Crystal Growth, Structure, and Transport Properties of the Charge-Transfer Salt Picene/2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane

Single
crystals of the charge-transfer salt picene/2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane
have been grown using physical vapor transport. The crystal structure
was determined using single-crystal X-ray diffraction. It was found
that the crystals grow in a 1:1 molecular ratio and adopt a monoclinic
structure with alternate stacking. Both X-ray data and Raman measurements
show that the grown crystals are of good quality. From structure and
infrared data, the charge transfer between acceptor and donor molecules
was estimated to be approximately 0.14–0.19 electron. Transport
measurements indicate a nonmetallic ground state with an activation
energy of 0.6 eV. The supporting density functional theory calculations
on molecular model systems as well as on crystalline structures confirm
the amount of charge transfer and provide first insights into the
electronic structure of the new material.