Mitochondria-targeted F16 derivatives: a new synthetic approach and photoactive properties

New F16 derivatives – ( E )-4-(1 H -indol-3-ylvinyl)- N -alkylpyridinium salts containing phenyl substituents on the pyridine ring were prepared by the reaction of ( E )-4-(1-(1-methyl-1 H -indol-3-yl)prop-1-en-2-yl)-2,6-diphenylpyrylium perchlorate with amines. The use of pyrylium salts as starting compounds is an advantage over traditional F16 syntheses, based on the reactions of pre-synthesized pyridines, since it allows the introduction of any aromatic and/or aliphatic substituents into the pyridine ring. The obtained compounds exhibit properties of dual-state emission (DSE). The extremely low fluorescence quantum yields in solution (ϕ f ≤ 0.004) significantly limit their practical applications. However, the substantially higher quantum yields observed in the solid state (ϕ f = 0.023–0.045) suggest their potential utility for imaging in aggregated or membrane-bound systems. Photoinitiated processes in F16 derivatives, along with the fluorescence of the original E -isomeric forms, include photochromism, which allows them to be considered as fluorescent molecular switches. The optical properties of one of the compounds allow it to be used to assess membrane potential in isolated mitochondria and observe its accumulation in mitochondria of living cells by fluorescent microscopy. A comparison of the penetration of the lipophilic cations, both those obtained in this study and known in the literature, through an artificial lipid bilayer membrane in response to the application of a transmembrane electrical potential is carried out.