Exciton Delocalization in Indolenine Squaraine Aggregates Templated by DNA Holliday Junction Scaffolds
Exciton delocalization plays a prominent role in the photophysics of molecular aggregates, ultimately governing their particular function or application. Deoxyribonucleic acid (DNA) is a compelling scaffold in which to template molecular aggregates and promote exciton delocalization. As individual d...
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Published in | The journal of physical chemistry. B Vol. 124; no. 43; pp. 9636 - 9647 |
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Main Authors | , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
29.10.2020
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Subjects | |
Online Access | Get full text |
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Summary: | Exciton delocalization plays a prominent role in the photophysics of molecular aggregates, ultimately governing their particular function or application. Deoxyribonucleic acid (DNA) is a compelling scaffold in which to template molecular aggregates and promote exciton delocalization. As individual dye molecules are the basis of exciton delocalization in molecular aggregates, their judicious selection is important. Motivated by their excellent photostability and spectral properties, here, we examine the ability of squaraine dyes to undergo exciton delocalization when aggregated via a DNA Holliday junction (HJ) template. A commercially available indolenine squaraine dye was chosen for the study given its strong structural resemblance to Cy5, a commercially available cyanine dye previously shown to undergo exciton delocalization in DNA HJs. Three types of DNA–dye aggregate configurationstransverse dimer, adjacent dimer, and tetramerwere investigated. Signatures of exciton delocalization were observed in all squaraine–DNA aggregates. Specifically, strong blue shift and Davydov splitting were observed in steady-state absorption spectroscopy and exciton-induced features were evident in circular dichroism (CD) spectroscopy. Strongly suppressed fluorescence emission provided additional, indirect evidence for exciton delocalization in the DNA-templated squaraine dye aggregates. To quantitatively evaluate and directly compare the excitonic Coulombic coupling responsible for exciton delocalization, the strength of excitonic hopping interactions between the dyes was obtained by simultaneously fitting the experimental steady-state absorption and CD spectra via a Holstein-like Hamiltonian, in which, following the theoretical approach of Kühn, Renger, and May, the dominant vibrational mode is explicitly considered. The excitonic hopping strength within indolenine squaraines was found to be comparable to that of the analogous Cy5 DNA-templated aggregate. The squaraine aggregates adopted primarily an H-type (dyes oriented parallel to each other) spatial arrangement. Extracted geometric details of the dye mutual orientation in the aggregates enabled a close comparison of aggregate configurations and the elucidation of the influence of dye angular relationship on excitonic hopping interactions in squaraine aggregates. These results encourage the application of squaraine-based aggregates in next-generation systems driven by molecular excitons. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Idaho State Board of Education USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division National Institutes of Health (NIH) MJ Murdock Charitable Trust SC0020089; 1648655; P20GM103408; P20GM109095; 0619793; 0923535 National Science Foundation (NSF) National Institute of General Medical Sciences (NIGMS) |
ISSN: | 1520-6106 1520-5207 |
DOI: | 10.1021/acs.jpcb.0c06480 |