Dibenzannulated peri-acenoacenes from anthanthrene derivatives

Abstract

A series of dibenzannulated phenyl-annulated [4,2]peri-acenoacenes have been synthesized in three straightforward steps from 4,10-dibromoanthanthrone (vat orange 3). The phenyl bisannulation of [4,2]peri-acenoacene provides extra stability by increasing the overall aromatic character of the molecules, and allows for a 45-80% increase of the molar extinction coefficient (ε) compared to their [5,2]peri-acenoacene isomers. Depending on the substituents attached to the π-conjugated core, some derivatives exhibit strong aggregation in the solid state with association constant (K_a) up to 255 M^-1, resulting in a significant broadening of the absorption spectrum and a substantial decrease of the bandgap value (more than 0.3 V) from solution to the solid state. One [4,2]peri-acenoacene derivative was doubly reduced using cesium and the crystal structure of the resulting salt has been obtained. Field-effect transistors showing a temperature-dependent hole mobility have been tested.

Fig. 1. Examples of zigzag-edged polycyclic aromatic hydrocarbons.

Scheme 1. Synthesis of dibenzannulated phenyl-annulated [4,2]peri-acenoacenes 2a–d.

Fig. 2. Absorption (CHCl₃, solid lines) and fluorescence spectra (CHCl₃, dashed lines) of compounds 2a–d.

Fig. 3. Absorption spectra in solution (CHCl₃, solid line) and in solid state (dashed lines) of compound 2c.

Fig. 4. ¹H NMR of compound 2a between 7.5 ppm and 11.0 ppm at different concentrations [0.3–18.3 mM] in CDCl₃ at room temperature.

Fig. 5. (a) Kohn–Sham molecular orbitals of model compounds of 2a–d based on calculations at the B3LYP/6-31G(d,p) level of theory. (b) NICS(0) values (in ppm) for the different rings in dibenzannulated phenyl-annulated [4,2]peri-acenoacene 2a and 2a²⁻. The values have been calculated for compound 2a. The TIPS-acetylene groups have been omitted for clarity.

Fig. 6. Crystal structure of [{Cs⁺(18-crown-6)₂}₂(2a²⁻)] in ball-and-stick model, H-atoms are omitted for clarity.

Fig. 7. Solid-state packing of [{Cs⁺(18-crown-6)₂}₂(2a²⁻)] in ball-and-stick (no H-atoms, left) and space-filling (right) models. The {Cs⁺(18-crown-6)₂} moieties are shown in green.

Fig. 8. Charge transport measurements of compound 2a conducted in a vacuum at room temperature. (a) The output curve displays close to ideal p-type transport. (b) Linear-regime transfer curve and (c) the corresponding charge carrier mobility.