Molecular Self-Assemblies in Co-Crystals: Engineering Chemical Reactivity and Organic Semiconductors - Molecular Self-Assembly: Advances and Applications - page 227

Scheme 7.3 Stacking in the solid state: (a) intermolecular [2 + 2]

photodimerization of cinnamic acid and (b) face-to-face and
edge-to-face geometries for semiconductor molecules.

Aromatic molecules, however, frequently exhibit edge-to-face, as
opposedtoface-to-face,stackinginthesolidstate(Scheme7.3)[10].
Consequently,therehavebeenmanyefortstodevelopmethodsthat
guide the assembly of aromatics into face-to-face geometries so as
to control the chemical reactivity and charge mobility. A majority of
approacheshavereliedontheuseofsubstituentstoafectpacking
via attractive (e.g., hydrogen bonds, halogen-halogen interactions,
charge-transfer forces) [11,12], as well as repulsive (e.g., steric) [13],
noncovalentforces.Suchasubstituent-basedapproach,however,has
haddifficultiescompetingwiththesubtlestructuredemandsofdense
crystal packing, which is the driving force that provides the cohesive
energy for crystallization [14]. In this context, we hypothesized that
a CCF with a structure largely preorganized to assemble aromatics
intofiniteassembliescouldconfrontthepackingproblemtoprovide
a means to direct reactivity and achieve stacking of semiconductor
moleculesinsolids(Scheme7.4).Bydirectingchemicalreactivity,
the CCF would serve the role of a small-molecule template.

Scheme 7.4 SchematicofusingaCCFtocontrol:(a)reactivityand(b)

mobility.