ where e is the electron charge.

Exemplary Applications

p-channel Organic Field Effect Transistors (OFETs)

Organic field effect transistors comprise two electrodes (a source electrode and a drain electrode) in contact with the semiconductor, and an electric current flowing between the electrodes ("channel"), which is controlled by a voltage applied to a third electrode ("gate"). The gate electrode is constructed merely to apply an electric field to the semiconductor layer, whereby an electric current will not basically flow, and it is called a field effect transistor. In an OFET, the electric field of a gate electrode is utilized to modify the movement of charge by carrier entities through an organic layer between source and drain electrodes. If the carrier is a hole, this is referred to as a "p-channel" (for positive) device, if the carrier is negative, the device is called "n-channel" (negative). The mobility refers to the rate of a charge carrier to move between the source and drain electrodes through the material, under a given applied electric field. When charges or holes are injected from the source electrode, there is no external drain current measured for a period of time of

τ_d = L/μE , where L is the channel length, μ is the mobility, and E is the effective lateral electric field. Shorter values of τ_</ mean that the transistor can be switched between the "on" and "off" states more quickly, thus allowing for faster logic operations. Due to the types of manufacturing procedures, it is difficult to decrease L below 1-5 μm, and in addition, the use of high values of E can be both uneconomical (requiring expensive support circuits to generate such a high electric field from a low voltage supply (e.g., in a battery operated device)) and can ultimately lead to damage to the device, so it cannot be increased arbitrarily high. Therefore, the way to improve the operational speed of these devices is to increase μ and therefore decrease τ_</.

Presently, the organic semiconductors pentacene and tetracene have been used in OFETs. High hole mobilities in OFETs of up to 3.0 and 5.5 Cm²V ¹S ¹ have been reported for pentacene. However, due to the inherent chemical instability of pentacene, which readily undergoes many types of disproportionation reactions to generate impurities that decrease the mobility, devices made with this organic semiconductor are unstable under ambient conditions.

In addition to tetracene and pentacene, the molecule dinaptho[2,3-b:2',3'- f]thiopheno[3,2-b]thiophene (1, Figure 1) is known to have high hole mobility (2.1-2.9 Cm²V^-1S^"1) in a thin-film transistor setting and is stable in air. From a practical standpoint, the increased stability is a significant improvement over pentacene.

Radio Frequency IDentification (RFID)

Radio Frequency IDentification (RFID) tags are widely used in applications such as embedding into US Passports, "EZ-Pass"-style traffic charging, and inventory management. Of particular interest are "passive" devices, which do not require an integral power supply. Although, at present, these can be made with amorphous silicon, it would be more economical to produce these from organic semiconductors.

The most common RFID frequencies are 13.56 MHz (ISO 14443, ISO 15693, ISO 18000-3), followed by 125 kHz (ISO 18000-2), 900 MHz (ISO 18000-6), and 2.45 GHz (ISO 18000-4). Since the time period for a 13.56 MHz sinusoidal wave to go between zero and peak is 18.4 ns, τ_</ should be shorter than this. It has been experimentally demonstrated that this can be achieved with pentacene-based devices, although the input-output efficiency is less than 20% at this frequency.

Organic Photovoltaics (OPV)

Heterojunction bilayers formed by the interface of tetracene and Ceo have been demonstrated to act as photovoltaic devices with efficiency of 2.2%. Similarly, pentacene/Cβo bilayer devices have been demonstrated with efficiencies of 1.5%. In addition to potentially lower production costs than traditional silicon photovoltaics, these types of devices lend themselves to creating flexible photovoltaics.

Experimental measurements have indicated that poor hole mobility in the tetracene phase is a limiting factor in the efficiency of these devices. The low mobility results in the holes having more time in which they can recombine with the separated electrons, thus "wasting" the previously absorbed photon.

Summary of the Invention

One aspect of the present inventions relates to compounds structurally-related to thiophene that are calculated to have high hole mobilities. These molecules comprise extended π-electron systems and have utility as organic semiconductor materials. Additionally, they are stable in air. A second aspect of the invention relates to using these compounds in a variety of devices. Devices that suffer from poor efficiency would benefit from the use of these materials. They include, but are not limited to, organic field effect transistors, radio frequency identification devices, and organic photovoltaic devices. Brief Description of the Figures

Figure 1 depicts the structure of dinaptho[2,3-b:2',3'-f]thiopheno[3,2-b]thiophene (I)-

Figure 2 depicts the library constructed by substituting fragments 1* or A-F to the [:4,5]thieno[2,3-d]thiophene core (top left).

Figure 3 depicts the structure of anthra[2,3-b]anthra[2',3':4,5]thieno[2,3- d]thiophene (2).

Figure 4 depicts the structure of pyreno[l,2-b]pyreno[2',l':4,5]thieno[2,3- d]thiophene (7).

