Tetraalkoxyphenanthrene-fused dehydroannulenes: synthesis, self-assembly, and electronic, optical, and electrochemical properties.

Novel tetraalkoxyphenanthrene-fused dehydro[12]-, [18]-, and [24]annulenes 1-3 were synthesized by using Cu-mediated or Pd-catalyzed oxidative macrocyclization reactions as key steps, and their electronic, optical, and electrochemical properties have been investigated in detail. X-ray crystallographic analysis of a single crystal of 1 a demonstrated that the molecules were arranged longitudinally in a slipped π-stacked fashion to form a 1D column. (1)H NMR and UV/Vis spectroscopic and cyclic voltammetric analysis in conjugation with nucleus-independent chemical shift (NICS) calculations for 1-3 support that the annulation at the 9,10-positions of phenanthrene to the dehydroannulene ring enhances the tropicity and decreases the HOMO-LUMO gaps of the molecules relative to the benzannulation and that 1 possesses an antiaromatic character. Self-association behavior due to π-π stacking in CDCl3 was observed for 1 and 2 and was quantified by concentration-dependent (1)H NMR spectroscopic measurements. The self-assembly of 1 and 2 into well-defined 1D superstructures with high aspect ratios were obtained, and the morphology and crystallinity of these compounds were investigated by means of SEM and wide-angle X-ray diffraction (WAXD) measurements. Furthermore, it was shown that 1 b and 2 b display liquid-crystalline phases by means of differential scanning calorimetry, polarizing optical microscopy, and variable-temperature WAXD measurements.