Influence of Hydrophobicity on Excitonic Coupling in DNA-Templated Indolenine Squaraine Dye Aggregates

Olga A. Mass, Christopher K. Wilson, German Barcenas, Ewald A. Terpetschnig, Olena M. Obukhova, Olga S. Kolosova, Anatoliy L. Tatarets, Lan Li, Bernard Yurke, William B. Knowlton, Ryan D. Pensack, Jeunghoon Lee

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Abstract

Control over the strength of excitonic coupling in molecular dye aggregates is a substantial factor for the development of technologies such as light harvesting, optoelectronics, and quantum computing. According to the molecular exciton model, the strength of excitonic coupling is inversely proportional to the distance between dyes. Covalent DNA templating was proved to be a versatile tool to control dye spacing on a subnanometer scale. To further expand our ability to control photophysical properties of excitons, here, we investigated the influence of dye hydrophobicity on the strength of excitonic coupling in squaraine aggregates covalently templated by DNA Holliday Junction (DNA HJ). Indolenine squaraines were chosen for their excellent spectral properties, stability, and diversity of chemical modifications. Six squaraines of varying hydrophobicity from highly hydrophobic to highly hydrophilic were assembled in two dimer configurations and a tetramer. In general, the examined squaraines demonstrated a propensity toward face-to-face aggregation behavior observed via steady-state absorption, fluorescence, and circular dichroism spectroscopies. Modeling based on the Kühn-Renger-May approach quantified the strength of excitonic coupling in the squaraine aggregates. The strength of excitonic coupling strongly correlated with squaraine hydrophobic region. Dimer aggregates of dichloroindolenine squaraine were found to exhibit the strongest coupling strength of 132 meV (1065 cm-1). In addition, we identified the sites for dye attachment in the DNA HJ that promote the closest spacing between the dyes in their dimers. The extracted aggregate geometries, and the role of electrostatic and steric effects in squaraine aggregation are also discussed. Taken together, these findings provide a deeper insight into how dye structures influence excitonic coupling in dye aggregates covalently templated via DNA, and guidance in design rules for exciton-based materials and devices.

Original languageAmerican English
Pages (from-to)3475-3488
Number of pages14
JournalJournal of Physical Chemistry C
Volume126
Issue number7
DOIs
StatePublished - 24 Feb 2022

Keywords

  • dyes and pigments
  • genetics
  • hydrophobicity
  • oligomers
  • squaraine

EGS Disciplines

  • Materials Science and Engineering

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