Hydrophilization of hydrophobic azulene derivative by substitution with polyallylamine without drastically changing its optical properties

Azulene is promising for application as a fluorescent probe in bioimaging because of its optical functions. For biological applications, hydrophilization of hydrophobic azulene derivatives is a hot topic of research; however, such hydrophilization has not been achieved without drastically changing the optical functions. In this study, we focused on 7-isopropyl-4-methylazulene-1-carboxylic acid as a representative hydrophobic azulene derivative and condensed it with highly hydrophilic poly(allylamine) to produce guaiazulene-substituted poly(allylamine). The polymer with 7% introduction was water-soluble, this being the first reported synthesis of a water-soluble azulene derivative-substituted polymer. The absorption spectrum of the polymer is almost identical to that of 7-isopropyl-4-methylazulene-1-carboxylic acid.

Scheme of hydrophilization of hydrophobic azulene derivative by substitution with poly(allylamine) and figures of optical properties of azulene derivative and azulene-derivative polymer.