Synthesis and Properties of Archetypical Donor-Acceptor-Donor (D²A) Molecules

The primary objective of the present investigation was to study a class of compounds in which two donors and one acceptor (D₂A) are parts of the same molecule: 3a-e. Systematic variation of the donor moiety (ArCH₂; Ar = C₆H₅, p-MeOC₆H₄, p-NO₂C₆H₄, β-naphthyl, p-NH₂C₆H₄ (3a-e)) leads to a series of compounds that behave in solution to a large extent like substituted TCNQ molecules. In contrast, the isomorphous mode of aggregation in the solid state for 3a, 3b, and 3d indicates a strong driving force toward segregated stacking of the TCNQ moieties, a packing arrangement not observed in other TCNQ derivatives. The solid-state spectral properties also indicate the crucial role of the mode of aggregation. The relevance of these compounds to an overall strategy of design of organic conducting materials is discussed.