A fluorescent chemosensor for Zn(II). Exciplex formation in solution and the solid state.
The macrocyclic phenanthrolinophane 2,9-[2,5,8-triaza-5-(N-anthracene-9-methylamino)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) NMe(4)Cl H(2)O-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(II) complex, steady-state and time-resolved fluorescence studies were performed in ethanol solution and in the solid state. In solution, intramolecular pi-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 (I(Exc)/I(M)), the activation energy for the exciplex formation (E(a)) and the binding energy of the exciplex (-DeltaH) were determined. The crystal structure of the [ZnLBr](ClO(4)).H(2)O compound was resolved, showing that in the solid state both intra- and inter-molecular pi-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 pi-stacking (full overlap of the pi-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 pi-stacking complexes or to exciplex emission in solution.
Bencini
Andrea
A
Department of Chemistry, University of Florence, via della Lastruccia 3, 50019 Sesto Fiorentino, Florence, Italy.
Berni
Emanuela
E
Bianchi
Antonio
A
Fornasari
Patrizia
P
Giorgi
Claudia
C
Lima
Joao C
JC
Lodeiro
Carlos
C
Melo
Maria J
MJ
de Melo
J Seixas
JS
Parola
Antonio Jorge
AJ
Pina
Fernando
F
Pina
Joao
J
Valtancoli
Barbara
B
D000097:Acetonitriles; D018360:Crystallography, X-Ray; D000431:Ethanol; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D015336:Molecular Probe Techniques; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000032:analysis* / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D013696:Temperature; D014867:Water; D015032:Zinc / Q000032:analysis* / Q000737:chemistry*
D000097:Acetonitriles; D008024:Ligands; D009942:Organometallic Compounds; D012996:Solutions; C511192:bromo(2,9-(2,5,8-triaza-5-(N-anthracene-9-methylamino)ethyl)-(9)-1,10-phenanthrolinophane)zinc(II); D014867:Water; D000431:Ethanol; D015032:Zinc