Two 1,4,8,11-tetraalkyl-6,13-diphenylpentacenes were prepared. X-ray analysis revealed that the methyl derivative had a herringbone arrangement with ³-overlap, while the propyl derivative had a slipped-parallel structure without ³-overlap. The solid-state order reflected UVvis absorption spectra in the solid state.Pentacene has attracted much attention as a p-type organic semiconductor, because of the high field-effect transistor (FET) mobilities of its crystals and thin films.1 However, pentacene is insoluble in common organic solvents, and the development of solution-processing electronic devices is desired. Therefore, a number of soluble pentacene derivatives with substituents have been prepared.2,3 For instance, Anthony et al. prepared a variety of 6,13-disubstituted pentacenes, whose substituents contained functionalized ethyne units. Interestingly, the substituents controlled the solid-state order that is a significant factor in the performance of FET devices.3 Nuckolls et al. reported an X-ray crystal structure and a poor hole mobility (8 © 10 ¹5 cm 2 V ¹1 s ¹1 ) of 6,13-diphenylpentacene, 2g which had first been prepared in 1942. 4 We were impressed particularly by the unique crystal structure, which displayed that the pentacene cores in a column direction were arranged cofacially, although the long molecular axes of nearest neighboring acenes were orthogonal. Additionally, the intermolecular distance between pentacene planes was ca. 5.0 ¡.2g As a result, there was no ³-overlap between pentacene frameworks, but only edge-to-face interactions between phenyl and pentacene rings.Since it is recognized that the solid-state order can significantly affect charge transport properties as well as intermolecular interactions, the control of stacking arrays of acene moieties is a critical issue for electronic devices. Recently, we prepared a series of alkyl-substituted tetracenes on the terminal benzene rings. 5 We found that the alkyl side chains had abilities to tune both molecular arrangements and photophysical properties in the solid state. To metamorphose the unique stacking pattern of 6,13-diphenylpentacene mentioned above, we introduced alkyl side chains onto the terminal A and E rings in pentacene (Figure 1). We report here the synthesis and crystal structures of 6,13-diphenylpentacene derivatives 1a and 1b having methyl and propyl groups, respectively, at the 1-, 4-, 8-, and 11-positions.1a and 1b were prepared as shown in Scheme 1.6 First, we thought that the synthesis could be achieved via a reaction of PhLi and 1,4,8,11-tetraalkyl-6,13-pentacenequinones, which was prepared using a method proposed by Hanack et al. 7 Since the key intermediates were 3,6-dialkyl-1,2-bis(bromomethyl)-benzenes 7a and 7b, we prepared the o-xylene-¡,¡¤-diols 4a and 4b as precursors. The methyl derivative 4a was prepared from a DielsAlder reactiondehydration sequence between 2,5-dimethylfuran (2) and maleic anhydride according to a literature procedure.8 Although the propyl derivative 4b could be obtained using the same proced...
