A DNA-Based Light-Harvesting Antenna

Two-Dimensional Excitonic Networks Directed by DNA Templates as an Efficient Model Light-Harvesting and Energy Transfer System

Photosynthetic organisms organize discrete light-harvesting complexes into large-scale networks to facilitate efficient light collection and utilization. Inspired by nature, herein, synthetic DNA templates were used to direct the formation of dye aggregates with a cyanine dye, K21, into discrete branched photonic complexes, and two-dimensional (2D) excitonic networks. The DNA templates ranged from four-arm DNA tiles, ≈10 nm in each arm, to 2D wireframe DNA origami nanostructures with different geometries and varying dimensions up to 100×100 nm. These DNA-templated dye aggregates presented strongly coupled spectral features and delocalized exciton characteristics, enabling efficient photon collection and energy transfer. Compared to the discrete branched photonic systems templated on individual DNA tiles, the interconnected excitonic networks showed approximately a 2-fold increase in energy transfer efficiency. This bottom-up assembly strategy paves the way to create 2D excitonic systems with complex geometries and engineered energy pathways.

Highly Efficient Artificial Light-Harvesting Systems Constructed in Aqueous Solution Based on Supramolecular Self-Assembly

Highly efficient light-harvesting systems were successfully fabricated in aqueous solution based on the supramolecular self-assembly of a water-soluble pillar[6]arene (WP6), a salicylaldehyde azine derivative (G), and two different fluorescence dyes, Nile Red (NiR) or Eosin Y (ESY). The WP6-G supramolecular assembly exhibits remarkably improved aggregation-induced emission enhancement and acts as a donor for the artificial light-harvesting system, and NiR or ESY, which are loaded within the WP6-G assembly, act as acceptors. An efficient energy-transfer process takes place from the WP6-G assembly not only to NiR but also to ESY for these two different systems. Furthermore, both of the WP6-G-NiR and WP6-G-ESY systems show an ultrahigh antenna effect at a high donor/acceptor ratio.

Protein-Framed Multi-Porphyrin Micelles for a Hybrid Natural-Artificial Light-Harvesting Nanosystem

A micelle-like hybrid natural-artificial light-harvesting nanosystem was prepared through protein-framed electrostatic self-assembly of phycocyanin and a four-armed porphyrin star polymer. The nanosystem has a special structure of pomegranate-like unimolecular micelle aggregate with one phycocyanin acceptor in the center and multiple porphyrin donors in the shell. It can inhibit donor self-quenching effectively and display efficient transfer of excitation energy (about 80.1 %) in water. Furthermore, the number of donors contributing to a single acceptor could reach as high as about 179 in this nanosystem.

DNA-Based Oligochromophores as Light-Harvesting Systems

The chromophores ethynyl pyrene as blue, ethynyl perylene as green and ethynyl Nile red as red emitter were conjugated to the 5-position of 2'-deoxyuridine via an acetylene bridge. Using phosphoramidite chemistry on solid phase labelled DNA duplexes were prepared that bear single chromophore modifications, and binary and ternary combinations of these chromophore modifications. The steady-state and time-resolved fluorescence spectra of all three chromophores were studied in these modified DNA duplexes. An energy-transfer cascade occurs from ethynyl pyrene over ethynyl perylene to ethynyl Nile red and subsequently an electron-transfer cascade in the opposite direction (from ethynyl Nile red to ethynyl perylene or ethynyl pyrene, but not from ethynyl perylene to ethynyl pyrene). The electron-transfer processes finally provide charge separation. The efficiencies by these energy and electron-transfer processes can be tuned by the distances between the chromophores and the sequences. Most importantly, excitation at any wavelength between 350 and 700 nm finally leads to charge separated states which make these DNA samples promising candidates for light-harvesting systems.

G-quartet-based nanostructure for mimicking light-harvesting antenna

Artificial light-harvesting systems have received great attention for use in photosynthetic and optoelectronic devices. Herein, a system involving G-quartet-based hierarchical nanofibers generated from the self-assembly of guanosine 5'-monophosphate (GMP) and a two-step Förster resonance energy transfer (FRET) is presented that mimics natural light-harvesting antenna. This solid-state property offers advantages for future device fabrication. The generation of photocurrent under visible light shows it has potential for use as a nanoscale photoelectric device. The work will be beneficial for the development of light-harvesting systems by the self-assembly of supramolecular nanostructures.

Self-assembly of DNA-oligo(p-phenylene-ethynylene) hybrid amphiphiles into surface-engineered vesicles with enhanced emission

Surface-addressable nanostructures of linearly π-conjugated molecules play a crucial role in the emerging field of nanoelectronics. Herein, by using DNA as the hydrophilic segment, we demonstrate a solid-phase "click" chemistry approach for the synthesis of a series of DNA-chromophore hybrid amphiphiles and report their reversible self-assembly into surface-engineered vesicles with enhanced emission. DNA-directed surface addressability of the vesicles was demonstrated through the integration of gold nanoparticles onto the surface of the vesicles by sequence-specific DNA hybridization. This system could be converted to a supramolecular light-harvesting antenna by integrating suitable FRET acceptors onto the surface of the nanostructures. The general nature of the synthesis, surface addressability, and biocompatibility of the resulting nanostructures offer great promises for nanoelectronics, energy, and biomedical applications.

Gated electron sharing within dynamic naphthalene diimide-based oligorotaxanes

The controlled self-assembly of well-defined and spatially ordered π-systems has attracted considerable interest because of their potential applications in organic electronics. An important contemporary pursuit relates to the investigation of charge transport across noncovalently coupled components in a stepwise fashion. Dynamic oligorotaxanes, prepared by template-directed methods, provide a scaffold for directing the construction of monodisperse one-dimensional assemblies in which the functional units communicate electronically through-space by way of π-orbital interactions. Reported herein is a series of oligorotaxanes containing one, two, three and four naphthalene diimide (NDI) redox-active units, which have been shown by cyclic voltammetry, and by EPR and ENDOR spectroscopies, to share electrons across the NDI stacks. Thermally driven motions between the neighboring NDI units in the oligorotaxanes influence the passage of electrons through the NDI stacks in a manner reminiscent of the conformationally gated charge transfer observed in DNA.

DNA polyfluorophores for real-time multicolor tracking of dynamic biological systems

Dye-ing to live: Spectral limitations of common organic dyes make it difficult or impossible to visualize and follow multiple biological components in rapidly moving systems. The development of a multispectral set of improved DNA-scaffolded fluorophores is described. Their use in multicolor cellular imaging (see scheme) and in tracking of biological motions on the subsecond timescale is demonstrated.