A Fluorescent Molecular Switch Driven by the Input Sequence of Metal Cations: An Azamacrocyclic Ligand Containing Bipolar Anthracene Fragments

Abstract

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 (Zn2+ and Cd2+) 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 Zn2+ 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 Zn2+ binding. In contrast, Cd2+ addition does not result in excimer emission because the Cd2+-AN pi complex, formed by donation of a pi electron of the AN fragments to the adjacent Cd2+, suppresses pi-stacking interactions of the AN fragments. The most notable feature is the appearance of excimer emission controlled by the input sequence of metal cations: Zn2+-->Cd2+ sequential addition (each one equivalent) allows excimer emission, whereas the reverse sequence (Cd2+-->Zn2+) does not. In the Zn2+-->Cd2+ sequence, Cd2+ coordination is structurally restricted by the first Zn2+ coordination with the other polyamine bridge, leading to the formation of a weak Cd2+-AN pi complex. In contrast, for the reverse sequence, the first Cd2+ coordination forms a stable Cd2+-AN pi complex, which is not weakened by sequential Zn2+ coordination, resulting in no excimer emission.

The recognition of 1,5-naphthalenedisulfonate by a protonated azamacrocyclic ligand

“…Protonated receptors H 8 L 1 Cl 8 and H 6 L 2 Cl 6 (Scheme 1) were synthesized according to literature methods. 8,10 Both receptors display strong fluorescence at low pH values, as the electron transfer process is prohibited by the protonation of amines, as observed in previous studies. 8,11…”

“…7 In the present paper, we focused our attention on the polyaza macrocyclic ligand L 1 (Scheme 1), which was previously shown as a fluorescent molecular switch driven by the addition sequence of metal cations (Zn 2+ and Cd 2+ ). 8 We noted that L 1 contains two polyamine binding units and two fluorescent anthracene fragments. Upon protonation, L 1 can recognize anions through both energy terms (electrostatic, hydrogen-bonding and anion-p/p-p interactions) and geometrical factors (size matching effect).…”

Copper(II)-directed static excimer formation of an anthracene-based highly selective fluorescent receptor

“…[29][30][31] Anthracene acting as a fluorophore has been utilized effectively since its emission property varies according to its local environment. [32][33][34] Excellent monomer and excimer emission changes occur at remarkably different wavelengths based on the distance between two anthracene moieties. Excimer emissions are characteristically observed with a broad fluorescence band with the maxima at lower energy in comparison to monomer emissions, and this band can be taken into account to examine the molecular recognition process in more detail.…”

Anthracene‐Based Cyclophanes with Selective Fluorescent Responses for TTP and GTP: Insights into Recognition and Sensing Mechanisms

“…Macrocycles 1 – 3 were prepared by the reaction of 9,10‐anthracenedicarboxaldehyde with the corresponding amines in an acetonitrile‐methanol mixture followed by reduction of the produced Schiff base. The preparation methods described earlier for cyclophanes were slightly modified and optimized . Receptors 1 and 2 were synthesized with low yields (ca.…”

“…The preparation methods described earlier for cyclophanes were slightly modified and optimized. [11,[33][34][35] Receptors 1 and 2 were synthesized with low yields (ca. 15 %), while macrocycle 3 could be obtained in a 43 %y ield.…”