Synthesis and Investigation of the Effect of Substitution on the Structure, Physical Properties, and Electrochemical Properties of Anthracenodifuran Derivatives

A series of syn/anti mixtures
of anthradifuran (ADF) and substituent compounds were systematically
synthesized, and the effect of substitution at the 5,11-positions
on the neutral and radical states of ADF was investigated. All compounds
were measured and analyzed by absorption and fluorescence spectroscopy,
cyclic voltammetry, electrochemical absorption spectroscopy, and DFT
calculations. The absorption spectra of 5,11-substituent compounds
in their neutral state were red-shifted. In addition, the substituted
compounds exhibited increased thermal stability with respect to the
parent 1a because of elongation of the π-conjugation
and an increased steric hindrance effect due to the bulky ethynyl
substituent groups. The cyclic voltammograms of all of the compounds
exhibited irreversible reduction potentials and irreversible oxidation
potentials, except in the case of (trimethylsilyl)­silylethynyl-substituted
ADF. When the materials were subjected to oxidation/reduction potentials,
the radical cation and anion species were generated. The absorption
spectra of the radical-cation species of the compounds exhibited similar
characteristics and similar absorption ranges (550–1400 nm),
whereas the spectra of the radical anion species were blue-shifted
(550–850 nm) compared than that of the parent 1a•– (550–1100 nm). The
DFT computation results suggested that the radical states of lowest
energy transitions occurred primarily from π to πSOMO or from πSOMO to π*.