Study on liquid crystallinity in 2,9‐dialkylpentacenes

Abstract

A series of semiconducting and symmetrical 2,9-dialkylpentacenes was successfully synthesized via a five-step process and their structures confirmed by 1 H NMR, IR and elemental analyses. Their liquid crystallinity was investigated by differential scanning calorimetry and polarizing optical microscopy. The introduction of alkyl chains also improved their solubility. For alkyl chains longer than butyl, focal conic or baton texture was observed, indicating the existence of an ordered smectic phase. Thermal analyses revealed that the both melting and smectic-isotropic transition temperatures show an odd-even effect when the alkyl chain is larger than heptyl or octyl. The synthesized compounds are promising candidates for semiconductors in organic field-effect transistors because their liquid crystallinity allows easy molecular alignment in the device fabrication process.

Synthesis, 2D NMR and X-ray diffraction studies on Cu(II) and Ni(II) complexes with ligands derived from azobenzene-cored Schiff base: Mesomorphic behaviors of Cu(II)–phenolates and crystal structure of bis[4-(4-alkoxy-2-hydroxybenzylideneamino)azobenzene]copper(II)

“…However, the odd-even effect becomes less distinctive when the number of carbon in the alkoxyl chain, n is larger than 8. This is due to the increase in flexibility of the terminal alkoxyl chain [36][37][38]. These observations strongly show that ligands with even number of terminal alkoxy chain have higher clearing point than those with odd numbers.…”

Organic Semiconductors and Conductors with tert-Butyl Substituents

“…Acylation of tert-butylbenzene with pyromellitic dianhydride afforded di(p-benzoyl)benzene (9) [16,17], which was cyclized by sulfuric acid to give tert-butyl substituted pentacene diquinone (10). Compound (2) was, however, not obtained by the reduction of (10) with sodium borohydride or lithium aluminium hydride, though there were reports on the reduction of (10) with aluminum amalgam [18] and the reduction of (9) with palladium carbon under H 2 atmosphere [11]. Scheme 2.…”

“…Prompted by these findings, we have synthesized tert-butyl substituted TTF (1); pentacene (2); and quarterthiophene (4T, 3) molecules (Figure 1), and investigated the structural and transistor properties. The former two are new compounds, though several alkyl-substituted TTF and pentacene molecules have been reported [9][10][11][12]. Although alkyl-substituted oligothiophenes have been extensively studied [13], the tert-butyl substituted 4T has been studied to some extent only in the S-dioxide form [14].…”

Alkylated oxygen-bridged V-shaped molecules: impacts of the substitution position and length of the alkyl chains on the crystal structures and fundamental properties in aggregated forms

“…The first phase-transition temperatures (128-150°C) of C n -DNF-VWs observed during the heating process are still higher than those of the pentacene derivatives, as summarized in Supplementary Table 3. 2,9-Dialkylated pentacenes (n = 6, 8 and 10) transform into the smectic phase in the temperature range of 89-105°C, 6 at which the rod-type pentacene core are rotating along its molecular longitudinal axis in a lamellar mesophase. We thus conjectured that the bent-type DNF-V core could suppress the molecular spin motion, resulting in the higher phase-transition temperature.…”

“…Historically, pentacene has been regarded as a benchmark of highperformance organic semiconductors, 4 and its derivatives have been extensively developed. 5,6 The fatal drawbacks of pentacene (that is, its chemical instability and low solubility) were overcome by structural modification; for example, introduction of triisopropylsilylethynyl groups at 6,13-positions. 5,7 While triisopropylsilylethynyl pentacene shows chemical stability and improved solubility together with high carrier mobility in solution-processed film 8,9 exceeding that of amorphous silicon (0.5-1.0 cm 2 V − 1 s − 1 ), it transforms into the liquid crystal phase at 124°C.…”