title: From molecular to macroscopic engineering: shaping hydrogen-bonded organic nanomaterials.
abstract: The self-assembly and self-organization behavior of chromophoric acetylenic scaffolds bearing 2,6-bis(acetylamino)pyridine (1, 2) or uracyl-type (3-9) terminal groups has been investigated by photophysical and microscopic methods. Systematic absorption and luminescence studies show that 1 and 2, thanks to a combination of solvophilic/solvophobic forces and π-π stacking interactions, undergo self-organization in apolar solvents (i.e., cyclohexane) and form spherical nanoparticles, as evidenced by wide-field optical microscopy, TEM, and AFM analysis. For the longer molecular module, 2, a more uniform size distribution is found (80-200 nm) compared to 1 (20-1000 nm). Temperature scans in the range 283-353 K show that the self-organized nanoparticles are reversibly formed and destroyed, being stable at lower temperatures. Molecular modules 1 and 2 were then thoroughly mixed with the complementary triply hydrogen-bonding units 3-9. Depending on the specific geometrical structure of 3-9, different nanostructures are evidenced by microscopic investigations. Combination of modules 1 or 2 with 3, which bears only one terminal uracyl unit, leads to the formation of vesicular structures; instead, when 1 is combined with bis-uracyl derivative 4 or 5, a structural evolution from nanoparticles to nanowires is observed. The length of the wires obtained by mixing 1 and 4 or 1 and 5 can be controlled by addition of 3, which prompts transformation of the wires into shorter rods. The replacement of linear system 5 with the related angular modules 6 and 7 enables formation of helical nanostructures, unambiguously evidenced by AFM. Finally, thermally induced self-assembly was studied in parallel with modules 8 and 9, in which the uracyl recognition sites are protected with tert-butyloxycarbonyl (BOC) groups. This strategy allows further control of the self-assembly/self-organization process by temperature, since the BOC group is completely removed on heating. Microscopy studies show that the BOC-protected ditopic modules 8 self-assemble and self-organize with 1 into ordered linear nanostructures, whereas BOC-protected tritopic system 9 gives rise to extended domains of circular nano-objects in combination with 1.
authors.affiliation: Molecular Photoscience Group, Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche (CNR-ISOF), Via Gobetti 101, 40129 Bologna, Italy.
authors.forename: K
authors.initials: K
authors.lastname: Yoosaf
authors.forename: Anna
authors.initials: A
authors.lastname: Llanes-Pallas
authors.forename: Tomas
authors.initials: T
authors.lastname: Marangoni
authors.forename: Abdelhalim
authors.initials: A
authors.lastname: Belbakra
authors.forename: Riccardo
authors.initials: R
authors.lastname: Marega
authors.forename: Edith
authors.initials: E
authors.lastname: Botek
authors.forename: Benoît
authors.initials: B
authors.lastname: Champagne
authors.forename: Davide
authors.initials: D
authors.lastname: Bonifazi
authors.forename: Nicola
authors.initials: N
authors.lastname: Armaroli
mesh_terms: D006860:Hydrogen Bonding; D018625:Microscopy, Atomic Force; D053758:Nanoparticles / Q000737:chemistry; D049329:Nanostructures / Q000737:chemistry*; D053770:Nanowires / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013696:Temperature; D014498:Uracil / Q000737:chemistry
chemical_list: D011725:Pyridines; D012997:Solvents; D014498:Uracil; C023666:pyridine