Pentacene precursor

Afzali, A. Dimitrakopoulos, C. D. Breen,T. L. 2002. High-performance, solution processed organic thin film transistors from a novel pentacene precursor. J. Amer. Chem. Soc. 124 8812-8813. 

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. 

Afzali, A., Dimitrakopoulos, C.D. and Graham, T.O., Photosensitive pentacene precursor Synthesis, photothermal patterning, and apphcation in thin-fihn transistors, Adv. Mater, 15, 2066, 2003. 

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. 

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... 

However, a major problem with the pentacene precursor method is that a residual amount of the Diels-Alder adduct remains in the film and limits the carrier mobility of the final pentacene film [54]. To limit this problem, pentacene precursors with smaller or more easily eliminated Diels-Alder adducts have recently appeared, but the field-effect transistor characteristics of these new derivatives are yet to be published (Figure 5.3.9c) [55,56]. 

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]. 

A. Afzali, C. D. Dimitrakopoulos, and T. L. Breen. High-Performance, Solution-Processed Organic Thin Film Transistors from a Novel Pentacene Precursor. Journal of the American Chemical Society, 124(30) 8812-8813, 2002. 

K. R Weidkamp, A. Afzali, R. M. Tromp, and R. J. Hamers. A Photopattern-able Pentacene Precursor for Use in Organic Thin-Film Transistors. Journal of the American Chemical Society, 126(40) 12740-12741, 2004. 

FIGURE 15.5 OFET mobility based on the solution-based fabrication using pentacene precursors. 

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