Multiple fluorescent behaviors of phenothiazine-based organic molecules

•We synthesized and investigated the optical diversities of Di-aryl-substituted phenothiazine.•Molecule aggregated to form FON under the acidic aqueous condition.•Red emission fluorescence occurred in alkaline DMSO solution.•It is conventional to manufacture a stable NIR dye with oxidation by iodine.•Photodamage to cancer cells was observed with low dark-toxicity.

We have designed a conventional one-step Suzuki coupling synthetic method to prepare 3,7-di-aryl substituted 10H-phenothiazine derivatives and investigated their optical behaviors. The compound 3,7-Bis (4-aminophenyl) phenothiazine (compound 1), substituting with electron-donating aniline, can exhibit photodamage behavior toward cancer cells. Furthermore, the compound 1 can form fluorescent organic nanoparticle (FON) in acidic aqueous whereas can emit red fluorescence in alkaline organic solvent. More importantly, compound 1 can be oxidized to manufactured a stable near-IR dye (>950 nm). Alternatively, the control compound 3,7-Bis (4-nitrophenyl) phenothiazine (compound 2) enabled us to determine that an electron-withdrawing group, when attaching on the phenothiazine, is unfavorable for molecular design to manufacture a cation form of NIR dye but is favorable to stabilize the phenothiazinate core and manufacture an anion form of NIR dye.

Graphical abstractThis manuscript reports a convenient method to prepare novel aryl-substituted phenothiazine derivatives with special optical distinguishing features: (1) formation of FON; (2) red emission fluorescence; (3) NIR dye; (4) photodamage to cancer cells.Figure optionsDownload full-size imageDownload as PowerPoint slide