Cd(II)-triggered excimer–monomer conversion of a pyrene derivative: time dependent red-shift of monomer emission with cell staining application† Animesh Sahana, a Arnab Banerjee, a Sisir Lohar, a Subarna Guha, a Sudipta Das, a Subhra Kanti Mukhopadhyay b and Debasis Das * a Received 2nd June 2012, Accepted 5th July 2012 DOI: 10.1039/c2an35731c An efficient fluorescent probe (E)-N1-((E)-2-((pyren-7-yl)methyl- eneamino)ethyl)-N2-((pyren-7-yl)methylene)ethane-1,2-diamine (L) has been synthesized by a facile one-step condensation reaction. L can selectively detect Cd 2+ in presence of other common metal ions in 0.1 M HEPES buffered DMSO–water (4 : 1, v/v) medium. The detection limit of Cd 2+ is 1.8  10 8 M. Cd 2+ can effectively convert the excimer emission of L into its monomer emission which in turn exhibits a time-dependent red-shift. Cadmium ranks seventh on the top 20 Hazardous Substances Priority List by the Agency for Toxic Substances and Disease Registry and US Environmental Protection Agency (EPA). 1 Exten- sive use of Cd in Ni–Cd batteries, phosphate fertilizers, pigments, and semiconducting quantum dots/rods 2 has exposed and caused severe harmful effects to human health like renal dysfunction, calcium metabolism disorders, reduced lung capacity, an increased incidence of certain forms of cancer and serious health disorders. 3 With Cd being a highly toxic heavy metal, the WHO and the US EPA 1,4 has set its maximum tolerance limit in bottled water as 4 nM and 40 nM respectively. In the past few years, various methods have been developed for determination of Cd 2+ . Among them the fluorescence sensing method has become the most important. The fluorescence method is widely used due to its simplicity, high selectivity, high sensitivity, and lower detection limit, ease of operation, high quantum yield and useful applications in environmental chemistry, medicine and biology. 5 The design of fluorescent probes is generally based on intra- molecular charge transfer (ICT), 6 photoinduced electron transfer (PET), 7 chelation enhanced fluorescence (CHEF), 8 metal–ligand charge transfer (MLCT), 9 excimer/exciplex formation, 10 imine isom- erization, 11 intermolecular hydrogen bonding, 12 excited-state intra- molecular proton transfer, 13 displacement approach, 14 fluorescence resonance energy transfer, 15 etc. Generally a chemical sensor includes two components, a reporter unit called fluorophore, and an ionophore, which can be either covalently linked in one molecule or an independent species, and additionally a mechanism for communication between them. 16 When the target analyte binds to the recognition center, changes occur in its optical properties (e.g., enhancement or quenching of absorption or fluorescence) of the chemosensor. The pyrene (Py) moiety is one of the most useful fluorophores due to its efficiency in excimer forma- tion and subsequent changes in its emission properties. 17 A fluores- cent chemosensor containing more than one pyrenyl group may exhibit excimer emission by two different mechanisms. One results from p–p stacking of the pyrene rings from two different molecules resulting in a characteristic decrease of the excimer emission intensity with a concomitant increase of monomer emission intensity. The other mechanism is based on the interaction of an excited pyrene (Py*) unit with a ground state pyrene (Py) unit. 18 Till date, only a few Cd 2+ -selective fluorescence sensors have been reported, 19 while Cd(II)- triggered excimer–monomer conversion of a pyrene derivative is being reported for the first time. We have developed a novel Cd(II)-selective fluorescent probe (E)- N1-((E)-2-((pyren-7-yl)methyleneamino)ethyl)-N2-((pyren-7-yl)meth- ylene)ethane-1,2-diamine (L). In the presence of Cd(II), L undergoes an excimer to monomer conversion and subsequently a significant red shift of monomer emission is observed in HEPES buffer (0.1 M) at pH 7.4 (DMSO : water ¼ 4 : 1, v/v). Among other common metal ions, only Zn 2+ shows a little fluorescence enhancement. Scheme 1 shows the facile one-step synthesis of L. The molecular structure and purity of L has been examined from different spec- troscopic studies like 1 H NMR, ESI-MS, and FTIR. It was well known that the performance of fluorescence sensors based on an Scheme 1 Synthesis of L. Reagents and conditions: (i) reflux for 10 h in ethanol. a Department of Chemistry, The University of Burdwan, Burdwan 713104, India b Department of Microbiology, The University of Burdwan, Burdwan 713104, India † Electronic supplementary information (ESI) available. See DOI: 10.1039/c2an35731c 3910 | Analyst, 2012, 137, 3910–3913 This journal is ª The Royal Society of Chemistry 2012 Dynamic Article Links C < Analyst Cite this: Analyst, 2012, 137, 3910 www.rsc.org/analyst COMMUNICATION Downloaded by University of Burdwan on 20 January 2013 Published on 06 July 2012 on http://pubs.rsc.org | doi:10.1039/C2AN35731C View Article Online / Journal Homepage / Table of Contents for this issue