Engineering of Supramolecular H-Bonded Nanopolygons via Self-Assembly of Programmed Molecular Modules

Abstract

Discrete and multicomponent nanoscale noncovalent assemblies on surfaces featuring polygonal porous domains are presented. The molecular engineering concept involves multivalent molecular modules that are preprogrammed to undergo heteromolecular recognition by exploiting complementary multiple H bonds. Two types of molecular modules have been engineered: (i) a linear unit of twofold symmetry exposing two 2,6-di(acylamino)pyridyl [donor-acceptor-donor (DAD)] recognition sites at its extremities with a 180 degree orientation relative to each other and (ii) an angular unit constituted by a 1,3,6,8-tetraethynylpyrene core peripherally functionalized with four uracil groups [acceptor-donor-acceptor (ADA)] positioned at 60 degrees and 120 degrees relative to each other. These molecular modules self-assemble through H-bonds between the complementary recognition sites, forming supramolecular architectures. Their symmetry depends upon the type of each individual subunit and the stoichiometry as well as on the combination and distribution of the main symmetry axes. These so-formed two-dimensional (2D) supramolecular oligomers have been studied in solution by optical spectroscopy and on highly ordered pyrolitic graphite (HOPG) substrates by scanning tunneling microscopy (STM) at the solid-liquid interface. Steady-state UV/vis absorption and emission titration measurements suggest the reversible formation of multiple oligomeric species with slightly modulated fluorescence spectra. This likely reflects the presence of various aggregates between the two polytopic receptors, which exhibit somewhat different electronic delocalization as a function of the aggregate size. The presence of multiple species is further confirmed by time-resolved luminescence measurements: lifetime values are fitted as double/multiple exponentials and are always shorter than 6.5 ns. The formation of several oligomeric species is further supported by in situ STM measurements at the solid-liquid interface that provided evidence, with submolecular resolution, for the formation of multicomponent and discrete 2D polygon-like assemblies. We highlight the role of accurate control of the concentration required to image on the surface the 2D oligomeric species formed in solution, which allows us to bypass the determinant role of the substrate-molecule interactions in forming the thermodynamically stable monocomponent architectures at the solid-liquid interface.

Selective Formation of Bi‐Component Arrays Through H‐Bonding of Multivalent Molecular Modules

“…[58,59] All assembling molecular modules have been synthesized by Sonogashira-type cross-coupling reactions [63] starting from the respective ethynyl derivatives (Scheme 1). Pd-catalyzed crosscoupling reaction between 1-bromo-3,4,5-tri-(dodecyloxy)benzene [64] and ethynyl-pyridine 5 in the presence of copper iodide and [Pd(PPh 3 ) 4 ] afforded molecular module 1.…”

“…Since the aromatic groups attached to the recognition moieties could strongly influence their self-assembly behavior (i.e., the K a ), we investigated the association properties of com- [58,59]. a) One of the three possible homo-association geometries between two uracil end-groups and b) hetero-association geometry between di(acetylamino)-pyridine and uracil residues.…”

“…In this view, the multitopic molecule 3 has been synthesized [59] in order to use a tetrasubstituted pyrene module as a cornerstone for the self-assembly. According to its geometry, one can expect that the recognition and the combination of each uracil unit at the four extremities of molecule 3 with one 2,6-di(acetylamino)pyridine of molecule 1 results in the generation of pentameric species [(1) 4 Á3] www.afm-journal.de displaying a ''Saint Andrew'' cross-like shape.…”

Tuning the hydrogen-bonding strength in 2,6-bis(cycloalkylcarbonylamino)pyridine assemblies by variable flexibility. Association constants measured by hydrogen-bonded vs. non-hydrogen-bonded protons

“…Thus monitoring several nuclei is the method of choice to improve the reliability of obtained results. Triple hydrogen-bonded associates are met in many structures as in DNA [14,15], amides [16,17], artificial sensors [18][19][20][21][22], materials [23], non-covalent polymers [4,[24][25][26][27][28] and in recently observed associates of orotic acid [29,30]. Triple hydrogen-bonded assemblies carrying 2,6-diaminopyridine DAD-hydrogen bonding moiety were studied by some groups with the use of various methods [4,6,[31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] and also by us [48,49].…”

Organic Ambipolar Conjugated Molecules for Electronics: Synthesis and Structure–Property Relationships

“…[62] Organic functional materials originate from the need to engineer matter at the molecular level, resulting in advanced materials that hold great promise for successful applications in many fields. [63] A common approach to obtain these materials is based on polymers blended with luminescent dyes that simultaneously emit over the whole visible range due to partial energy transfer from energy D polymers to A dyes. Recently, a supramolecular concept to white emitting plastic materials has been proposed in which a p-conjugated polymer is encapsulated in a p-organogel.…”