A Six‐Armed Phenhomazine Ligand with a Potential “Turn‐Off” Copper(II) Sensing Capability through Terbium(III) Luminescence Quenching

Abstract

Herein, the design, synthesis, and characterization of ap henhomazine ligand are described. The ligand has six pendant acetate arms designed for the combined coordination of copper(II) and lanthanide(III) ions, with the perspective of developing a" turn-off"c oppers ensor. The key step for the ligand preparation was the one-step endomethylene bridge fission of ad iamino Trçger's base with ac oncomitant alkylation. Fluorescence anda bsorption spectroscopies as well as nuclearm agnetic resonance (NMR) experiments were performed to analyzea nd understand the coordination properties of the ligand. Transitionm etal coordination was drivenb yt he synergistic effect of the free nitrogen atoms of the diazocinic core and the two central acetate arms attachedt ot hose nitrogen atoms, whereas lanthanide coordinationi sp erformed by the external acetate arms, presumably forming as elf-assembled 2:2m etallosupramolecular structure. The terbiumc omplex shows the typical green emissionw ith narrowb ands andl ong luminescence lifetimes.T he luminescence quenching produced by the presence of copper(II) ions was analyzed.T his work sets, therefore, as tartingp oint fort he development of ap henhomazine-based "turn-off" copper(II) sensor.

Innovative Multipodal Ligands Derived from Tröger's Bases for the Sensitization of Lanthanide(III) Luminescence

“…Compound 6 was alkylated with tert ‐butyl bromoacetate to give the tetra‐ tert ‐butyl ester 8 , which was finally deprotected to produce the tetraacid 2 in a yield of 45 % from diamino‐TB 6 (Scheme 1). [35] This compound was previously prepared by our group in our study of a six‐armed tetrahydrophenhomazine, but its lanthanide coordination properties were not studied [36] …”

“…[23,24] The absorption spectrum of compound 2 resembles those of the parent compound 6 ando ther p-phenylenediamines, showingt hat the endomethylene bridge does not strongly affect the electronic transitions in the dibenzodiazocinic framework and that the p-phenylenediamine structure is the origin of the spectroscopic features. [24,36,44] The redshifted absorption band observed for compound 2 at 310 nm is less intense and energetic than in the case of compound 1,a nd the Stokes shift is substantially smaller for the former, with emission centered at 372 nm.…”

“…[35] This compound was previously prepared by our group in our study of as ix-armed tetrahydrophenhomazine, buti ts lanthanide coordinationp roperties were not studied. [36] Synthesis of ligand families3and 4…”

Two‐step Conformational Control of a Dibenzo Diazacyclooctane Derivative by Stepwise Protonation

“…Such a two-step conformational control of the DACO derivative would to be useful for developing new stimuli-responsive supramolecular systems that exhibit multistep properties change as well as for controlling the properties of DACO-containing polymers [7] and molecules. [12] Studies along this line and are underway in our group.…”