Effect of Steric Complementarity on Solid-State Optical Properties of Ternary CT Complexes: 4,4′-Biphenyldisulfonic Acid, Aliphatic Amines, and Tetracyanoquinodimethane

Crystalline ternary charge transfer (CT) complexes were constructed for tuning colors by a supramolecular approach. The complexes are composed of 4,4′-biphenyldisulfonic acid (BPDS, donor), tetracyanoquinodimethane (TCNQ, acceptor), and aliphatic amines. Four salts of BPDS with methyl-, ethyl-, isopropyl-, or t-butylamine underwent insertion of TCNQ between biphenyl moieties to yield the CT complexes with different colors in a range of deep red to light orange. Such a color change was interpreted on the basis of crystal structures of the complexes. BPDS salts produce layer structures which provide nanospaces for TCNQ and alkyl groups. Steric complementarity in the nanospaces explains the above-mentioned color change.