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

Abstract

<jats:p>&lt;div&gt;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.&lt;/div&gt;</jats:p>

Unveiling the Synergy of Coupled Gold Nanoparticles and J-Aggregates in Plexcitonic Systems for Enhanced Photochemical Applications

“…The overall objective of the present work is to study the formation of plexcitonic systems and demonstrate the effect of plexcitonic coupling on the photophysical and photochemical properties of S2275 dye. It is well established that an increase in ionic strength, achieved through the addition of NaCl, induces the self-assembly of S2275 dye molecules into J-aggregates [32,33]. Figure 1a (red spectrum) gives the UV-Vis-NIR response of S2275 dye showing an intense band in the 400-500 nm region.…”