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Principles for Self-Assembly of Cyanine Dyes into 2-Dimensional Excitonic Aggregates Across the Visible and Near-Infrared

preprint
submitted on 03.07.2020 and posted on 07.07.2020 by Arundhati Deshmukh, Austin Bailey, Leandra Forte, Xingyu Shen, Niklas Geue, Ellen Sletten, Justin Caram
Cyanine dyes show a remarkable tendency to form non-covalent supramolecular aggregates with diverse morphologies (dimers, sheets, tubes and bundles). Specific molecular arrangements within these H- or J-aggregates dictate the extraordinary photophysical properties, including long-range exciton delocalization, extreme redshifts, and excitonic superradiance. Despite extensive literature on cyanine dye aggregates, design principles that drive the solution self-assembly to a preferred H- or J-aggregated state are unknown. We present a general approach to tune the thermodynamics of self-assembly, selectively stabilizing H- or J-aggregates and thereby achieving supramolecular control over aggregate photophysics. A simple interplay of solvent to non-solvent ratio, ionic strength or dye concentration yields a broad range of conditions that predictably and preferentially stabilize the monomer, H- or J-aggregate species that can be easily monitored using absorption spectroscopy. Diffusion ordered spectroscopy, cryo-electron microscopy and atomic force microscopy together reveal a dynamic equilibrium between monomers, H-aggregated dimers, and extended J-aggregated 2-dimensional monolayers. This structural information informs a three-component equilibrium model that describes the observed concentration dependence of spectral signatures, showing excellent fit with experimental data and yields the Gibb’s free energies of self-assembly for dimerization and 2D aggregate assembly. We further demonstrate the universality of this approach among several sheet forming cyanine dyes including the benzothiazole and benzimidazole families with absorptions spanning visible, near and shortwave infrared wavelengths.

Funding

NSF CHE #190524

Faculty Research Grant (UCLA Academic Senate)

UCLA UCLA Chemistry and Biochemistry Excellence in Research Fellowship and SG Fellowship

CSST

History

Email Address of Submitting Author

arundhatipd@ucla.edu

Institution

UCLA

Country

United States

ORCID For Submitting Author

0000-0002-7901-8814

Declaration of Conflict of Interest

No conflict of interest.

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