Modulate the structures and photophysical properties of pyrene-based far-red fluorescent cationic dyes by regio-effect.

Graphical abstract Highlights • Comparison study on 5 regioisomeric pyrene dyes indicate the regio-effect with an order of 1-pyrenyl > 4-pyrenyl > 2-pyrenyl. • 4-Substituted isomer demonstrated exceptionally large Stokes shift and high fluorescence quantum yield. • Preliminary fluorescent cell imaging indicated these pyrene cationic dyes could be active mitochondrial probes. Abstract Two series of regioisomeric mono-substituted far-red fluorescent pyrene-indolium and pyrene-pyridinium conjugated dyes were synthesized, and their structures were ambiguously determined by single crystal X-ray diffractions. The photophysical properties of these pyrene-containing dyes in several solvents were investigated to figure out the modulation by changing the site of substituent on the pyrene moiety. The 4-substituted pyrene dyes Py-4 and PP-4 exceptionally demonstrated remarkable fluorescence quantum yield and much larger Stokes shift than their regioisomers (Δ ṽ of PP-4 is 7732 cm−1 in acetonitrile). Preliminary cell staining and fluorescent imaging experiments indicated that <bold> t -Bu-Py-4</bold> could be used as mitochondrial probe with good selectivity and low cytotoxicity. [ABSTRACT FROM AUTHOR]