Detailed Description of the Invention

A number of compounds (Figure 2) structurally related to 1 (Figure 1) have been examined using a combination of density-functional theory, molecular mechanics crystal structure predictions, and Marcus theory charge transport models. Specifically of interest are anthra[2,3-b]anthra[2',3':4,5]thieno[2,3-d]thiophene (2) (Figure 3) and pyreno[l,2- b]pyreno[2',l':4,5]thieno[2,3-d]thiophene (7) (Figure 4), which have been calculated to have hole mobilities up to three times that of 1 and twice as high as pentacene. The hole mobilities of the these compounds are predicted to be 9.8 and 3.2 cm²/Vs, respectively. Additionally, these compounds will be stable in air. The high mobility of 2 will cause it to have applications, for example, in organic field effect transistors (OFETs). Moreover, analysis of the HOMO levels of 2 and 7 indicates that these molecules can also, for example, be substituted for tetracene in C60/tetracene/PEDOT:ITO organic heterojunction photo voltaics, where the air stability and greatly improved hole mobilities will dramatically increase the performance of these devices. Additionally, these molecules proved to have lower hole reorganization energies than pentacene. These fused thiophenes can further be functionalized, for example with alkyl groups, to yield solution-processable molecules with similarly predictable electronic properties. Also, substitution of other atoms for sulfur, including but not limited to the electronically-related selenium atom, often proves to impart similar electronic characteristics to compounds of interest. Computational Methods: Comparison of Extended π-Systems

Hole Reorganization Energies, λ₊

Geometries of the singlet ground state, lowest triplet states, doublet radical cations and anions of the molecules in Figure 2 were optimized at the B3LYP/6-31G(d) level of theory, followed by single -point calculations employing the valence-triple- ζ 6- 311+G(d,p) basis set. Tight convergence criteria for gradients were used throughout. This approach gave good agreement with experimental reorganization energies, ionization potentials, electron affinities, and the experimental values for polyacenes. In general, it is known that DFT methods typically give reorganization energies comparable to second- order Moller-Plesset (MP2) calculations, and recent benchmark calculations against experimental polyacene data suggest that this approach describes the qualitative behavior of the reorganization energy and ionization potential. Although it has been suggested that HOMO and LUMO eigenvalues may be empirically shifted (with a linear expression) to better match experimental values, this approach was not used in the calculations described. The calculated reorganization energies are shown in Table 1 and can be described as follows: the reorganization energy X₊ (X.) for hole (electron) transport is calculated as the sum of the energy required for reorganization of the vertically ionized neutral to cation (anion) geometry, X₂ (/U), plus the energy required to reorganize the cation (anion) geometry back to the neutral equilibrium structure on the ground state potential energy surface, Xi (/Lj). These calculations were performed using Gaussian03, Revision C.02

1 0 .068 0 .060 0 .114 0 .086 0 .128 0 .200

2 0 .045 0 .040 0 .082 0 .056 0 .084 0 .138

3 0 .095 0 .093 0 .122 0 .085 0 .188 0 .206

4 0 .094 0 .094 0 .121 0 .092 0 .188 0 .213

5 0 .094 0 .087 0 .121 0 .088 0 .181 0 .209

6 0 .064 0 .057 0 .079 0 .053 0 .121 0 .132

7 0 .038 0 .037 0 .066 0 .041 0 .075 0 .107

8 0 .072 0 .066 0 .094 0 .068 0 .138 0 .162

Table 1. Reorganization energies (in eV).

Because these molecules have potential in this area, the focus will be on the hole reorganization energies, λ₊. Table 1 shows that 3-5 have X₊ ~ 50 meV greater than 1, comparable to that of naphthalene (X₊ = 0.183 eV). From this data, it can be inferred that these will have inferior carrier mobilities to 1. In contrast, 6 has λ₊ comparable to that of 1, and 2 and 7 have λ₊ 44 and 53 meV lower (respectively) than that of 1, and moreover, lower than pentacene (λ₊ = 0.092-0.099 eV). Both 2 and 7 are shown to have lower hole reorganization energies than those of both 1 and pentacene.

Crystal Structure Prediction

The crystal structures, based on rigid-body unit-cell optimization of the calculated gas phase structure of 1, were optimized using the Dreiding force field, which is suitable for this purpose when used in conjunction with charges calculated with a high level ab initio theory. The optimization algorithm used was a combination of steepest descent, Newton- Raphson and quasi-Newton methods. A unit cell was optimized with periodic boundary conditions where long-range interaction energies were calculated by Ewald sums. For the crystal structures, P 2\ symmetry was imposed. For molecule 1, the initial guess for the optimization was the experimentally-determined unit cell. The results presented are based on a lattice energy minimization of motionless molecules, i.e., finite temperature effects were totally neglected. The appropriate point charges were calculated by a fit to the electrostatic potential (ESP). The effect of charges calculated by B3LYP/6-311+G(d,p) and PBE/DNP levels of theory on the unit cell parameters are shown in Table 2. Both yielded comparable structure parameters to the experimentally-determined unit cell, although B3LYP/6-311+G(d,p) charges had slightly better agreement with the experimental unit cell parameters and density. Because of the similarities in the structures of 2 and 7 to the molecule 1, the initial guess of the unit cell parameters from 1 was modified in accordance with the sizes of molecules 2 and 7, then the optimization as described above was performed using the B3LYP/6-311+G(d,p) ESP charges. All crystal prediction calculations were carried out with the Materials Studio Modules, Forcite and DMoI.

1 (xtal) 1 (DNP) l(G) 2 7 space group P2i P2i P2i P2i P2i

A(A) 6.187(4) 6.401 6.3559 6.4435 8.6519

B(A) 7.662 (6) 7.648 7.5778 7.6217 7.1976

C(A) 16.21(1) 16.499 16.2267 21.2032 19.6007 α (deg) 90 90 90 90 90 β (deg) 92.49 (2) 93.24 92.67 89.24 91.487 γ (deg) 90 90 90 90 90 cell volume (A³) 767.706 806.331 780.687 1041.21 1220.18

Table 2. Cell parameters used in the calculation of the coupling matrix elements and transport properties of

Table 5.

