A fluorescent chemosensor for Zn(II). Exciplex formation in solution and the solid state

Andrea Bencini, Emanuela Berni, Antonio Bianchi, Patrizia Fornasari, Claudia Giorgi, João C. Lima, Carlos Lodeiro, Maria J. Melo, J. Seixas De Melo, Antonio Jorge Parola, Fernando Pina, João Pina, Barbara Valtancoli

Research output: Contribution to journalArticle

43 Citations (Scopus)

Abstract

The macrocyclic phenanthrolinophane 2,9-[2,5,8-triaza-5-(N-anthracene-9- methylaraino)ethyl]-[9]-1, 10-phenanthrolinophane (L) bearing a pendant arm containing a coordinating amine and an anthracene group forms stable complexes with Zn(II), Cd(II) and Hg(II) in solution. Stability constants of these complexes were determined in 0.10 mol dm-3 NMe4Cl H 2O-MeCN (1 : 1, v/v) solution at 298.1 ± 0.1 K by means of potentiometric (pH metric) titration. The fluorescence emission properties of these complexes were studied in this solvent. For the Zn(n) complex, steady-state and time-resolved fluorescence studies were performed in ethanol solution and in the solid state. In solution, intramolecular π-stacking interaction between phenanthroline and anthracene in the ground state and exciplex emission in the excited state were observed. From the temperature dependence of the photostationary ratio (IEXC/IM), the activation energy for the exciplex formation (Ea) and the binding energy of the exciplex (-ΔH) were determined. The crystal structure of the [ZnLBr](ClO4)·H2O compound was resolved, showing that in the solid state both intra- and inter-molecular π-stacking interactions are present. Such interactions were also evidenced by UV-vis absorption and emission spectra in the solid state. The absorption spectrum of a thin film of the solid complex is red-shifted compared with the solution spectra, whereas its emission spectrum reveals the unique featureless exciplex band, blue shifted compared with the solution. In conjunction with X-ray data the solid-state data was interpreted as being due to a new exciplex where no π-stacking (full overlap of the π-electron cloud of the two chromophores - anthracene and phenanthroline) is observed. L is a fluorescent chemosensor able to signal Zn(II) in presence of Cd(II) and Hg(II), since the last two metal ions do not give rise either to the formation of π-stacking complexes or to exciplex emission in solution.

Original languageEnglish
Pages (from-to)2180-2187
Number of pages8
JournalDalton Transactions
Issue number14
DOIs
Publication statusPublished - 21 Jul 2004

Keywords

  • Molecules
  • Ligands
  • Stability constants

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