T. Marangoni, S. A. Mezzasalma, A. Llanes-Pallas, K. Yoosaf, N. Armaroli, D. Bonifazi,
Langmuir 2011, 27, 1513-1523
The ability of two complementary molecular modules bearing H-bonding uracilic and 2,6-(diacetylamino)pyridyl moieties to self-assemble and self-organize into submicrometer morphologies has been investigated by means of spectroscopic, thermogravimetric, and microscopic methods. Using uracilic 3N-BOC-protected modules, it has been possible to thermally trigger the self-assembly/self-organization process of the two molecular modules, inducing the formation of objects on a mica surface that exhibit crater-like morphology and a very homogeneous size distribution. Confirmation of the presence of the hydrogen-bonding-driven self-assembly/self-organization process in solution was obtained by variable-temperature (VT) steady-state UV−vis absorption and emission measurements. The variation of the geometric and spatial features of the morphologies was monitored at different T by means of atomic force microscopy (AFM) and was interpreted by a nonequilibrium diffusion model for two chemical species in solution. The formation of nanostructures turned out to be affected by the solid substrate (molecular interactions at a solid−liquid interface), by the matter-momentum transport in solution (solute diffusivity D0 and solvent kinematic viscosity ν), and the thermally dependent cleavage reaction of the BOC functions (T-dependent differential weight loss, θ = θ(Τ)) in a T interval extrapolated to ∼60 K. A scaling function, f = f (νD0, ν/D0, θ), relying on the onset condition of a concentration-driven thermosolutal instability has been established to simulate the T-dependent behavior of the structural dimension (i.e., height and radius) of the self-organized nanostructures as ⟨h⟩ ≈ f (T) and ⟨r⟩ ≈ 1/f (T).