Electronic Properties

As shown in Table 3, the calculated HOMO energy of 1 is in excellent agreement with the electrochemically-defϊned cyclic voltametry measurement of 5.44 eV. The calculated HOMO-LUMO gap is in reasonable agreement with the optically-observed absorption edge of 3.0 eV, given that the calculation considers an isolated molecule in vacuum, whereas the experiment was performed on a crystal.

The relative stability in air of the molecules may be rationalized by the higher Δε =

3.306 eV, and lower lying S_HOMO = -5.479 eV for 1, as compared to Δε = 2.176 eV and S_HOMO = -4.937 eV for pentacene. While pentacene has an observed p-channel FET mobility of 3-7 cm²/Vs, the reported p-channel FET mobility of 1 was observed to be 2.1- 2.9 cm²/Vs under the optimized preparation. This can be rationalized by the larger hole reorganization energy λ₊ = 0.128 eV for 1, as compare to/I ₊ = 0.092 eV and λ ₊ = 0.099 eV calculated for pentacene.

Having established an approach to estimating electronic properties with 1, larger ring structures, such as 2-8, were then examined. Specifically, the desired physical properties of (a) greater stability (i.e., greater Δε, comparable or lower S_HOMO) and (b) lower λ₊, in comparison with 1, were probed for the purpose of yielding, for example, higher- performance OFET devices. Increasing the length of polyacenes leads to a decreasing Δε, λ_±, IE, and to increasing EA, so that a decrease in stability cancels any benefit from reduced λ_±. However, as shown in Table 3, molecules 3, 4, 5, and 7 all have larger Δε than 1. Given the inaccuracies of the gaps calculated by DFT in general and B3LYP in particular, 6, which had a value only 53 meV lower than 1, may also be considered comparable to 1. In addition, 3-7 had lower S_HOMO than that of 1, adding support for their environmental stability. In contrast, both 2 and 8 had gaps that are lower than that of 1 by ~ 0.5 eV, with calculated gaps between those of tetracene (Δε = 2.737 eV) and pentacene (Δε = 2.116 eV), and with SH_OM_O comparable to tetracene (SH_OM_O ⁼ 5.199). SHOMO SL UMO Δε ΔE ST, vert ΔEsT.aώa

1 -5.479 -2.173 3 .306 2.232 1.964

2 -5.174 -2.567 2 .608 1.683 1.484

3 -5.746 -1.911 3 .834 2.821 2.500

4 -5.628 -1.980 3 .648 2.564 2.245

5 -5.634 -2.007 3 .627 2.607 2.278

6 -5.482 -2.288 3 .253 2.308 2.052

7 -5.512 -2.078 3 .434 2.591 2.420

8 -5.224 -2.460 2 .764 1.909 1.662

Table 3. Energies (in eV) of the HOMO, HOMO-LUMO gap, adiabatic energies, and electron affinities, and singlet-triplet energy splitting.

Table 4 shows that the IE of 3-5 are greater than that of 1, and that the IE of 6 and 7 are lower than that of 1. However, in all cases these values are still 0.3-0.5 eV greater than the IE of pentacene (IE_vert = 6.229 eV, IE_adia = 6.185 eV). Table 4 also depicts the EA of these compounds: those of 3-5 are lower than 1 by 0.1 eV, and those of 6 and 7 greater than that of 1 by 0.1 and 0.2 eV, respectively. None of 1-8 has an EA high enough for use as n-channel materials (efficient electron injection from common metal electrodes requires EA of 3-4 eV).

lEvert lactam EA_vert

1 6.738 6.678 0.965 1.050

2 6.262 6.223 1.528 1.584

3 6.885 6.792 0.823 0.907

4 6.790 6.696 0.849 0.941

5 6.786 6.699 0.888 0.976

6 6.582 6.525 1.159 1.212

7 6.582 6.545 1.042 1.083

8 6.297 6.231 1.415 1.482

Table 4. Vertical and adiabatic ionization energies and electron affinities (in eV).

Hole Mobility, μ_Λ The hole mobility, μ₊, was calculated following a Marcus-theory-based hopping transport model, as described previously. Although this approach neglects tunneling contributions to the mobility, which can significantly increase the hole mobility of highly purified polyacenes, especially at low temperatures, a goal of the calculation was to obtain a lower bound of the performance of the materials in the presence of impurities, polymorphism, and temperature effects, which lead to carrier localization best described by a hopping model.

To aid comparison with the previous work on pentacene, only nearest neighbor hopping was considered (to two different types of transverse dimers, one type of parallel- oriented dimer, and one longitudinally oriented dimer), and only the inner sphere contribution (resulting from relaxation of the molecular geometry due to charging) to the reorganization energies was considered. Also, only a single minimum energy crystal structure in the evaluation of V was considered, and T = 300 K was used. Previous studies on pentacene have indicated that the finite temperature motion of the dimers leads to an increase in the average mobility. Therefore, the results presented should be understood as a conservative lower estimate on the hopping mobility.

