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Solvent Induced Helix Folding of Defined Indolenine Squaraine Oligomers.

ABSTRACT: A protecting group strategy was employed to synthesise a series of indolenine squaraine dye oligomers up to the nonamer. The longer oligomers show a distinct solvent dependence of the absorption spectra, that is, either a strong blue shift or a strong red shift of the lowest energy bands in the near infrared spectral region. This behaviour is explained by exciton coupling theory as being due to H- or J-type coupling of transition moments. The H-type coupling is a consequence of a helix folding in solvents with a small Hansen dispersity index. DOSY NMR, small angle neutron scattering (SANS), quantum chemical and force field calculations agree upon a helix structure with an unusually large pitch and open voids that are filled with solvent molecules, thereby forming a kind of clathrate. The thermodynamic parameters of the folding process were determined by temperature dependent optical absorption spectra.

SUBMITTER: Turkin A

PROVIDER: S-EPMC8251825 | biostudies-literature | 2021 Jun

REPOSITORIES: biostudies-literature

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Solvent Induced Helix Folding of Defined Indolenine Squaraine Oligomers.

Turkin Arthur A Holzapfel Marco M Agarwal Mohit M Fischermeier David D Mitric Roland R Schweins Ralf R Gröhn Franziska F Lambert Christoph C

Chemistry (Weinheim an der Bergstrasse, Germany) 20210507 32

A protecting group strategy was employed to synthesise a series of indolenine squaraine dye oligomers up to the nonamer. The longer oligomers show a distinct solvent dependence of the absorption spectra, that is, either a strong blue shift or a strong red shift of the lowest energy bands in the near infrared spectral region. This behaviour is explained by exciton coupling theory as being due to H- or J-type coupling of transition moments. The H-type coupling is a consequence of a helix folding i ...[more]

PMID: 33871113

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Project description: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.

Dataset Information

Solvent Induced Helix Folding of Defined Indolenine Squaraine Oligomers.

Publications

Solvent Induced Helix Folding of Defined Indolenine Squaraine Oligomers.

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