Substituted Cyclopentannulated Tetraazapentacenes

Abstract

Brominated pentannulated dihydrotetraazapentacenes were prepared by gold- or palladium-catalyzed 5-endo-dig cyclization of TIPS-ethynylated dihydrotetraazaacenes (TIPS = triisopropylsilyl). Post-functionalization was demonstrated by Sonogashira alkynylation and Rosenmund-von Braun cyanation. Calculations predict these species to act as n-type semiconductors, which was verified for two derivates through characterization in organic field-effect transistors.

Keywords: cyclization; dihydroazaacenes; postfunctionalization; semiconductors; solid-state packing.

Scheme 1

Top: Examples of the stabilization of (aza‐)acenes by annulation. Bottom: Synthesis of non‐halogenated cyclopentannulated dihydrotetraazapentacenes. Conditions: i) IPrAuNTf₂ (10 mol%), DCE, 80 °C, 16 h; ii) PdCl₂ (10 mol%), MeCN/CHCl₃ 1 : 1, 80 °C, 18 h.

Scheme 2

Synthesis of brominated cyclopentannulated tetraazapentacenes 3 a–d and 4 a–c. Conditions: i) IPrAuNTf₂ (10 mol%), DCE, 80 °C, 2 d; ii) PdCl₂ (10 mol%), MeCN/CHCl₃ (1 : 1), 80 °C, 18 h. Yields in red: gold catalysis; yields in black: palladium catalysis.

Scheme 3

Post‐functionalization of 4 c by cyanation or alkynylation.

Figure 1

Top: Photographs of D, 3 d, 4 c, 5 c and 6 c in DCM under irradiation by UV light (365 nm). Middle: Normalized emission spectra of D, 3 d, 4 c and 5 c in DCM (solid line) and of 5 c as powder (dashed line). Bottom: Normalized absorption spectra of D, 3 d, 4 c and 5 c in DCM.

Figure 2

Single crystal structures of a) 3 a, b) 3 b, c) 3 c, d) 3 d, e) 4 b, f) 5 c and crystal structure packing of g) 3 d and h) 5 c. For the single molecules, hydrogen atoms were omitted for clarity. For crystal packing TIPS‐groups and co‐crystallized solvents were also omitted.

Figure 3

a) Transfer characteristics of 3 d. b) Micrograph of a film of 3 d. c) Transfer characteristics of 5 c. d) Micrograph of a film of 5 c. e) Charge transfer mobilities (electron) of 3 d and 5 c.

Figure 4

Time‐dependent decrease in the absorption bands of TIPS‐TAP (679 nm), D (468 nm), 3 d (478 nm), 4 c (486 nm) and 5 c (499 nm) under irradiation with white and UV light (365 nm) in DCM under air. For clarity, intensity values were fitted with an exponential fit (except for 5 c).