Azaacene Dimers: Acceptor Materials with a Twist

Abstract The synthesis of five spiro‐linked azaacene dimers is reported and their properties are compared to that of their monomers. Dimerization quenches emission of the longer (≥(hetero)tetracenes) derivatives and furnishes amorphous thin‐films, the absorption is not affected. The larger derivatives were tested as acceptors in bulk‐heterojunction photovoltaic devices with a maximum power conversion efficiency of up to 1.6 %.


Mass spectrometry
The mass spectra were recorded using the following instruments: Bruker ApexQe hybrid 9.4 T FT-ICR (MALDI); Bruker AutoFlex Speed time-of-flight (MALDI).

Melting points
Melting points were determined in open glass capillaries with a Melting Point Apparatus MEL-TEMP (Electrothermal, Rochford, UK).

Cyclic voltammetry
The cyclic voltammetry (CV) experiments were carried out using PGSTAT101 Potentiostat Galvanostat with a platinum working electrode (Metrohm 6.120.4190, diameter 1 mm), a platinum wire auxiliary electrode (Metrohm 3.109.0790), a silver wire reference electrode (Metrohm 6.1241.060), a 0.1 mol L -1 NBu4PF6 solution in degassed, dry DCM, and ferrocene/ferrocenium as the reference redox system and internal standard (−5.1 eV) at room temperature and 0.2 V s -1 . To determine the reduction and oxidation potentials, the half-wave potentials were used. [2] X-ray single-crystal structure analysis X-ray single-crystal structure analyses were measured on a Bruker Smart APEX-II Quazar Area Detector diffractometer by Dr. F. Rominger (Heidelberg University). Diffraction intensities were corrected for Lorentz and polarization effects. An empirical absorption correction was applied using SADABS based on the Laue symmetry of reciprocal space. Heavy atom diffractions were solved by direct methods and refined against F2 with the full matrix least square algorithm. Hydrogen atoms were either isotropically refined or calculated. The structures were solved and refined using the SHELXTL software package.

UV-Vis and fluorescence spectroscopy
Absorption spectra were recorded on a Jasco UV-Vis V-660 or Jasco UV-Vis V-670.
Fluorescence spectra were recorded on a Jasco FP-6500.

Quantum yields
Quantum yields were determined by an Ulbricht sphere (6 inch) using a PTI QuantaMaster 40 equipped with a Hamamatsu R928P Photomultiplier.

Camera
The photos were taken by a Canon EOS 7D under daylight or UV-light irradiation (λ = 365 nm).

General procedure:
In a heatgun dried Schlenk tube under an atmosphere of argon was added quinone 1 (1.00 equiv.) and the ortho-diamine 2 (2.00 equiv). Then chloroform and acetic acid were added and the reaction mixture stirred at 50 °C for 15 h. The mixture was cooled to room temperature and diluted with water (10 mL). The phases were separated, and the aqueous layer was extracted with dichloromethane (3×10 mL). The combined organic phases were washed with sodium bicarbonate solution (10 mL), dried over magnesium sulfate and filtrated.
The solvent was removed under reduced pressure and the crude product was absorbed on Celite ® . After flash column chromatography (petroleum ether/diethylether 250:1 v/v) and gel permeation chromatography (toluene) the product 3 was isolated.