One-pot synthesis of a new rhodamine-based dually-responsive pH sensor and its application to bioimaging

A new calorimetric and fluorescent sensor for the highly acidic pH was developed from rhodamine B, 1-(2-aminoethyl)piperazine, and 4-chloro-7-nitro-2,1,3-benzoxadiazole. The sensor could be synthesized in one pot with an 82.5% yield, and for the first time N,N-diisopropylethylamine was found to be crucial for the rhodamine spirolactam formation. The sensor responded to pH rapidly, visibly, reversibly, highly selectively, and sensitively. From pH 7.77 to 2.03, the absorption and fluorescence intensity of the sensor increased by 285 and 50.3 folds, respectively. The pK(a) value based on the fluorescence titration was 2.87. Fluorescent imaging of living cells treated with the sensor in different pH media indicated that the sensor could provide intracellular pH information. (C) 2014 Elsevier Ltd. All rights reserved.