Fluorescent phenothiazine-triazine donor-acceptor conjugates by facile consecutive nucleophilic displacement – Color tuning by substitution and protochromicity

A series of phenothiazine-triazine chromophores is prepared starting from brominated phenothiazine in a one-pot fashion by twofold nucleophilic substitution on cyanuric chloride. The title compounds show high fluorescence quantum yields in solution and in the solid state spanning a color range from deep blue to red by modulating the acceptor strength of the triazine moiety. Electron deficient substituted triazine chromophores exhibit a strong charge transfer character as shown by solvatochromism studies and small singlet-triplet energy gap making them interesting-candidates for thermally activated delayed fluorescence (TADF). Protonation of an electron rich triazine chromophore resulted in shifted spectral emission and showed in one case the formation of complementary emission colors and white light formation. Thus, by substitution of the triazine spectral emission color can be fine-tuned and specific photophysical properties like TADF and white light emission can be addressed.