Pentacene‐Based Polycyclic Aromatic Hydrocarbon Dyads with Cofacial Solid‐State π‐Stacking

Abstract

Give me five! Pentacene‐based polycyclic aromatic hydrocarbon (PAH) dyads are synthesized via an unsymmetrical pentacene building block. These molecules exhibit cofacial solid‐state π‐stacking as a result of the large aromatic chromophores. The choice of the PAH attached to the pentacene (see picture) influences the electronic properties as determined by UV/Vis absorption/emission spectroscopy and cyclic voltammetry.

Aryl substitution of pentacenes

“…Substituted pentacenes 3a–k are slightly easier to oxidize than TIPSPc ( E ox1 = 0.39 V), and the E ox1 values of 3a – k fall into a similar range as found for pentacene-based PAH dyads 2a – c in which the pendant aryl groups are linked by an ethynyl spacer that allows electronic communication between the two arenes [18]. The range of oxidation potentials between TIPSPc, 2a – c , and 3a – k is, however, quite narrow, suggesting that the pendent substituent offers little influence on the HOMO level.…”

“…TGA shows clearly that significant mass loss occurs in the range of 400 °C, which is also common for ethynylated pentacenes such as 1 and 2 [17–18]. There appears to be little evidence of a trend based on the size of the aryl group versus the temperature of observed mass loss in the TGA.…”

“…After reaction with the appropriate aryl lithium species, the reaction was quenched with a proton source, and the resulting diol intermediates 5a–h were carried on directly to reductive aromatization with SnCl 2 /H 2 SO 4 without further purification, ultimately yielding pentacene products 3a – h . While the isolation and characterization of diol products resulting from nucleophilic additions to pentacenequinone has been possible [17–18 34], previous work has shown that aromatized products were more easily purified by column chromatography and recrystallization following the last step [30–31 36]. Thus, it was deemed procedurally more efficient to eliminate the purification step of the intermediate diols.…”

“…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.…”

Sonogashira reactions for the synthesis of polarized pentacene derivatives

“…These polycyclic aromatic hydrocarbons were attached to the pentacene through an ethynyl linker to provide extended conjugation. 11 Pentacene derivatives have also found potential applications in photoredox catalysis as pure organic photocatalysts that can be an alternative to expensive iridium complexes.…”