To obtain a numerical estimate of the hole mobility, the experimental crystal structure of 1 was used to calculate the HOMO coupling parameters, V₊, for the four types of dimers. The results, as well as a comparison to the comparable values calculated for pentacene, are shown in Table 5. In general, the coupling matrix elements of 1 are comparable to, or slightly larger than, those of pentacene. However, a lower diffusion coefficient and drift mobility of 1 results from the higher λ₊, due to the exponential dependence of the transfer rate on this parameter in the Marcus rate expression.

pentacene 1 (petal) 1 (DNP) 1 (G) 2 7 dτi (A) 4.734 4.886 5.025 4.953 4.984 5.617

Vn (eV) 0.137 0.1687 0.1586 0.1459 0.1630 0.0671 d_T2 (A) 5.199 5.148 5.284 5.219 5.273 5.644

VT₂ (eV) 0.120 0.1336 0.1350 0.1208 0.1427 0.0761 dp (A) 6.253 6.187 6.401 6.356 6.444 7.198

VP (Q\) 0.006 0.0747 0.0569 0.0605 0.0495 0.00068 d_L (A) 14.10 16.21 16.499 16.227 21.203 19.601 V_L (eV) 0.0008 0.00258 0.00122 0.00095 0, .00082 0, .0061

D₊ (cm²/s) 0 .138 0 .126 0 .125 0 .0999 0, .254 0. ,0816 μ₊ (Cm²V^"1 5 .37 4 .89 4 .82 3 .86 9, .81 3. .16

Table 5. Structural and hole transport properties of selected molecules, with hole mobility, μ₊, calculated at

300 K. Results for 1 include the experimental crystal structure ("xtar), and the calculated results using PBE/DNP charges ("DNP") and B3LYP/6-311+G(d,p) charges ("G"). Results for 2 and 7 were calculated using B3LYP/6-3 l l+G(d,p) charges.

The hole mobility results based on the calculated crystal structures of compounds 2 and 7 are also shown in Table 5. As with pentacene and 1, both 2 and 7 show highly anisotropic mobility, with the strongest couplings between the two pairs of transverse dimers. In the case of 2, the nearest-neighbor distances are comparable, and the transverse couplings slightly stronger than those of 1. In the case of 7, however, despite the much lower λ₊, the transverse dimer couplings are weakened, leading to μ₊ slightly smaller than that of 1.

Charge transport modeling indicates that 2 will have a hole mobility of 9.8 Cm²V ¹S \ twice that of 1. This high mobility, combined with the stability in air demonstrated for this family of molecules, is promising for applications such as high- performance OFETs. In addition, since 2 has similar HOMO energy to tetracene, but with dramatically higher predicted hole mobility, it may be utilized to improve the hole-mobility limited performance of tetracene/Cβo hetero-junction photovoltaics among other devices.

Exemplary Applications of the Present Invention

All of the applications discussed below result from (a) the higher mobility of charges in these materials (as compared to, e.g., pentacene), and (b) the greater stability of these materials under environmental conditions (again, as compared to, e.g., pentacene).

p-channel Organic Field Effect Transistors (OFET)

Experimental examination of 1, as well as calculations of 1, 2, and 7 indicated that these (like pentacene) will be useful as a p-channel material. As described previously, the operational speed of OFET devices would be greatly improved if the mobility (μ) were increased from that calculated for pentacene-based devices. The highest hole mobilities obtained for pentacene thin-film transistors (TFTs) grown by both organic vapor phase deposition (OPVD) and vacuum thermal evaporation (VTE) are μ ~ 1.5 Cm²V^-1S^"1. In contrast, vacuum deposition of 1 was found to give hole mobilities of μ ~ 2 - 3 Cm²V^-1S^"1. The calculations suggest that there is an ideal upper bound for 1 (μ ~ 4.9 Cm²V^-1S^"1). The calculations indicate that 2 should have μ ~ 9.8 Cm²V^-1S^-1 and 7 should have μ ~ 3.1 cm²V ¹S \ Due to the structural similarity between 1, 2, and 7, the efficiency of vacuum deposition should be similar. Thus, 2 is expected to give devices which can operate 2-3 times faster than 1 and 4-6 times faster than the current pentacene devices. The expected performance improvement of 7 is a more modest 2 times speedup over pentacene devices.

Besides mobility, another important characteristic is environmental stability in air. Pentacene undergoes numerous disproportionation reactions, which substantially reduce the device performance. As a result, a barrier layer must be added, increasing the cost of the device. In contrast, the mobility of 1 was found to be unaffected by air. The calculations indicate that the same should be true of 2 and 7. As a result, materials made with these molecules will be longer-lasting and less expensive to manufacture than pentacene-based devices, in addition to the very favorable performance characteristics discussed above.

Radio Frequency IDentification (RFID)

As previously mentioned, one of the most common RFID frequencies is 13.56 MHz (ISO 14443, ISO 15693, ISO 18000-3). Since the time period for a 13.56 MHz sinusoidal wave to go between zero and peak is 18.4 ns, τ_</ should be shorter than this. Use of a higher-mobility material, such as 2 or 7, would enable the utilization of higher frequencies and/or would allow for greater efficiency. The importance of greater efficiency is that it allows for lower-powered (and therefore more lightweight and/or longer-battery life) "reader" devices and/or a greater operational distance between the RFID tag and the reader device.

In addition, the environmental stability discussed in the previous section is advantageous in this regard as well, and would contribute to even lower RFID tag costs, due to the simplification or elimination of the atmospheric barrier.

