Cover Feature: Structure-Packing-Property Correlation of Self-Sorted Versus Interdigitated Assembly in TTF⋅TCNQ-Based Charge-Transport Materials (Chem. Eur. J. 47/2018)

Abstract

Among the various donor-acceptor (D-A) charge transfer cocrystals investigated in the past few decades, tetrathiafulvalene-tetracyanoquinodimethane (F.Q, popularly known as TTF.TCNQ) based cocrystals have fascinated materials chemists owing to its packing and exceptional properties. Here, crystallographic information files of eighteen F.Q based cocrystals were extracted from Cambridge Structural Database and classified into Class 1 (D on D and A on A segregated stacks; F.Q, F1.Q - F6.Q and F.Q1), Class 2 (-A-D-A-D-A-D- mixed stacks; F6a.Q - F11.Q and F.Q2) and Class 3 (-A-D-A-A-D-A-; Class 3a (F12.Q and F13.Q) and -D-D-A-A-D-D-; Class 3b (F14.Q)) systems based on their packing modes. PIXEL calculations revealed that the Q on Q dimer is the energetically most favored dimer in F.Q, the substituents on F capable of forming hydrogen bonding, C...S and other weak intermolecular interactions resulted in the greater stability of F on F dimer for F1.Q - F6.Q (except F2.Q). Band structure of F.Q and F6.Q with high interaction of electronic orbitals between D on D and A on A in segregated stacks were found to be metal-like (band gap, Eg = 0.003 eV) and metallic (overlapping bands in the Fermi level) respectively while the polymorph of F6.Q belonging to Class 2 (F6a.Q) displayed a semiconductor-type band structure (Eg = 0.053 eV). F12.Q of Class 3a exhibited a metal-like band structure (Eg = 0.001 eV).