Rhodamine appended terphenyl: A reversible “off–on” fluorescent chemosensor for mercury ions

A new terphenyl derivative 3 bearing rhodamine as a fluorophore was designed and synthesized as a selective fluorescent and colorimetric sensor for Hg2+ ions. Highly selective and sensitive “off–on” type fluorescent changes were observed upon the addition of Hg2+ ions. Selective fluorescent enhancement of receptor 3 was attributed to ring opening from the spirocyclic form (non-fluorescent) to ring-opened amide form (fluorescent).