Silicon Substitution in Oxazine Dyes Yields Near-Infrared Azasiline Fluorophores That Absorb and Emit beyond 700 nm.

Exchanging the bridging oxygen atom in rhodamine dyes with a dimethylsilyl group red-shifts their excitation and emission spectra, transforming orange fluorescent rhodamines into far-red Si-rhodamines. To study the effect of this substitution in other dye scaffolds, synthetic approaches to incorporate silicon into the bridging position of oxazine dyes were developed. The fluorescence of the compact azasiline dyes ASiFluor710 and ASiFluor730 is red-shifted by 57-83 nm from that of Oxazine 1.