Spin-Coated Thin Films of Polycyclic Aromatic Hydrocarbons Exhibiting High SCLC Hole Mobilities

Abstract

High charge carrier mobilities have been greatly sought after in the development of cutting-edge organic electronic and optoelectronic devices. Although high field-effect transistor hole mobilities have been reported for solution-processed organic semiconductor thin films, their space-charge-limited current (SCLC) mobilities are still substantially lower. Herein, we report the synthesis and thin film SCLC hole mobilities of four polycyclic aromatic hydrocarbons, specifically, 2,5,8,17-tetra-tert-butyldiacenaphtho­[1,2-j:1′,2′-l]­fluoranthene (1), 2,5,8,11,14,17-hexa-tert-butyldiacenaphtho­[1,2-j:1′,2′-l]­fluoranthene (2), 2,9,12,15-tetra-tert-butylacenaphtho­[1,2-j]­benzo­[l]­fluoranthene (3), and 2,9,12,15-tetra-tert-butyl-4,5,6,7-tetraphenylacenaphtho­[1,2-j]­benzo­[l]­fluoranthene (4). Spin-coated pristine thin films of compounds 1–4 exhibit SCLC hole mobilities of 1.18 ± 0.18 × 10–3, 3.8 ± 0.9 × 10–5, 2.00 ± 0.87 × 10–3, and 2.27 ± 0.67 × 10–4 cm2 V–1 s–1, respectively. Upon thermal annealing at 120 °C for 10 min, compounds 1, 2, and 4 show limited changes in their optical properties and hole mobilities. In contrast, thermal annealing of thin films of 3 leads to broadened and red-shifted absorptions and emissions as well as drastically improved SCLC hole mobilities as high as 3.4 ± 0.1 × 10–1 cm2 V–1 s–1, one of the highest ever recorded SCLC hole mobilities on solution-processed organic semiconductor thin films. This improvement of the hole mobilities for the thin films of 3 is attributed to its radically enhanced crystallinity and intermolecular π–π overlap. Expansion of compound 3’s acene core with the hopes of further strengthening the π–π stacking interaction and thus further improving the SCLC mobility was unfortunately unsuccessful as the resulting molecule exhibits poor film formation properties.

Synthesis and Properties of a Decacyclene Monoimide and a Naphthalimide Derivative as Three‐Dimensional Acceptor–Donor–Acceptor Systems

“…The predictions are in good agreement with the absorption spectral differences displayed by 1 a and 2 a (Figure and Table ). As was mentioned in a previous publication, 5 b with a relatively high dipole moment (3.0 D) exhibits self‐aggregation behavior in CDCl 3 . According to crystallographic analysis of 5 b , the compound exists in a head‐to‐tail dimer form in the solid state.…”

“…Thus, the E LUMO of 2 c is lowered by the influence of the NI moiety (−2.81 eV), and its E HOMO is maintained at a relatively high energy (−5.65 eV). The LUMO energy of 2 c is comparable to that of perylene monoimide (−2.78 eV) . Thus, the energy gap between the E HOMO and E LUMO of 2 c (2.84 eV) is smaller than that of 1 c (2.97 eV).…”

“…Because the upfield shift in the aromatic protons (Ha shown in Figure b and S6) is a consequence of intermolecular ring‐current effects, it is possible that 2 a forms a head‐to‐tail dimer (Figure a). Previously, we showed that related substance 5 b formed an aggregate in CDCl 3 with a K a value of (39±4.9) m −1 , a rare occurrence for a monoimide derivative . Monoimide 2 a , possessing four bulky tert ‐butyl groups, has a K a value that is approximately four times larger than that of 5 b , and this is indicative of the existence of considerably stronger π–π attractive interactions between the DCMI molecules.…”

“…The high reversibility of the CV curve indicates that the radical anion and dianion of 2 a have high stabilities. Relative to the reduction potentials of AFI 5 b (−1.91 V in CH 2 Cl 2 containing 0.1 m Bu 4 NClO 4 ), those of 2 a indicate that it has high electron affinity as a consequence of the effects of the extended π conjugation. Analogous to 1 a , 2 a does not undergo observable oxidation <+1.3 V. On the other hand, a single reversible one‐electron oxidation wave, a single irreversible one‐electron reduction wave, and a single seemingly reversible two‐electron reduction wave are seen in the CV curve of 8 a at +1.10, −1.33, and −1.60 V, respectively (Figure b).…”

“…As part of an investigation exploring the electronic and supramolecular properties of N‐n ‐octylacenaphtho[1,2‐ j ]fluoranthene‐4,5‐dicarboxylic imide (AFI, 5 b ), we prepared 5 b and showed that it has novel electronic and supramolecular properties . Shortly thereafter, Kilway and Peng's group reported the synthesis of tetra‐ tert ‐butyldecacyclene by using the DA reaction of 2,5,9,12‐tetra‐ tert ‐butyldiacenaphtheno[1,2‐ b ;1′,2′‐ d ]thiophene ( 3 b ) with acenaphthylene . This observation, which stands as the sole example of the preparation of a DC derivative having C 2 v symmetry, suggest that thiophene derivatives 3 a and 3 b should be versatile building blocks for the construction of polycyclic conjugated systems having potentially interesting electronic and optical properties …”