Synthesis and characterization of S,N-heterotetracenes

The synthesis and optoelectronic properties of novel S,N-heterotetracenes consisting of fused heterocyclic thiophene and pyrrole rings are presented. Tetracyclic and benzannulated derivatives with a varying number and sequence of sulfur and nitrogen heteroatoms were synthesized in multistep synthetic routes. A Buchwald–Hartwig amination of brominated precursors, thermolysis of azide precursors, and a Cadogan reaction of nitro-substituted precursors were successfully applied to eventually build-up pyrrole rings to stable and soluble fused systems. The various obtained heteroatom sequences ‘SSNS’ (SN4), ‘SNNS’ (SN4’’), and ‘NSSN’ (SN4’) allowed for evaluation of structure–property relationships relative to the sulfur analogue tetrathienoacene (‘SSSS’). In line with the results for the whole series of S,N-heteroacenes, we find that replacement of sulfur by nitrogen atoms in the tetra- and hexacyclic systems leads to a red-shift in absorption, a decrease in oxidation potential and energy gap. On the other hand, the replacement of a thiophene ring by benzene leads to the opposite effects.

Instruments and measurements. NMR spectra were recorded on a Bruker AMX 500 ( 13  Single crystals of thienopyrrole 25 were analysed on a Bruker SMART APEX-II CCD diffracttometer ((MoK)-radiation, graphite monochromator,  and 4 scan mode) and corrected for absorption using the SADABS program [1]. The structures were solved by direct methods and refined by a full-matrix least squares technique on F 2 with anisotropic displacement parameters for non-hydrogen atoms. The hydrogen atoms were placed in calculated positions and refined within the riding model with fixed isotropic displacement parameters (UISO(H) ¼ 1.2Ueq(C)). All calculations were carried out using the SHELXL program package in Olex2 (v.  [5], tosylazide [6], and 2-bromo-3-nitrothiophene 15 [7] were internally synthesized according to literature-known procedures.
Thieno [3,2- mmol) was added dropwise and the solution was stirred for 3 h at this temperature. The solution was allowed to slowly warm to room temperature overnight. n-Hexane (50 mL) and brine (50 mL) were added. The organic phase was collected and dried over MgSO4. After removing the solvent in vacuum, the residue was further purified by column chromatography  (4). Synthesis was analogous as described in [9]. To a solution of diisopropylamine (0.64 mL, 4.55 mmol) in dry THF (55 mL) at 0 °C was added n-BuLi (1.6 M in n-hexane, 2.40 mL, 3.84 mmol) under Ar atmosphere. After Analytical data is in accordance with literature data [9].
The analytical data is in accordance with the product obtained via the azide route (vide supra).   [12].
Subsequently, n-BuLi (7.78 mL, 12.5 mmol, 1.6 M in n-hexane) was slowly dropped in and the reaction mixture was stirred for additional 15 min at -78 °C. Then, it was warmed to rt and stirred for one hour at this temperature. The reaction mixture was cooled to -78 °C and triisopropylsilyl chloride (2.64 mL, 12.5 mmol) was dropped in and slowly warmed to rt over 14 h.
Water was added and the solution extracted twice with diethyl ether (100 mL each) and twice with dichloromethane (100 mL each). The combined organic phases were dried over sodium sulfate, the solvent stripped off and the product was isolated by column chromatography        Table S1: X-ray structure analysis data of thienopyrrole 25.