Organic Photovoltaics (OPV)

Tetracene- and pentacene-based photovoltaic devices suffer from poor efficiency due to their low hole mobility. Higher mobility allows the holes to more quickly move to the electrode where they can be utilized. Since the HOMO energies of 2 and 7 are within ± 25 meV that of tetracene, either of these may be used as a substitute for tetracene in these types of devices without requiring any changes in the type of electrode contact materials. Additionally, the ITO/PEDOT:PSS (indium tin oxide/poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate), a known organic semiconductor) interface has a work function of 5.2 eV. Therefore, 7 may be a suitable alternative for this organic semiconductor, as it has both a suitable S_HOMO, as well as λ₊ 36 meV lower than tetracene. Additionally, 2 is predicted to have a lower band gap than tetracene, enabling it to absorb more of the visible light which is presently wasted by tetracene, if it is desired that light be absorbed in both components of the heterojunction. On the other hand, if the light is only desired to be absorbed in the Ceo phase, 7 is predicted to be relatively transparent to visible light. The greater hole mobility of both 2 and 7, as compared to tetracene or pentacene, will lead to improved device efficiency. Finally, the greater environmental stability in air of 2 and 7, as compared to tetracene or pentacene, is expected to help improve the lifetime of the final photovoltaic device.

Definitions

As used herein, the terms "a", "an", and "the" are used interchangeably with "at least one" to mean one or more of the elements being described.

As used herein, the term "acene" refers to a polycyclic aromatic hydrocarbon group having at least 2 fused benzene rings in a rectilinear arrangement.

As used herein, the term "acenyl" refers to a monovalent radical of an acene. The acenyl group usually has 2 to 4 fused benzene rings in a rectilinear arrangement. Exemplary acenyl groups include naphthyl, anthracenyl, and tetracenyl.

The term "alkyl" refers to a hydrocarbon chain that may be a straight chain or branched chain, containing the indicated number of carbon atoms. For example, C₁-C₁₂ alkyl indicates that the group may have from 1 to 12 (inclusive) carbon atoms in it. Alkyl groups may be optionally inserted with O, N, or S.

The term "alkenyl" refers to a straight or branched hydrocarbon chain containing 2-

8 carbon atoms and characterized in having one or more double bonds. Examples of a typical alkenyl include, but not limited to, allyl, propenyl, 2-butenyl, 3-hexenyl and 3- octenyl groups. The term "alkynyl" refers to a straight or branched hydrocarbon chain containing 2-8 carbon atoms and characterized in having one or more triple bonds. Some examples of a typical alkynyl are ethynyl, 2-propynyl, and 3-methylbutynyl, and propargyl. The sp² and sp³ carbons may optionally serve as the point of attachment of the alkenyl and alkynyl groups, respectively.

The term "alkoxy" refers to an -O-alkyl radical.

The term "aryl" refers to an aromatic monocyclic, bicyclic, or tricyclic hydrocarbon ring system, wherein any ring atom can be substituted. Examples of aryl moieties include, but are not limited to, phenyl, naphthyl, anthracenyl, and pyrenyl.

The term "heteroaryl" refers to an aromatic 5-8 membered monocyclic, 8-12 membered bicyclic, or 11-14 membered tricyclic ring system having 1-3 heteroatoms if monocyclic, 1-6 heteroatoms if bicyclic, or 1-9 heteroatoms if tricyclic, said heteroatoms selected from O, N, or S (e.g., carbon atoms and 1-3, 1-6, or 1-9 heteroatoms of N, O, or S if monocyclic, bicyclic, or tricyclic, respectively), wherein any ring atom can be substituted.

The term "acyl" refers to an alkylcarbonyl, cycloalkylcarbonyl, arylcarbonyl, heterocyclylcarbonyl, or heteroarylcarbonyl substituent, any of which may be further substituted by substituents.

The term "substituents" refers to a group "substituted" on an alkyl, cycloalkyl, alkenyl, alkynyl, heterocyclyl, heterocycloalkenyl, cycloalkenyl, aryl, or heteroaryl group at any atom of that group. Suitable substituents include, without limitation, alkyl, alkenyl, alkynyl, alkoxy, halo, hydroxy, cyano, nitro, amino, SO₃H, sulfate, phosphate, perfluoroalkyl, perfluoroalkoxy, methylenedioxy, ethylenedioxy, carboxyl, oxo, thioxo, imino (alkyl, aryl, aralkyl), S(O)_nalkyl (where n is 0-2), S(O)_n aryl (where n is 0-2), S(O)_n heteroaryl (where n is 0-2), S(O)_n heterocyclyl (where n is 0-2), amine (mono-, di-, alkyl, cycloalkyl, aralkyl, heteroaralkyl, and combinations thereof), ester (alkyl, aralkyl, heteroaralkyl), amide (mono-, di-, alkyl, aralkyl, heteroaralkyl, and combinations thereof), sulfonamide (mono-, di-, alkyl, aralkyl, heteroaralkyl, and combinations thereof), unsubstituted aryl, unsubstituted heteroaryl, unsubstituted heterocyclyl, and unsubstituted cycloalkyl. In one aspect, the substituents on a group are independently any one single, or any subset of the aforementioned substituents.

Aspects of the Present Invention

An embodiment of the invention is a compound of formula I:

Formula I

wherein, independently for each occurrence,

R is C^a and R' is C in a ring system selected from the group consisting of:

R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, and R¹¹ are selected from the group consisting of H, OH, halide, alkyl, alkoxy, aryl, heteroaryl, alkenyl, alkynyl, CN, acyl, and aryloxy;

at least one of R , 10 and R 11 is H; and

X is selected from the group consisting of S, Se, O, and NR 12 ;. and

R . 12 is selected from the group consisting of H and alkyl.

