Systematic study of synthesizing various heteroatom-substituted rhodamines from diaryl ether analogues

The dye rhodamine, as the most popular scaffold to construct fluorescent labels and probes, has been explored extensively on its structure -fluorescence relationships. Particularly, the replacement of the oxygen atom in the 10th position with heteroatoms obtained various new rhodamines with improved photophysical properties, such as brightness, photostability, red-shifted emission and fluorogenicity. However, the applications of heteroatom-substituted rhodamines have been hindered by difficult synthetic routes. Herein, we explored the condensation strategy of diaryl ether analogues and o-tolualdehyde to synthesize various heteroatom-substituted rhodamines. We found that the electron property and steric effect in the rhodamine 10th position de-termined the synthetic yield. It's concluded that this condensation method was more suitable for the synthesis of heteroatom-substituted rhodamines with small or electron-donating groups like rhodamine, S-rhodamine and Si-rhodamine. We hope these results will benefit the design and synthesis of heteroatom-substituted rhodamines. (C) 2020 Published by Elsevier B.V.