Organic semiconductors have attracted attention in the art due to their potential applications in making large area, flexible, and low-cost electronic devices, including organic light-emitting diodes (OLEDs), solar cells and/or transistors. Such organic semiconductors can be relatively low molecular weight “small molecules” that can be vapor deposited. Alternatively, semiconducting organic oligomers or polymers can be solution processed to form organic semiconductor films at the low costs necessary to enable many new and desirable end use applications. See for example a review article by Shirota and Kageyama (Chem. Rev. 2007, 107, 953-1010).
While quite a number of organic semiconductor small molecules, oligomers, and/or polymers have been reported in the prior art that can transport holes reasonably efficiently, the identification, synthesis, and uses of organic semiconductor compounds that can efficiently transport electrons, especially in the presence of air and/or water, has proven much more difficult, especially if solution processability is also desired.
Among the best examples of electron transporting compounds from the prior art that are vapor processable are monomeric “small molecule” naphthalenediimide (“NDI”) and perylenediimide (“PDI”) compounds having the structures shown below;
 R1R2R1R21aC8H17H1bC8H17H2aCH2C7F15H2bCH2C3F7H3aC8H17CN3bC6H12CN4CH2C4F7CN
It is known that measured “field-effect” electron mobility values, current on/off ratios, and threshold voltages measured from organic field effect transistors “OFETs” cannot be considered representative of the intrinsic mobility values of a given material, but rather are a measure of their ability to function in a given device configuration that can vary very significantly with the selection of electrode, dielectric, the channel width, the channel length, the mode of deposition, the processes of post-deposition treatment such as but not limited to thermal annealing, and other transistor device structure details used in such OFET devices, as well as the specific compatibility and suitability of the selection of the other components of such OFETs with the physical and electronic properties of each organic semiconductor. Nevertheless, Table 1 below summarizes the best prior art results known to Applicants for vapor deposited “small molecule” OFETs in specific device configurations.
TABLE 1OFET device data for select rylene diimidesmall molecules (vacuum deposited).Field EffectMobility μeVTOperation(cm2V−1s−1)ION/IOFF(V)Device structure1aVac.0.16TC gold on Si/SiO2Air10−61bH21.710710-15BC Ag on Si/SiO2coated withpoly(α-methylstyrene)1bAir0.1110511TC gold on Si/SiO2coated with PMMA;2aAir0.1105TC gold on Si/SiO22bAir0.5110628-43TC gold on Si/SiO2treated with OTS3aAir0.11103−55TC gold on Si/SiO23bAir0.1010515TC gold on Si/SiO2treated with HMDS4Air0.64104−20TC gold on Si/SiO2treated with HMDSVT = threshold voltage; TC = top contact; BC = bottom contact; OTS = octadecyltrichlorosilane; HMDS = hexamethyldisilazane; PMMA = poly(methyl methacrylate); Vac. = vacuum.
NDI compound 1a was reported (see Katz, H.; Johnson, J.; Lovinger, A.; Li, W. Journal of the American Chemical Society 2000, 122, 7787) to exhibit a measured field-effect electron mobility of 0.16 cm2 V−1 s−1 in vacuum, but almost no field-effect electron mobility was measurcable in air. PDI compound 1b was reported to achieve a maximum field-effect mobility of 1.7 cm2 V−1 s−1 in an H2 atmosphere, but, the field-effect mobility was dramatically reduced to 0.11 cm2 V−1 s−1 when the device was exposed to air (Chesterfield, R.; McKeen, J.; Newman, C.; Ewbank, P.; da Silva, D.; Bredas, J.; Miller, L.; Mann, K.; Frisbie, C. Journal of Physical Chemistry B 2004, 108, 19281). PDI compound 4 was reported to have an air-stable field-effect electron mobility of 0.64 cm2 V−1 s−1 (see Jones, B.; Ahrens, M.; Yoon, M.; Facchetti, A.; Marks, T.; Wasielewski, M. Angew Chem Int Ed 2004, 43, 6363), but only produced an on/of ratio of 1×104 in the reported OFET, and suffered from an undesirable threshold voltage of −20 volts.
It is believed in the art that the mobility of electrons through materials comprising such NDI and/or PDI compounds results from a combination of the electronic properties of the highly conjugated compounds, as well as (at least in some favorable cases) face-to-face π-stacking interactions between neighboring NDI or PDI small molecules in the solid state.
Yan and Zhao (Org. Lett. 2009, 11(15) 3426-3419) reported the synthesis and characterization of several solution processable bis(PDI) oligomeric compounds bridged by phenyl or acetylene groups, as shown below:

Yan and Zhao noted that in some such PDI oligomers (connected at the bay positions) reported in the prior art, some bridging groups appeared to induce an electronic effect on the LUMOs of the PDI groups. With respect to the PDI-X-PDI oligomers they described, Yan and Zhao concluded that an acetylene bridge permitted electronic conjugation between the two perylenediimide groups, but that phenyl bridges did not permit such electronic conjugation, probably because of steric interactions between the PDI and phenyl groups that induced highly twisted/non-coplanar conformations of the PDI and bridging groups. Yan and Zhao did not report measurements of the electrical conductivity properties of the PDI-X-PDI oligomers they described as electron carrier semiconductors.
Recently in 2009, PCT Patent Publications WO 2009/144205 and WO 2009/144302 described a very wide genus of bridged bis(rylene) compounds having the formula Q-L-Q′, wherein Q and Q′ could be a wide variety of rylene groups that included NDI, PDI and many other groups. L was also described as including a very wide variety of cyclic and non-cyclic bridging groups. From the extremely broad genus of Q-L-Q′ compounds broadly disclosed in the publications, both WO 2009/144205 and WO 2009/144302 more specifically described the specific solution processable PDI-bis-thiophene-PDI compound whose structure is shown below (where Rb is 2-ethyl-hexyl), and reported that bottom-gate, top contact field effect transistors employing that compound (and tested in air) gave measured field effect mobility values as high as 0.05 cm2V−1sec−1, on/off ratios of 2.4×106, but suffered from undesirable threshold voltages of −15 volts. It was not clear whether or not the reported transistors were stable in air past the short time required for the electronic measurements.

However, in order to provide practically useable transistor device performance, and employ solution processing so as to reduce manufacturing costs so as to enable practical new commercial applications in organic electronic devices such as OFETs, solution processable and long-term air-stable electron transport materials having much better performance, such as low barriers for charge injection, high field-effect mobility of charge carriers (>1 cm2V−1s−1), large ION/IOFF ratios (>106), and low threshold voltage (<±2.5 V) are still needed.
Accordingly, there remains a need in the art for improved solution processable organic semiconducting materials that can transport holes, and/or electrons in transistor applications in air, with high carrier mobility, high current on/off ratios, and/or threshold voltages close to zero. It is to that end that the various embodiments of the inventions described herein relate.
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