New near-infrared rhodamine dyes with large Stokes shifts were developed and applied for sensitive detection of cellular pH changes and fluctuations by incorporating an additional amine group with fused rings.

Formyl groups at 6- and 2,6-positions initiated Knoevenagel reactions of the methyl groups at the 7, and 1,7-positions of 1,3,5,7-tetramethyl BODIPY dyes with aromatic aldehydes. Formation of vinyl bonds at the 7-, and 1,7-positions facilitates further Knoevenagel reactions of the methyl groups at the 3,5-positions. This approach offers fast, facile and versatile ways to prepare potential novel building blocks of BODIPY dyes for conjugated oligomers, dendrimers, and highly water-soluble, near-infrared emissive sensing materials.