Effect of the ortho alkylation of perylene bisimides on the alignment and self-assembly properties

Aligning self-assembled perylene bisimides in a magnetic field

Photoconductive self-assembled 1D structures can be formed by perylene bisimides. These structures are generally randomly orientated, limiting their applications as conductive wires. Here, we show that magnetic fields can be used to create highly aligned, directionally-dependent thin films. This approach leads to well-aligned structures over large areas.

Improving the Quantum Yields of Perylene Diimide Aggregates by Increasing Molecular Hydrophobicity in Polar Media

Here we report the quantum yield of four aggregated perylene diimide (PDI) species that vary by the length of the branched side chains attached at the N,N' imide positions. The PDI molecules were dissolved in binary water:methanol solvents as a means to vary the solvent polarity and control the degree of aggregation in solution. By performing spectroscopy, kinetics, and light scattering experiments, the nature of the molecular interactions in the solutions was determined. The maximum quantum yield of the aggregated molecules increased from 0.04 for the shortest chain molecule (B2) to 0.20 for the largest chain molecule (B13). The higher quantum yield of B13 compared with B2 correlates well with an increase in the fluorescence lifetime. The monomer emission lifetime was 4.8 ns whereas a lifetime as high as 21.2 ns was measured for the B13 aggregate fluorescence. A shorter sub-nanosecond lifetime was also measured for suspended colloids in B5, B9, and B13. The enhanced quantum yield is attributed to an increase of disorder in the B13 aggregates. As the polarity of the solution increases, the hydrophobic effect further enhances the disorder, and, therefore, the quantum yields in these particles.

Relationship between Side-Chain Polarity and the Self-Assembly Characteristics of Perylene Diimide Derivatives in Aqueous Solution

Perylene-3,4,9,10-tetracarboxylic acid diimides (PDIs) have recently gained considerable interest for water-based biosensing applications. PDIs have been studied intensively in the bulk state, but their physical properties in aqueous solution in interplay with side-chain polarity are, however, poorly understood. Therefore, three perylene diimide based derivatives were synthesized to study the relationship between side-chain polarity and their self-assembly characteristics in water. The polarity of the side chains was found to dictate the size and morphology of the formed aggregates. Side-chain polarity rendered the self-assembly and photophysical properties of the PDIs-both important for imminent water-based applications-and these were revealed to be especially responsive to changes in solvent composition.

Aligning self-assembled gelators by drying under shear

We show how drying under shear can be used to prepare aligned fibres and worm-like micelles from low molecular weight gelators. Shearing followed by drying leads to the dealignment before the water can be removed; continuous shear whilst drying is required to maintain the alignment. Combining a slow pH change with continuous shear allows alignment of the gelling fibres, which can then be dried.

Self-assembly of sodium and potassium betulinates into hydro- and organo-gels: entrapment and removal studies of fluorophores and synthesis of gel–gold nanoparticle hybrid materials

Sodium and potassium salts of a renewable nano-sized triterpenoid betulinic acid have been prepared and their self-assembly properties in water and aqueous solvent mixtures have been studied.

Rapid Energy Transfer Enabling Control of Emission Polarization in Perylene Bisimide Donor-Acceptor Triads

Materials showing rapid intramolecular energy transfer and polarization switching are of interest for both their fundamental photophysics and potential for use in real-world applications. Here, we report two donor-acceptor-donor triad dyes based on perylene-bisimide subunits, with the long axis of the donors arranged either parallel or perpendicular to that of the central acceptor. We observe rapid energy transfer (<2 ps) and effective polarization control in both dye molecules in solution. A distributed-dipole Förster model predicts the excitation energy transfer rate for the linearly arranged triad but severely underestimates it for the orthogonal case. We show that the rapid energy transfer arises from a combination of through-bond coupling and through-space transfer between donor and acceptor units. As they allow energy cascading to an excited state with controllable polarization, these triad dyes show high potential for use in luminescent solar concentrator devices.