In certain embodiments, X is S.

In certain embodiments, R and R' are represented by

(A)

In another embodiment, R and R' are represented by

In certain embodiments, the invention relates to a compound of formula I, wherein R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, and R¹¹ are H.

In certain embodiments, the invention relates to a compound of formula I, wherein X is S; and R and R' are represented by

(A)

In another embodiment, the invention relates to a compound of formula I, wherein X is S and R and R' are represented by

In one embodiment of the invention, X is S; R and R' are represented by

and R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, and R⁹ are H in a compound of formula I. In another embodiment of the invention, X is S; R and R' are represented by

(F)

and R >2 , r R>3 , _π R4 , _π R5 , _π R6 , _π R7 , _π R8 , and R are H in a compound of formula I.

One embodiment of the invention relates to a compound of formula II:

Formula Il

wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵, and R¹⁶ are independently selected from the group consisting of: H, OH, halide, alkyl, alkoxy, aryl, heteroaryl, alkenyl, alkynyl, CN, acyl, aralkyl, and aryloxy.

An embodiment of the invention is a compound of formula II, wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵, and R¹⁶ are H.

One embodiment of the invention is a compound of formula III:

wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵, and R¹⁶ are independently selected from the group consisting of: H, OH, halide, alkyl, alkoxy, aryl, heteroaryl, alkenyl, alkynyl, CN, acyl, aralkyl, and aryloxy.

An embodiment of the invention is a compound of formula III, wherein R 1 , r R> 2 , _π R3 , R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵, and R¹⁶ are H.

In certain embodiments, the invention is a compound of formula IV:

Formula IV

In another embodiment, the invention is a compound of formula V:

In certain embodiments, the present invention involves a semiconductor comprising a compound of formula I, formula II, formula III, formula IV, or formula V.

In certain embodiments, the invention relates to a field effect transistor comprising a semiconductor of the present invention.

In another embodiment, the invention relates to a radio frequency identification device comprising a semiconductor of the present invention. In yet another embodiment, the invention relates to a photovoltaic device comprising a semiconductor of the present invention.

Exemplification The invention now being generally described, it will be more readily understood by reference to the following examples, which are included merely for purposes of illustration of certain aspects and embodiments of the present invention, and are not intended to limit the invention.

Example 1 Procedure for Preparation of Anthra[23-b]anthra[2\3':4,51thieno[2,3-d]thiophene (2) (or dianthracen-r2.3:4\5'lthienor2.3-dlthiophene (DATT))

Compounds AS-I through AS-4 were prepared according to procedures reported by Arjunan et ah: Arjunan, P.; Berlin, K. D. An improved synthesis of 2-anthraldehyde. Organic Preparations and Procedures International 1981, 13(5), 368-71.

Compounds AS-5, AS-6, and DATT were prepared using protocols analogous to those reported by Yamamoto, et al: Yamamoto, T.; Takimiya, K. Facile Synthesis of Highly π-Extended Heteroarenes, Dinaphtho[2,3-b:2',3'-fjchalcogenopheno[3,2- b]chalcogenophenes, and Their Application to Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 2224-2225.

Preparation of 2-anthroic acid, AS-I. A suspension of AS-O (10 g, 40 mmol), zinc dust (30 g), CuSO₄ (0.5 g), and aqueous ammonia (20%, 300 mL) was added to a 500-mL round-bottomed flask equipped with a condenser and a magnetic stirrer. The reaction mixture was stirred at 70 ⁰C for 3 h. The resulting amber solution was filtered while still hot, cooled to 25 ⁰C, and acidified with dilute HCl (1 :1, 400 mL) to obtain a yellow precipitate. The solid was dried, recrystallized from acetic acid to yield 6.8 (75%) of AS-I as a yellow powder. ¹H NMR (DMSO-d₆): δ 8.76 (2H, s), 8.62 (IH, s), 8.11 (4H, m), 7.57 (2H, m).

Preparation of ethyl-2-anthroate, AS-2. A mixture of AS-I (4.9 g, 22 mmol), anhydrous ethanol (150 mL), and concentrated H₂SO₄ (7 mL) was refluxed for 24 h. The resulting suspension was cooled to room temperature and the solvent was evaporated under reduced pressure to yield a yellow solid. The solid was dissolved in diethyl ether and washed with water and aqueous sodium carbonate. Recrystallization of this precipitate from ethanol yielded 4.3 g (79%) of AS-2 as white flakes. ¹HNMR (DMSO-d₆): δ 8.85 (2H, s), 8.68 (IH, s), 8.18 (3H, m), 7.96 (IH, m), 7.61 (2H,m), 4.42 (2H, q), 1.42 (3H,t). Preparation of 2-hydroxymethylanthracene, AS-3. Into a round-bottomed flask equipped with an addition funnel, a water cooled condenser, and a magnetic stirrer were placed 8 mL of a 2.0 M solution Of LiAlH₄ in THF (16 mmol) and 100 mL of dry ether. A solution of AS-2 (2 g, 7.93 mmol) in ether (200 mL) was placed into the addition funnel and added dropwise to the LiAlH₄ suspension over 10 minutes. The resulting suspension was stirred at 40 ⁰C for 3 h and then cooled to room temperature; the excess LiAlH₄ was consumed by addition of ethyl acetate (100 mL). Water was then added to the reaction mixture; the organic layer was separated and washed with water (2x100 mL). The ethyl acetate solution was evaporated under reduced pressure to yield a yellow solid (AS-3 A). The aqueous layer was evaporated and the remaining solid was rinsed with 500 mL of hot ethanol. The ethanol solution was evaporated and the resulting yellow solid (AS-3B) was combined with AS-3A to yield 1.5 g (90.3%) of AS-3. ¹HNMR (CDCl₃): δ 8.5-7.0 (9H, s), 4.94 (2H, s), 1.57 (IH, s).

