Sculpting photoproducts with DNA origami.

Natural light-harvesting systems spatially organize densely packed dyes in different configurations to either transport excitons or convert them into charge photoproducts, with high efficiency. In contrast, artificial photosystems like organic solar cells and light-emitting diodes lack this fine structural control, limiting their efficiency. Thus, biomimetic multi-dye systems are needed to organize dyes with the sub-nanometer spatial control required to sculpt resulting photoproducts.

Peer support during in vivo exposure homework increases likelihood of prolonged exposure therapy completion.

Exposure-based treatments such as prolonged exposure therapy (PE) are effective for veterans with PTSD. However, dropout rates as high as 50% are common. The Department of Veterans Affairs employs peers to increase mental health treatment engagement, however peers are not routinely used to help patients complete PE homework assignments.

Observation of parallel intersystem crossing and charge transfer-state dynamics in [Fe(bpy)] from ultrafast 2D electronic spectroscopy.

Transition metal-based charge-transfer complexes represent a broad class of inorganic compounds with diverse photochemical applications. Charge-transfer complexes based on earth-abundant elements have been of increasing interest, particularly the canonical [Fe(bpy)]. Photoexcitation into the singlet metal-ligand charge transfer (MLCT) state is followed by relaxation first to the ligand-field manifold and then to the ground state.

Elucidating interprotein energy transfer dynamics within the antenna network from purple bacteria.

In photosynthesis, absorbed light energy transfers through a network of antenna proteins with near-unity quantum efficiency to reach the reaction center, which initiates the downstream biochemical reactions. While the energy transfer dynamics within individual antenna proteins have been extensively studied over the past decades, the dynamics between the proteins are poorly understood due to the heterogeneous organization of the network. Previously reported timescales averaged over such heterogeneity, obscuring individual interprotein energy transfer steps.

Engineering Exciton Dynamics with Synthetic DNA Scaffolds.

Excitons are the molecular-scale currency of electronic energy. Control over excitons enables energy to be directed and harnessed for light harvesting, electronics, and sensing. Excitonic circuits achieve such control by arranging electronically active molecules to prescribe desired spatiotemporal dynamics.

Activating charge-transfer state formation in strongly-coupled dimers using DNA scaffolds.

Strongly-coupled multichromophoric assemblies orchestrate the absorption, transport, and conversion of photonic energy in natural and synthetic systems. Programming these functionalities involves the production of materials in which chromophore placement is precisely controlled. DNA nanomaterials have emerged as a programmable scaffold that introduces the control necessary to select desired excitonic properties.

Tuning Optical Absorption and Emission Using Strongly Coupled Dimers in Programmable DNA Scaffolds.

Molecular materials for light harvesting, computing, and fluorescence imaging require nanoscale integration of electronically active subunits. Variation in the optical absorption and emission properties of the subunits has primarily been achieved through modifications to the chemical structure, which is often synthetically challenging. Here, we introduce a facile method for varying optical absorption and emission properties by changing the geometry of a strongly coupled Cy3 dimer on a double-crossover (DX) DNA tile.

Identification of Nonradiative Decay Pathways in Cy3.

Photoexcited fluorescent markers are extensively used in spectroscopy, imaging, and analysis of biological systems. The performance of fluorescent markers depends on high levels of emission, which are limited by competing nonradiative decay pathways. Small-molecule fluorescent dyes have been increasingly used as markers due to their high and stable emission.

Effect of nanotube coupling on exciton transport in polymer-free monochiral semiconducting carbon nanotube networks.

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are attractive light-harvesting components for solar photoconversion schemes and architectures, and selective polymer extraction has emerged as a powerful route to obtain highly pure s-SWCNT samples for electronic applications. Here we demonstrate a novel method for producing electronically coupled thin films of near-monochiral s-SWCNTs without wrapping polymer. Detailed steady-state and transient optical studies on such samples provide new insights into the role of the wrapping polymer on controlling intra-bundle nanotube-nanotube interactions and exciton energy transfer within and between bundles.

Femtosecond stimulated Raman evidence for charge-transfer character in pentacene singlet fission.

Singlet fission is a spin-allowed process in which an excited singlet state evolves into two triplet states. We use femtosecond stimulated Raman spectroscopy, an ultrafast vibrational technique, to follow the molecular structural evolution during singlet fission in order to determine the mechanism of this process. In crystalline pentacene, we observe the formation of an intermediate characterized by pairs of excited state peaks that are red- and blue-shifted relative to the ground state features.