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A Fluorescent Molecular Switch Driven by the Input Sequence of Metal Cations: An Azamacrocyclic Ligand Containing Bipolar Anthracene Fragments
Author(s) -
Nishimura Go,
Maehara Hajime,
Shiraishi Yasuhiro,
Hirai Takayuki
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700797
Subject(s) - anthracene , fluorescence , sequence (biology) , ligand (biochemistry) , chemistry , metal , photochemistry , organic chemistry , biochemistry , physics , receptor , quantum mechanics
An azamacrocyclic ligand ( L ) containing two anthracene (AN) fragments connected through two triethylenetetramine bridges has been synthesized, in which each of the bridges can coordinate with one metal cation. The effects of pH and metal cations (Zn 2+ and Cd 2+ ) on the emission properties of L were studied in water. Without metal cations, L does not show any emission at basic pH values. The addition of Zn 2+ leads to the production of excimer emission, which is due to a static excimer formed by direct excitation of the intramolecular ground‐state dimer of the bipolar AN fragments that approach each other by Zn 2+ binding. In contrast, Cd 2+ addition does not result in excimer emission because the Cd 2+ –AN π complex, formed by donation of a π electron of the AN fragments to the adjacent Cd 2+ , suppresses π‐stacking interactions of the AN fragments. The most notable feature is the appearance of excimer emission controlled by the input sequence of metal cations: Zn 2+ →Cd 2+ sequential addition (each one equivalent) allows excimer emission, whereas the reverse sequence (Cd 2+ →Zn 2+ ) does not. In the Zn 2+ →Cd 2+ sequence, Cd 2+ coordination is structurally restricted by the first Zn 2+ coordination with the other polyamine bridge, leading to the formation of a weak Cd 2+ –AN π complex. In contrast, for the reverse sequence, the first Cd 2+ coordination forms a stable Cd 2+ –AN π complex, which is not weakened by sequential Zn 2+ coordination, resulting in no excimer emission.