Supramolecular nanostructures

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Quenching of fluorescence of aromatic molecules by graphene due to electron transfer

Investigations on the fluorescence quenching of graphene have been carried out with two organic donor molecules, pyrene butanaoic acid succinimidyl ester (PyBS, I) and oligo(p-phenylenevinylene) methyl ester (OPV-ester, II). Absorption and photoluminescence spectra of I and II recorded in mixture with increasing the concentrations of graphene showed no change in the former, but remarkable quenching of fluorescence. The property of graphene to quench fluorescence of these aromatic molecules is shown to be associated with photo-induced electron transfer, on the basis of fluorescence decay and time-resolved transient absorption spectroscopic measurements.Comment: 18 pages, 6 figure

Self-assembled nanotapes of oligo(p-phenylene vinylene)s: sol-gel-controlled optical properties in fluorescent π-electronic gels

A rational approach to the design of supramolecular organogels of all-trans oligo(p-phenylene vinylene) (OPV) derivatives, a class of well-known organic semiconductor precursors, is reported. Self-assembly of these molecules induced gelation of hydrocarbon solvents at low concentrations (<1 mM), resulting in high aspect ratio nanostructures. Electron microscopy and atomic force microscopy (AFM) studies revealed twisted and entangled supramolecular tapes of an average of 50-200 nm in width, 12-20 nm in thickness, and several micrometers in length. The hierarchical growth of the entangled tapes and the consequent gelation is attributed to the lamellar-type packing of the molecules, facilitated by cooperative hydrogen bonding, πstacking, and van der Waals interactions between the OPV units. Gelation of OPVs induced remarkable changes in the absorption and emission properties, which indicated strong electronic interaction in the aggregated chromophores. Comparison of the absorption and emission spectra in the gel form and in the solid film indicated a similar chromophore organization in both phases. The presence of self-assembled aggregates of OPVs was confirmed by solvent- and temperature-dependent changes in the absorption and emission properties, and by selective excitation experiments. This is the first detailed report of the gelation-induced formation of OPV nanotapes, assisted by weak, nondirectional hydrogen-bonding motifs and π-π stacking. These findings may provide opportunities for the design of a new class of functional soft materials and nanoarchitectures, based on π-conjugated organic semiconductor-type molecules, thereby enabling the manipulation of their optical properties

Gelation-assisted light harvesting by selective energy transfer from an oligo(p-phenylenevinylene)-based self-assembly to an organic dye

Hot gels get turned off: Gelation of the title molecules facilitate transfer of excitation energy exclusively from the self-assembled nanostructures (see scheme path a) to Rhodamine B and not from the single molecules (path b), thereby establishing the role of self-assembled gel nanostructures in light harvesting. The emission from the dye can be shut off in a thermoreversible fashion since the self-assembly breaks to form molecular, dissolved oligo(phenylenevinylene)s above the gel melting temperature (T_gel)