Rhodamine urea derivatives as fluorescent chemosensors for Hg2+

New rhodamine derivatives bearing urea group have been synthesized for the detection of metal ions. Especially, the dimeric system 2 displayed a selective fluorescent enhancement and colorimetric change upon the addition of Hg2+, in which the spirolactam (nonfluorescent) to ring opened amide (fluorescent) process was utilized. The association constant of 2 with Hg2+ was calculated as 3.2 × 105 M−1.