Influence of the amidine fragment on spectral properties of xanthene dyes

Abstract

We synthesized a series of new xanthene dyes containing dimethylamidine group and investigated the influence of this fragment in the composition of xanthene dyes on their spectral characteristics. The amidine fragment mainly affects the absorption and emission maxima due to the π-conjugation of this substituent with xanthene moiety which leads to red shifts by 41–90 nm in the spectra. The most long-wavelength dye, derivative with 1,3,3-trimethyl-3H-indolium, have an absorption maximum at 661 nm, and an emission at 701 nm in methanol. The addition of a large excess of trifluoroacetic acid to the solution of this dye lead to a hypsochromic shift of absorption maximum to 585 nm, which is associated with the protonation of the amidine substituent. The absorption spectra of the corresponding compounds without amidine fragment after addition of trifluoroacetic acid remain almost identical, which proved the π-conjugation of the amidine fragment, but not only oxygen of xanthene moiety.