Fig. 2

Properties of 2-hydroxymethyl (HM) rhodamines. a Structures of rhodamine derivatives. b pH-dependency of absorbance of each probe (1 μM) in 100 mM NaPi buffer. Detection wavelengths were 550 nm for 2-HM OR, 585 nm for 2-HM SeR, 650 nm for 2-HM SiR, and 635 nm for 2-HM GeR