Cyanine dye molecular aggregates have significant potential for applications such as shortwave infrared (SWIR, 1000–2000 nm) imaging, phototonics and telecommunications, due to the wide tunability of this large family of chromophores. However, a lack of understanding about the direct relationship between the self-assembly mechanism and photophysical properties make it challenging to effectively design molecular aggregates for specific applications. In the self-assembly process, monomer dyes are dissolved in methanol and combined with water and salt (optional) to induce the formation of one or more aggregates, which can be classified as H-, I-, or J-aggregates. H-aggregates are those which incur a blueshift in absorption spectra when compared to the monomer dye, while I- and J-aggregates incur a redshift. I-aggregate refers to any redshifted aggregate whose bright state does not lie at the band-edge, while the term J-aggregate is reserved for those whose bright state is at the band-edge. Previous work has established a systematic process for screening aggregation by modifying three parameters during the self-assembly process: monomer concentration, solvent to cosolvent ratio, and salt concentration. Here, we demonstrate that by tuning monomer structures and solvation conditions, a single monomer can self-assemble to form several aggregates with distinct spectral features and different morphologies. These distinct species can be selected for by minor modifications to the self-assembly conditions. For example, changing the solvent to cosolvent ratio by only 5% volume, can produce aggregates with distinct absorption spectra and morphologies. Additionally, small modifications to the structure of the dye monomer, such as the addition of a single carbon atom, have also been shown to dramatically affect the aggregates formed. The cyanine dyes discussed here demonstrate that a thorough investigation of self-assembly conditions is needed to uncover all potential aggregates that a single dye monomer can form.

Tuning morphology and photophysics of cyanine dye molecular aggregates via solvation

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.