Regioisomeric Control of Charge Transport Properties in Fluoranthene-Fused 12-Ring Heteroarenes

Abstract

Heteroarene-based organic semiconductors (OSCs) have emerged as promising material candidates for large-area, flexible electronic and photonic devices due to their favorable π-conjugation systems and tunable optoelectronic properties. However, their development is still hindered by synthetic and design challenges, in particular, the limited access to highly polycyclic heteroarenes with tunable properties and the unexplored effects of topological isomerism. Here, we have successfully synthesized three regioisomeric thienoacenes (BTFA4-6) by fusing a dicyanofluoranthene unit, which have an identical 12-fused ring composition but different molecular topologies with [a] or [c]-fusion and syn or anti-CN substitution. We demonstrate that solution-processable BTFA4-6 exhibits topology-dependent charge transport properties by fabricating organic field-effect transistors. BTFA4 with [a]-fusion and syn-CN substitution and BTFA6 with [c]-fusion and syn-CN substitution show only typical n-type semiconducting behavior, with electron mobilities of 3.91 × 10^-4 and 1.58 × 10^-5 cm² V^-1 s^-1, respectively, while BTFA5 with [a]-fusion and anti-CN substitution achieves electron-dominated ambipolar behavior, with an increase in electron mobility (3.45 × 10^-2 cm² V^-1 s^-1) by 2 orders of magnitude and a hole mobility of 4.31 × 10^-3 cm² V^-1 s^-1. Therefore, this work establishes that regioisomeric molecular engineering is a powerful tool for manipulating the charge transport properties of heteroarene-based OSCs.

Keywords: Charge transport property; Heteroarene; Organic semiconductor; Regioisomerism.

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(a) The molecular structures of representative heteroarenes analogues; ,− (b) schematic diagram of the design of 12-ring-fused heteroarenes based on 2,3-dicyanofluoranthene; (c) the molecular structures of BTFA4–6 studied in this work.

1. Synthetic Routes of BTFA4-6

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(a) ¹H NMR spectra of BTFA4–6 in CDCl₃, (b) DFT-optimized geometry (side-view), (c) electrostatic potential distribution, and (d) NICS(0) (top)/NICS(1)_ZZ (bottom, parenthesized) values of BTFA4–6.

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Absorption spectra of BTFA4–6 (a) in CH₂Cl₂ solutions and (b) in films. (c) TGA curves of BTFA4–6 measured in N₂ at a heating rate of 10 °C/min. DSC curves of (d) BTFA4, (e) BTFA5, and (f) BTFA6 measured in N₂ at a heating rate of 10 °C/min.

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(a) AFM height images, (b) phase images, (c) optical images, and (d) 2D-GIWAXS patterns of the films of BTFA4–6.

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n-Type transfer characteristics of the OFET devices based on (a) BTFA4 and (b) BTFA6. (c) Ambipolar transfer characteristics of the OFET device based on the BTFA5.