Combining Electronic and Steric Effects for Highly Stable Unsymmetric Pentacenes

Abstract

This paper describes the reactivity of unsymmetrically substituted pentacenes to photochemical oxidation. Acenes in general, and pentacenes in particular, are a key family of compounds for a variety of organic electronics applications. The instability of many pentacene derivatives, particularly to oxidation, is an important restriction in their applicability. Several substitution strategies for decreasing the reactivity of pentacene exist, but these almost always involve symmetrically substituted derivatives, restricting the chemical space of structures from which to choose. In this paper, we demonstrate that combining electronic and steric effects yields highly stable unsymmetrically substituted pentacenes.

Aryl substitution of pentacenes

“…The most reactive positions of the acene core are the 6- and 13-positions [27–29], and these positions can be effectively blocked by different trialkylsilylethynyl units [30]. Inspired by previous studies in which we [18,31], and others [32–34], observed promising solid-state arrangement and properties of aryl-substituted pentacenes, we were interested in the influence of different aryl moieties directly linked to the pentacene core. In this work we present a simple synthetic approach to unsymmetrically substituted pentacenes via stepwise functionalization of pentacenequinone, using a nucleophilic aryl group (Fig.…”

Steric and Electronic Substituent Effects Influencing Regioselectivity of Tetracene Endoperoxidation

“…Consistent with reported observations of acene derivatives, substitution of one phenylethynyl substituent for an aryl substituent (comparing 1 to 3) results in a decrease in reaction rate with 1 O 2 . 13,14,22 Moreover, further substitution with ethyl groups in the ortho positions of aryl groups directly bound to the acene core also slows oxidation, with one ethyl group on an aryl substituent decreasing the rate of oxidation by one-third (comparing 3 to 4), and two ethyl groups (comparing 3 and 5) decreasing the rate of oxidation by two-thirds. We attribute this pattern to each ethyl group hindering one face of the acene.…”

“…The Journal of Organic Chemistry Note (m, 5H), 7.42−7.40 (m, 1H), 7.30−7.27 (m, 1H), 7.19 (d, J = 7.5 Hz, 1H) 13. C NMR (125 MHz, CDCl 3 ): δ 139.2, 138.3, 136.2, 135.3, 132.8, 132.6, 132.5, 129.8, 128.6, 128.5, 128.4, 128.3, 128.18, 128.16, 127.5, 127.0, 126.7, 123.5, 122.9, 121.9, 121.5, 95.0, 83.9, 79.0.…”

“…13−21 Rooted in our interest in understanding the effects of substituents on acene reactivity with 1 O 2 , 22 our group recently reported that highly persistent pentacene derivatives are available by combining on the central 6-and 13-positions (i) the steric effects from ortho-alkyl groups on an aryl ring substituent and (ii) the electronic effects of an ethynyl substituent, resulting from destabilization of radical or ionic intermediates of cycloaddition. 13 In contrast to the pentacene core, for which the central 6,13-site is the most reactive based on both frontier molecular orbital (FMO) and aromaticity analyses, the unsubstituted tetracene core has two central rings with equal reactivity. Therefore, the influence of differential substitution of these two sites on the regioselectivity of 1 O 2 addition can give important information regarding the localized substituent effects on reactivity.…”

“…1 14 (s, 1H). 13 Tetracene 3. 12-Hydroxy-12-phenylethynyltetracen-5-one (0.10 g, 0.28 mmol) was dissolved in 6 mL of dry THF and cooled to −78°C.…”