Organic binary charge-transfer compounds of 2,2′ : 6′,2′′ : 6′′,6-trioxotriphenylamine and a pyrene-annulated azaacene as donors

Abstract

Three binary charge-transfer (CT) compounds resulting from the donor 2,2′ : 6′,2′′ : 6′′,6-trioxotriphenylamine (TOTA) and the acceptors F₄TCNQ and F₄BQ and of a pyrene-annulated azaacene (PAA) with the acceptor F₄TCNQ are reported. The identity of these CT compounds are confirmed by single-crystal X-ray diffraction as well as by IR, UV-vis-NIR and EPR spectroscopy. X-ray diffraction analysis reveals a 1 : 1 stoichiometry for TOTA·F₄TCNQ, a 2 : 1 donor : acceptor ratio in (TOTA)₂·F₄BQ, and a rare 4 : 1 stoichiometry in (PAA)₄·F₄TCNQ, respectively. Metrical parameters of the donor (D) and acceptor (A) constituents as well as IR spectra indicate full CT in TOTA·F₄TCNQ, partial CT in (TOTA)₂·F₄BQ and only a very modest one in (PAA)₄·F₄TCNQ. Intricate packing motifs are present in the crystal lattice with encaged, π-stacked (F₄TCNQ⁻)₂ dimers in TOTA·F₄TCNQ or mixed D/A stacks in the other two compounds. Their solid-state UV-vis-NIR spectra feature CT transitions. The CT compounds with F₄TCNQ are electrical insulators, while (TOTA)₂·F₄BQ is weakly conducting.