Synthesis And Recognition Properties Of Rhodamin Derivative Based Metal Ion Probes

Recently, the development of new artificial chemosensors for the recognition ofphysiologically and environmentally important analytes has attracted considerable attention.Among the various detection methods available, UV–vis and fluorescence spectroscopy stillremain the most frequently used modes due to their high sensitivity and easy operational use.Rhodamines are an important class of fluorogenic and chromogenic probes, which are the idealplatforms for development of chemosensors for specific heavy and transition metal ions. Theyhave excellent spectroscopic properties such as long-wavelength emission, high fluorescencequantum yield, and large molar extinction coefficient. The spirolactam form is basically colorless,while the metal induced ring-opened amide form gives rise to strong absorption within thevisible range, this feature provides a vital path way for colorimetric detection of metal ions. wedesigned and synthesized ssome new rhodamine B baed chemosensors, for colorimetric andfluorogenic recognition of Cu²⁺、Hg²⁺and Fe³⁺.The details are as follows:1. A new rhodamine-based sensor Rh1was designed and synthesized by incorporatingrhodamine B and benzimidazole moiety. Sensor Rh1exhibits high selectivity and sensitivity toCu²⁺in CH3CN-water solution （HEPES buffer, pH=7.0） with an obvious color change fromcolorless to pink. Other metal ions such as Hg²⁺, Ag⁺, Pb²⁺, Sr²⁺, Ba²⁺, Cd²⁺, Ni²⁺, Co²⁺, Fe²⁺,Mn²⁺, Zn²⁺, Ce3+, Mg2+, K+and Na+had no such color change and have no significant influenceon Cu²⁺recognition process. The interaction of Cu²⁺and sensor Rh1was proven to adopt a1:1binding stoichiometry and the recognition process is reversible.2. The first novel rhodamine B based sensor, rhodamine B hydrazide methyl5-formyl-1H-pyrrole-2-carboxylate Schiff base Rh2capable of detecting both Cu²⁺and Hg²⁺using two different detection modes has been designed and synthesized. The metal ion inducedoptical changes of Rh2were investigated in MeOH:H2O （3:1） HEPES buffered solution at pH7.4. Sensor2exhibits selective colorimetric recognition of Cu²⁺and fluorogenic recognition ofHg²⁺with UV–vis and fluorescence spectroscopy, respectively. Moreover, both of the Cu²⁺andHg²⁺recognition processes are proven to be hardly influenced by other coexisting metal ions.3. A new rhodamine B-coumarin conjugate Rh3capable of recognize both Cu²⁺and Fe³⁺using two different detection modes have been designed and synthesized. The metal ion inducedoptical changes of Rh3were investigated in CH3CN-H2O （1:1, v/v, HEPES50mM, pH=7.0）solution. Sensor Rh3exhibits selective colorimetric recognition of Cu²⁺and fluorescent recognition of Fe³⁺with UV-vis and fluorescence spectroscopy, respectively. Moreover, both ofthe Cu²⁺and Fe³⁺recognition processes are proven to be barely interfered by other coexistingmetal ions.