Counterion-dependent valence tautomerization of ferrocenyl-conjugated pyrylium salts

1-Ferrocenylethynylanthraquinone, which is a donor (D)-acceptor conjugated compound consisting of a ferrocene (Fc) acting as a donor, an anthraquinone (Aq) acting as an acceptor, and an ethynyl linker, has undergone a cyclocondensation reaction with strong organic acid and has formed 2-ferrocenyloxodihydrodibenzochromenylium salts are characterized as conjugated donor-acceptor compounds. The studies have shown that the electrostatic interaction between the 2-ferrocenyloxodihydrodibenzochromenylium moiety and the counteranion might affect the occurrence of variable-temperature (VT).