A benzotrithiophene derivative possessing
phenylisoxazoles self-assembled
to form stacks. The molecule isodesmically self-assembled in chloroform,
whereas it self-assembled in a cooperative fashion in decalin and
in methylcyclohexane. Thermodynamic studies based on isodesmic, van
der Schoot, and Goldstein–Stryer mathematical models revealed
that the self-assembly processes are enthalpically driven and entropically
opposed. An enthalpy–entropy compensation plot indicates that
the assembly processes in chloroform, decalin, and methylcyclohexane
are closely related. The enthalpic gains in less-polar solvents are
greater than those in more-polar solvents, resulting in the formation
of large assemblies in decalin and in methylcyclohexane. The formation
of large assemblies leads to cooperative assemblies. The elongation
process is enthalpically more favored than the nucleation process,
which drives the cooperativity of the self-assembly. DFT calculations
suggested that a hexameric assembly is more stable than tetrameric
or dimeric assemblies. Cooperative self-assemblies based on intermolecular
interactions other than hydrogen bonding have rarely been reported.
It is demonstrated herein that van der Waals interactions, including
induced dipole–dipole interactions, can drive the cooperative
assembly of planar π-conjugated molecules