Styrylpyrylium Dyes as Solvent-Sensitive Molecules Displaying Dual Fluorescence

A series of new molecules showing solvent-sensitive UV/Vis spectroscopic properties have been synthesized and characterized. The new compounds share a common 6-styryl-2,4-disubstituted pyrylium architecture, which allows for visible light excitation (at 400-600 nm) leading to two well-resolved fluorescence bands (separated by up to 200 nm). The photophysical characteristics of the emissions depend on the polarity of the medium, being in apolar solvents highly emissive fluorescent (with quantum yields of ca. 0.6) and displaying the longest wavelength emission (at up to 650 nm). On the other hand, the emission in polar solvents is weaker and centered at shorter wavelengths. The probes are highly hydrophobic which allows their selective accumulation in phosphatidylcholine liposomes.