Preparation of 2 -anthr aldehyde, AS-4. Pyridine (5 g, 60 mmol) and CH₂Cl₂ (70 mL) were added to a round-bottomed flask equipped with a rubber septum and a magnetic stirrer. The solution was stirred for 5 minutes before adding 3 g (30 mmol) Of CrO₃. The resulting suspension was stirred at room temperature for 30 minutes to yield a deep burgundy-colored solution. A suspension of AS-3 (1 g, 5 mmol) in 15 mL Of CH₂Cl₂ was then added to the mixture. A black, tarry residue separated immediately after the addition of AS-3 and the solution was stirred for an additional 15 minutes. The black residue was filtered off and washed with 200 mL of ethyl ether. The combined organic layers (ether and CH₂Cl₂) were washed successively with 5% aq. NaOH (3x100 mL), 5% aq. HCl

(3x100 mL), 5% aq. NaHCO₃ solution (3x100 mL), and finally with 100 mL brine. The resulting solution was evaporated and dried over magnesium sulfate to yield a dark yellow solid which turned brick-red upon exposure to light. The product was therefore stored away from light and recrystallized from toluene to give 0.8 g (80%) of AS-4 as a dark yellow powder. ¹HNMR (DMSO-d₆): δ 8.78 (4H, s), 8.26 (2H, s), 7.78 (4H, m).

Preparation of 3-methylthio-2-anthraldehyde, AS-5. In a well-ventilated fume hood with disposable gloves, butyllithium (13.2 mL of 1.59 M solution in hexane, 21.0 mmol) was added to a solution of jV,jV,iV-trimethylethylenediamine (2.87 mL, 21.0 mmol) in THF

(35 mL) at -30 ⁰C. After the mixture was stirred for 15 min at the same temperature, a solution of 2-anthraldehyde (2.66 g, 12.8 mmol) in THF (20 mL) was slowly added over a period of 5 min, and then additional butyllithium (24.15 rnL of 1.59 M solution in hexane, 38.4 mmol) was added, and the resting mixture was stirred for 3.5 h at -30 ⁰C. Excess dimethyl disulfide (5.67 mL, 64 mmol) was then added, and after stirring at room temperature for 2 h, 1 M hydrochloric acid (20 mL) was added. The resulting mixture was stirred for 10 h and was extracted with dichloromethane (20 mL x 3). The combined extracts were dried (MgSO₄) and concentrated in vacuo. The residue was purified by column chromatography on silica-gel eluted with hexane-ethyl acetate.

Preparation of trans- 1 ,2-bis(3-methylthio-2-anthracen-yl)ethene, AS-6. To an ice- cooled suspension of zinc powder (0.39 g, 6.0 mmol) in THF (10 mL), titanium tetrachloride (0.66 mL, 6.0 mmol) was slowly added, and the resulting mixture was refluxed for 1.5 h. After cooling to room temperature, a solution of AS-5 (2.0 mmol) in THF (10 mL) was slowly added to the mixture, and the mixture was then refluxed for 1O h. After cooling to room temperature, the mixture was diluted with saturated aqueous sodium hydrogen carbonate solution (30 mL) and dichloromethane (30 mL) and stirred for 3.5 h. The mixture was filtered through a Celite pad, and the filtrate was separated into an organic and an aqueous layers. The aqueous layer was extracted with dichloromethane (20 mL x 3), and the combined organic layers were dried (MgSO₄) and concentrated in vacuo. The resulting residue was purified by passing through a silica-gel pad eluted with dichloromethane to give AS-6 as orange crystals.

Preparation of anthra[2,3-b]anthra[2 ',3 ':4,5]thieno[2,3-d]thiophene (or dianthracen-[2,3-b:2',3'-f]thieno[3,2-b]thiophene), DATT, (2). A solution of AS-6 (0.60 mmol) and iodine (4.87 g, 19.2 mmol) in chloroform (15 mL) was refluxed for 21 h. After cooling to room temperature, saturated aqueous sodium hydrogen sulfite solution (20 mL) was added, and the resulting precipitate was collected by filtration and was washed with water and chloroform. The crude product was purified by vacuum sublimation (source temperature: 220 ⁰C under ~10^"3 Pa) to give an analytical sample of DATT (2) as an orange solid. Example 2

Procedure for Preparation of Pyreno[12-b1pyreno[2\r:4,5]thieno[2,3-d^"|thiophene (7) (or

(excess)

P-O P-I

Compounds P-I, P-2, and DPTT (7) were prepared using protocols analogous to those reported by Yamamoto, et al: Yamamoto, T.; Takimiya, K. Facile Synthesis of

Highly π-Extended Heteroarenes, Dinaphtho[2,3-b:2',3'-fjchalcogenopheno[3,2- b]chalcogenophenes, and Their Application to Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 2224-2225.

