3 research outputs found
Coherent Exciton Delocalization in a Two-State DNA-Templated Dye Aggregate System
Coherent exciton
delocalization in dye aggregate systems gives
rise to a variety of intriguing optical phenomena, including J- and
H-aggregate behavior and Davydov splitting. Systems that exhibit coherent
exciton delocalization at room temperature are of interest for the
development of artificial light-harvesting devices, colorimetric detection
schemes, and quantum computers. Here, we report on a simple dye system
templated by DNA that exhibits tunable optical properties. At low
salt and DNA concentrations, a DNA duplex with two internally functionalized
Cy5 dyes (i.e., dimer) persists and displays predominantly J-aggregate
behavior. Increasing the salt and/or DNA concentrations was found
to promote coupling between two of the DNA duplexes via branch migration,
thus forming a four-armed junction (i.e., tetramer) with H-aggregate
behavior. This H-tetramer aggregate exhibits a surprisingly large
Davydov splitting in its absorbance spectrum that produces a visible
color change of the solution from cyan to violet and gives clear evidence
of coherent exciton delocalization
DNA-Controlled Excitonic Switches
Fluorescence resonance energy transfer (FRET) is a promising
means
of enabling information processing in nanoscale devices, but dynamic
control over exciton pathways is required. Here, we demonstrate the
operation of two complementary switches consisting of diffusive FRET
transmission lines in which exciton flow is controlled by DNA. Repeatable
switching is accomplished by the removal or addition of fluorophores
through toehold-mediated strand invasion. In principle, these switches
can be networked to implement any Boolean function
DNA-Templated Aggregates of Strongly Coupled Cyanine Dyes: Nonradiative Decay Governs Exciton Lifetimes
Molecular excitons are used in a variety of applications including light harvesting, optoelectronics, and nanoscale computing. Controlled aggregation via covalent attachment of dyes to DNA templates is a promising aggregate assembly technique that enables the design of extended dye networks. However, there are few studies of exciton dynamics in DNA-templated dye aggregates. We report time-resolved excited-state dynamics measurements of two cyanine-based dye aggregates, a J-like dimer and an H-like tetramer, formed through DNA-templating of covalently attached dyes. Time-resolved fluorescence and transient absorption indicate that nonradiative decay, in the form of internal conversion, dominates the aggregate ground state recovery dynamics, with singlet exciton lifetimes on the order of tens of picoseconds for the aggregates versus nanoseconds for the monomer. These results highlight the importance of circumventing nonradiative decay pathways in the future design of DNA-templated dye aggregates