Solid-State Packing of Conjugated Oligomers: From π-Stacks to the Herringbone Structure

The solid-state structures of a series of bithiazole and thiophene oligomers, as well as a series
of substituted pentacenes, are rationalized in terms of “pitch and roll” inclinations from an “ideal” cofacial
π-stack. Pitch inclinations translate adjacent molecules relative to one another in the direction of the long
molecular axis, whereas roll inclinations translate the molecules along the short molecular axis. Thus,
moderately large pitch distortions preserve π−π interactions between adjacent molecules, whereas roll
translations greater than 2.5 Å essentially destroy π−π overlap between adjacent molecules. The familiar
herringbone packing is characterized by large roll distortions. It is shown that thiophenes tend to exhibit
large roll translations, whereas thiazoles have small roll but large pitch translations. Substituted pentacenes
tend to have both moderate pitch and roll distances. The relationship of molecular packing to transport
properties is discussed.