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. 2024 Mar 6;146(9):5793-5798.
doi: 10.1021/jacs.3c13629. Epub 2024 Feb 27.

Stabilizing Azaheptacenes

Wansheng Zong  1 , Nikolai Hippchen  1 , Nico Zeitter  1 , Steffen Maier  1 , Philipp Ludwig  1 , Frank Rominger  1 , Jan Freudenberg  1 , Uwe H F Bunz  1
Affiliations

Stabilizing Azaheptacenes

Wansheng Zong et al. J Am Chem Soc. .

Abstract

The symmetrical 7,16-diaza-6,8,15,17-tetrakis(triisopropylsilylethynyl)heptacene was obtained by a Pd-catalyzed reaction of a 2,3-diamino-1,4-diethynylanthracene with a 2,3-dibromo-1,4-diethynyl anthracene. Positioning the TIPS-ethynyl groups adjacent to the central ring suppresses dimerization via [4+4] cycloadditions and Diels-Alder reactions; the middle pyrazine ring renders this species stable to oxidation. A single crystal structure was obtained, and thin film transistors with μn = 0.042 cm2 V-1 s-1 were produced. Transposition of the alkynyl groups into the 5,8,15,18-positions with a quinoxaline unit in the center of the heptacene decreases the stability, as does the introduction of two more nitrogen atoms into the 5,18-positions. The hydrocarbon 6,8,15,17-tetrakis(triisopropylsilylethynyl)heptacene is reasonably stable with a half-life of 25 h in solution. Four correctly placed TIPS-ethynyl groups protect heptacene cores.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Known heptacene 1, diazaheptacene DAH3, and the (aza)heptacenes reported herein.
Scheme 1
Scheme 1. Synthesis of (Aza)heptacenes
Figure 2
Figure 2
(a) Normalized UV–vis absorption spectra of (aza)heptacenes in DCM (10–5 mol L–1). (b) Time-dependent evolution of UV–vis spectra of DAH1 (10–5 mol L–1 in dry DCM) under ambient light and atmosphere. Inset: magnification of the p-bands. (c) Evolution of UV–vis absorption intensities at λabs,max for (aza)heptacenes under ambient conditions (UV–vis spectra: see SI, Figure S13).
Figure 3
Figure 3
Solid state structures (representative depictions) and packing motif obtained for (aza)heptacenes; hydrogen atoms are omitted for clarity. Note that for TAH, the position of the noncentral pyrazine is statistically disordered due to the centrosymmetry of the lattice. π-Stacking distances are estimated from the mean distances of the (aza)acene backbones. Corresponding atomic colors: carbon, gray; nitrogen, blue; silicon, yellow; chlorine, green.
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