Preparation of l-methylthio-2-pyrenaldehyde, P-I. To a solution of N,N,N'- trimethylethylenediamine (2.87 mL, 21.0 mmol) in THF (35 rnL) was added butyllithium (13.2 mL of 1.59 M solution in hexane, 21.0 mmol) at -30 ⁰C. After the mixture was stirred for 15 min at the same temperature, a solution of 2-pyrenaldehyde (12.8 mmol) in THF (20 mL) was slowly added over a period of 5 min, and then additional butyllithium (24.15 mL of 1.59 M solution in hexane, 38.4 mmol) was added, and the resulting mixture was stirred for 3.5 h at -30 ⁰C. Excess dimethyl disulfide (5.67 mL, 64 mmol) was then added, and after stirring at room temperature for 2 h, 1 M hydrochloric acid (20 mL) was added. The resulting mixture was stirred for 1O h and was extracted with dichloromethane (20 niL x 3). The combined extracts were dried (MgSO₄) and concentrated in vacuo. The residue was purified by column chromatography on silica-gel eluted with hexane-ethyl acetate.

Preparation of trans-1 ,2-bis(l-methylthio-2-pyrenyl)ethene, P-2. To an ice-cooled suspension of zinc powder (0.39 g, 6.0 mmol) in THF (10 mL), titanium tetrachloride (0.66 mL, 6.0 mmol) was slowly added, and the resulting mixture was refluxed for 1.5 h. After cooling to room temperature, a solution of P-I (2.0 mmol) in THF (10 mL) was slowly added to the mixture, and the mixture was then refluxed for 1O h. After cooling to room temperature, the mixture was diluted with saturated aqueous sodium hydrogen carbonate solution (30 mL) and dichloromethane (30 mL) and stirred for 3.5 h. The mixture was filtered through a Celite pad, and the filtrate was separated into an organic and an aqueous layer. The aqueous layer was extracted with dichloromethane (20 mL x 3), and the combined organic layer was dried (MgSO₄) and concentrated in vacuo. The resulting residue was purified by passing through a silica-gel pad eluted with dichloromethane to give trans- l,2-bis(l-methylthio-2-pyrenyl)ethene as yellow crystals.

Preparation of pyreno[l,2-b]pyreno[2 ',l ':4,5]thieno[2,3-d]thiophene (or dipyren- [l,2-b:l ',2'-f]thieno[3,2-b]thiophene), DPTT, (7). A solution of P-2 (0.60 mmol) and iodine (4.87 g, 19.2 mmol) in chloroform (15 mL) was refluxed for 21 h. After cooling to room temperature, saturated aqueous sodium hydrogen sulfite solution (20 mL) was added, and the resulting precipitate was collected by filtration and was washed with water and chloroform. The crude product was purified by vacuum sublimation to give an analytical sample of DPTT (7) as a yellow solid.

Incorporation by Reference

All of the patents and publications cited herein are hereby incorporated by reference.

Equivalents

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.

Claims

We claim:

1. A compound of formula I :

Formula I

wherein, independently for each occurrence,

R is C^a and R' is C^b in a ring system selected from the group consisting of:

R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, and R¹¹ are selected from the group consisting of H, OH, halide, alkyl, alkoxy, aryl, heteroaryl, alkenyl, alkynyl, CN, acyl, and aryloxy;

at least one of R¹⁰ and R¹¹ is H; and

X is selected from the group consisting of S, Se, O, and NR¹²; and

R¹² is selected from the group consisting of H and alkyl.

2. The compound of claim 1, wherein X is S.

3. The compound of claim 1 , wherein R and R' are represented by

(A)

The compound of claim 1, wherein R and R' are represented by

5. The compound of claim 1, wherein τ

R-> 4⁴, τ

R-> 6, τ R-> 7', R⁸, R >9^y, „ R1¹0^U, and R , 1¹1¹ are H 6. The compound of claim 1, wherein X is S; and R and R' are represented by

1. The compound of claim 1 , wherein X is S; and R and R' are represented by

8. The compound of claim 2, wherein R and R' are represented by

and R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, and R⁹ are H.

9. The compound of claim 2, wherein R and R' are represented by

and R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, and R⁹ are H.

10. A compound of formula II :

Formula I I

wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵, and R¹⁶ are independently selected from the group consisting of H, OH, halide, alkyl, alkoxy, aryl, heteroaryl, alkenyl, alkynyl, CN, acyl, aralkyl, and aryloxy.

11. The compound of claim 10, wherein R ι l¹, r R>2, _n R6 R7', _n RS⁸ H

, _n , _n R9^y, „ R1¹0^U, r R> ¹¹, r R> 1¹2 R¹³, R¹⁴, R¹⁵, and R¹⁶ are H.

12. A compound of formula III :

wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵, and R¹⁶ are independently selected from the group consisting of H, OH, halide, alkyl, alkoxy, aryl, heteroaryl, alkenyl, alkynyl, CN, acyl, aralkyl, and aryloxy.

13. The compound of claim 12, wherein R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹²,

R , 1¹3^J, R 14 R¹⁵, and R¹⁶ are H.

14. A compound of formula IV :

Formula IV

15. A compound of formula V :

16. A semiconductor comprising a compound of any one of claims 1-15.

17. A field effect transistor comprising a semiconductor of claim 16.

18. A radio frequency identification device comprising a semiconductor of claim 16.

19. A photovoltaic device comprising a semiconductor of claim 16.