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

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 (Delta(nu) over tilde of PP-4 is 7732 cm(-1) in acetonitrile). Preliminary cell staining and fluorescent imaging experiments indicated that t-Bu-Py-4 could be used as mitochondrial probe with good selectivity and low cytotoxicity.