Synthesis, crystal structures, optical properties, and photocurrent response of heteroacene derivatives

Abstract

Six 5,9,14,18-tetrathiaheptacene derivatives (1 a-1 f) were synthesized by using a simple ether-ether exchange reaction and fully characterized. In contrast to the planar conformation usually observed in thiophene-fused benzene systems, single-crystal analysis indicates that 7,16-dipropyl-5,9,14,18-tetrathiaheptacene (1 a), 7,16-diphenyl-5,9,14,18-tetrathiaheptacene (1 b), and 7,16-di(4'-chlorophenyl)-5,9,14,18-tetrathiaheptacene (1 c) adopt chair conformations. The as-formed dihedral angle between anthracene and the terminal benzene units are 137.258, 137.855, and 134.912° for 1 a, 1 b, and 1 c, respectively, which is close to the theoretical optimization results (128° for 1 b). Interestingly, the oxidized product of 7,16-di(trifluoromethylphenyl)-5,9,14,18-tetrathiaheptacene (1 e) has a saddle shape, which results in the formation of column-shaped units in the single crystal. The substituents on the side phenyl group have less effect on their UV/Vis absorption spectra, but a distinct redshift that accounts for the intramolecular charge transfer can be observed in the emission spectra. The electrochemical measurements show that all compounds present two oxidation waves. The photoswitching behavior based on 1 a-1 f was further measured and the experimental results suggest that these heteroacene derivatives are promising semiconductor materials for organic electronics.

Keywords: X-ray diffraction; acene; conformation analysis; optical properties; semiconductors.