Fluorescent homodimer styrylcyanines: synthesis and spectral-luminescent studies in nucleic acids and protein complexes

A series of homodimer styrylcyanine dyes based on (p-dimethylaminostyryl)pyridinium, (p-dimethylaminostyryl)benzoxazolium, (p-dimethylaminostyryl)benzothiazolium, (p-dimethylaminostyryl)-1,3,3-trimethyl-3H-indolium residues were synthesized. Spectral-luminescent properties of the obtained homodimers in free state and in the presence of nucleic acids and BSA were studied. Homodimer styrylcyanines with the length of linkage group of 2 or more carbon atoms demonstrated a DNA-binding preference. Significant long-wave shifts of fluorescence and emission maxima of dyes with short linkage group could be explained by the interaction between chromophores due to the short distance between them, as it is the case for molecular aggregates. Homodimer dyes based on the (p-dimethylaminostyryl)pyridinium residue having linkage group of 5 or more carbon atoms interact with dsDNA with significant emission increase and could be used as DNA specific fluorescent probes.