LAUSR

Polymethine fluorophores have aided in advancing the fields of biological and material sciences, through advantageous photophysical properties. However, the need to maintain a monomeric state can severely limit the processing ability of dyes and is a major hinderance to their functionality. High concentrations of fluorophore can lead to aggregation and reduce advantageous photophysical properties of monomers. Another concern is "crossing the cyanine limit" in which conjugation within the polymethine scaffold is broken, producing the presence of an asymmetric state diminishing its photophysical behavior. Herein, we attempt to overcome these limitations by exploring anion exchange on a cationic flavylium heptamethine scaffold. By increasing the size and hydrophobicity of the anion, we can effectively tune the degree of ion-pairing within the polymethine dye. Interestingly, we found that the effect of ion-pairing on photophysical properties was subtle for the flavylium heptamethine scaffold in comparison to the more commonly used indolenine cyanine dye. Utilizing larger weakly coordinating anions enabled solubility of the flavylium heptamethine fluorophore in non-polar solvents, which could otherwise not be achieved. Even with more subtle effects than classic cyanine dyes, anion exchange on flavylium polymethine dyes holds potential for further manipulation of the properties of these low energy dyes.