Dual optical responses of phenothiazine derivatives: near-IR chromophore and water-soluble fluorescent organic nanoparticles

Abstract

We have designed a conventional one-step organic coupling synthetic method to prepare a series of 10H-phenothiazine (PTZ) derivative fluorophores and investigated their optical behavior under alkaline conditions. The unexpected proton detachment at N-10 position (10N-H) of these PTZ derivatives provides switching between the visible fluorophore and near infrared (NIR) chromophore. Both anionic forms of compounds PTZ-NH and PTZ-OH exhibit strong red emission in alkali DMSO solutions, whereas only anionic PTZ-OH exhibits the near infrared absorption wavelength at 1010 nm. Moreover, the unexpected green fluorescence is observed due to the formation of fluorescent organic nanoparticles (FONs) when PTZ-OH is dissolved in alkaline aqueous conditions. These results indicate that these compounds have the potential for use in alkaline sensor applications, especially in aqueous solution.