James E. A. Webb

Thermodynamic Factors Impacting the Peptide-Driven Self-Assembly of Perylene Diimide Nanofibers

Synthetic peptides offer enormous potential to encode the assembly of molecular electronic components, provided that the complex range of interactions is distilled into simple design rules. Here, we report a spectroscopic investigation of aggregation in an extensive series of peptide-perylene diiimide conjugates designed to interrogate the effect of structural variations. By fitting different contributions to temperature dependent optical absorption spectra, we quantify both the thermodynamics and the nature of aggregation for peptides by incrementally varying hydrophobicity, charge density, length, as well as asymmetric substitution with a hexyl chain, and stereocenter inversion. We find that coarse effects like hydrophobicity and hexyl substitution have the greatest impact on aggregation thermodynamics, which are separated into enthalpic and entropic contributions. Moreover, significant peptide packing effects are resolved via stereocenter inversion studies, particularly when examining the nature of aggregates formed and the coupling between π electronic orbitals. Our results develop a quantitative framework for establishing structure-function relationships that will underpin the design of self-assembling peptide electronic materials.

Limitations and design considerations for donor–acceptor systems in luminescent solar concentrators: the effect of coupling-induced red-edge absorption

Luminescent solar concentrators (LSCs) use luminescence and waveguiding to concentrate photons within thin dielectric slabs for use in photovoltaic, lighting, and photobioreactor applications. Donor–acceptor systems of organic chromophores are widely used in LSCs to broaden the sunlight absorption range and attempt to reduce loss-inducing reabsorption by the emitting chromophore. We use raytrace simulations across a large parameter space to model the performance of LSCs containing two novel donor–acceptor trimers based on the perylene moiety. We find that under certain conditions, trimers outperform single-dye LSCs as expected. However, at higher concentrations, a slight increase in red-edge absorption by the trimers increases reabsorption and has a deleterious effect on LSC performance. This underscores the large effect that even small changes in the red edge can have, and may discourage the use of donor–acceptor schemes with high interchromophore coupling that promotes red-edge absorption. Finally, we show that for a LSC-PV pair, selecting a PV cell that is well-matched with the LSC emission spectrum has a large effect on the flux gain of the system, and that the systems studied here are well-matched to emerging PV technologies.

Halogen bonding influences perylene-core twists in non-core substituted perylene tetraesters

Halogen bonding has emerged as a popular synthon in supramolecular architectures. Its effects on supramolecular perylene systems however have been under investigated. We report X⋯O halogen bonding of perylene-3,4,9,10-tetracarboxylic tetra esters. This templates a twisted perylene core which affects its spectral properties. We show this interaction exists in both the solution and solid state through spectroscopy studies and single crystal analysis.

Chiral effects in peptide-substituted perylene imide nanofibres

A series of peptide-functionalised perylene imide molecules was studied to examine the effect of peptide chirality on the self-assembly of the perylene imides core into nanofibres. Peptide stereogenic positions, stereochemical configurations, amphiphilic substitution and perylene core modification were spectroscopically evaluated with respect to chiral assembly. For dipeptide molecules, stereocenters in peptide residue positions proximal to the perylene core (1–5 units) were found to impart helical chirality to the perylene core, while stereocenters in more distal residue positions did not exert a chiral influence. Diastereomers involving stereocenter inversions within the proximal residues consequently manifested spectroscopically as pseudo-enantiomers. Increased side-chain steric demand in the proximal positions gave similar chiral influence but exhibited diminished Cotton effect intensity with additional longer wavelength features attributed to interchain excimers. Replacing one of the two peptide substituents with an alkyl chain to create strongly amphiphilic perylene bisimides disrupted chiral self-assembly. On the other hand, amphiphilic structures achieved through the modification of the perylene imide core with a bisester moiety prompted strongly exciton-coupled, solvent-responsive self-assembly into long, chiral nanofilaments.

Capturing ultrafast spectral evolution with transient grating photoluminescence spectroscopy

We have developed a new method, transient grating photoluminescence spectroscopy (TGPLS), allowing the collection of broadband ultrafast photoluminescence spectroscopy with low photoluminescence background. In TGPLS, two ultrafast laser pulses generate a multiplexed transient grating (TG) by the optical Kerr effect. The gated signal is diffracted by the TG and spatially separated from background fluorescence. This high performance nonlinear optical gate delivers time resolution less than 200 fs, spectral bandwidth covering the entire visible region with extremely low fluorescence background. Here we present two applications of TGPLS that provide deeper insight into ultrafast energy transfer in multi-chromophore perylene arrays and ultrafast structural relaxation in oligothiophenes.

Using multi-function components to solve optical design challenges for DUV microlithographic applications

Several small-field catadioptric optical designs have been developed over the last decade to meet the demanding needs from lithographers. Design solutions that use a multi-function component can provide nearly perfect wavefront correction for optical systems with broad bandwidth sources, such as free running (un-narrowed) excimer lasers operating at wavelengths below 300 nm, with limited choices of optical materials with high transmission at these wavelengths. From these catadioptric design forms, variations have been developed to accommodate changes in wavelength, increases in the numerical aperture and conversion of the imaging medium from nitrogen to ultra-high purity water and other high index fluids for immersion lithography applications. Some designs also address the need for increased working distance. This paper will discuss the use of multi-function components, the evolution of several design forms, the optical materials required, their benefits for specific applications, and the challenges they have created.