Pentacene soluble precursor

The first successful application of this method was reported by Mullen and coworkers [18]. The removal of their solubilizing group occurs thermally at temperatures as low as 180 °C, yielding pentacene and a volatile tetrahalobenzene. The tetrachloro compound 4 (Fig. 3.3) formed good-quality films from spin-cast solution, and heating the film of the soluble precursor at 200 °C for 5 s yielded the desired acene film. FET properties for devices made from solution-cast films were quite good - measured mobilities were as high as 0.2 cm2 V-1 s-1 with on/off current ratios of 106. 

The preparation of a soluble precursor of pentacene (3a) that can be spun-cast and then heated to form pentacene has been reported.[246-248] The pentacene precursor (Figure 3.1.15) is soluble in dichloromethane and forms a continuous, amorphous film when spun onto transistor substrates. A simple thermal treatment converts the precursor to pentacene via the elimination of tetrachlorobenzene. Thin films of pentacene formed by this technique demonstrated field-effect mobilities ranging from 0.1-0.2 cm V s for films converted at 200°C. 

An alternative route to solution-processible organic semiconductors is to use precursors to small molecule semiconductors, such as pentacene [59] or tetrabenzo-porphyrin [60], which can be converted into their fully conjugated, insoluble form by thermal or irradiative [61] treatment on the substrate. Pentacene precursors have been shown to yield field-effect mobilities of 0.01-0.1 cm2 V-1 s 1 [62], and 0.1-0.8 cm2 V-1 s 1 [63] after thermal conversion at 150-200 °C. Small molecule organic semiconductors can also be rendered solution processible by attachment of flexible side chains [64-66], Due to the relatively low solubility of these molecules the growth of uniform thin films of these molecules remains challenging, however. 

Herwig, P.T. and Mullen, K.A. (1999) A Soluble Pentacene Precursor Synthesis, Solid-State Conversion into Pentacene and Application in a Field-Effect Transistor. Adv. Mater., 11, 480-483. 

Recently a novel approach for a high yield synthesis of another soluble pentacene precursor was demonstrated.[249,250] The synthesis involves a Lewis acid-catalyzed Diels-Alder reaction of pentacene and N-sulflnylacetamide.[251-253] OTFTs fabricated by spin-casting a chloroform solution of the precursor on substrate followed... 

P.T. Herwig and Mullen, K., A soluble pentacene precursor synthesis, solid-state... 

The first example of a pentacene precursor was a tetrachlorocyclohexadiene adduct prepared by the Mullen group (Figure 5.3.9a) [47]. This derivative is soluble in dichloromethane and forms good films by spin-coating. After deposition, the pentacene film is formed by a thermally activated retro Diels-Alder reaction expelling tetrachlorobenzene as the by-product. The hole mobilities of OFETs prepared from these pentacene precursors depended greatly on the annealing temperature... 

Herwig, P.T. and Mullen, K., A soluble pentacene precursor Synthesis, solid-state conversion into pentacene and application in a field-effect transistor, Adv. Mater 11, 480-484, 1999. 

Joung, M.J. et ah. New soluble pentacene precursors for the application of organic thin-fikn transistors. Bull. Korean Chem. Soc. 24, 1862-1864, 2003. 

Another approach to patterning is to sensitize the target material to directly be photosensitive and wash off the remaining material. A number of custom compounded and commercially available materials have been applied as pho-topatternable gate dielectrics. A similar strategy has also been demonstrated for a soluble pentacene precursor, which converts to an insoluble and well ordered form after treatment [60], and conductor traces in an integrated circuit device [61]. 

Nontraditional HBC architectures have also gained synthetic interest recently. Contorted HBCs were expeditiously synthesized in three facile steps by Nuckolls and co-workers using a FeCU-mediated Scholl reaction. The Scholl reaction precursor 30 was obtained via a two-step synthesis from a soluble pentacene quinone derivative which could then undergo an intramolecular cyclization to afford the contorted HBC 31 in high yield. 

---