Rational design of ratiometric fluorescent probes for bisulfite and viscosity detection in mitochondria without spectral crosstalk

In this work, by the π-conjugation of triphenylamine and pyridine acetonitrile, a precursor containing a pyrid-3-yl and a triphenylamine functionalised acrylonitrile (TPP) was obtained with a D-π-A structure. By further decorating pyridine moiety with N-methyl and N-benzyl groups, respectively, TPP-Ben and TPP-Me were constructed with positive charges. Interestingly, although TPP, TPP-Ben, and TPP-Me show sensitive responses to viscosity, their optical behavior towards bisulfite is distinctly different. TPP is inert to bisulfite, while TPP-Ben exhibits fluorescence “turn-on” response but shows poor selectivity. Only TPP-Me realized the perfect dual-detection of bisulfite and viscosity with the virtues of fluorescence ratiometry, little spectral crosstalk, a large Stokes shift, and good selectivity. The detection behavior of TPP-Me have been successfully confirmed in mitochondria of HeLa cells. [Display omitted] •Three similar molecular rotators with D-π-A structure were constructed for dual detection.•The relationship between substituents and their sensing performances were carefully compared.•TPP-Me shows a gap of 160 nm between two emission bands, realizing dual detection without spectral cross-interference.•The perfect dual-detection of bisulfite and viscosity were confirmed in mitochondria of HeLa cells.