A Ratiometric Luminescent Switch Based on Platinum Complexes Tethered to a Crown‐Ether Scaffold

Abstract

A ratiometric chemosensor for potassium is reported, based on phosphorescent dinuclear cyclometalated Pt(II) complexes featuring a cis-crown ether as the cation-recognition unit. The metal complexes are blue luminescent in a non-aggregated state but become strongly orange emissive when in a close physical proximity, as is the case when the macrocycle is in the folded state. Upon binding of the cation, unfolding occurs, resulting in a pronounced change in the emission properties (e.g. emission wavelength), which can be used for ratiometric sensing applications. The reversibility of the binding was confirmed by competitive titration experiments with unsubstituted 18-crown-6; the system shows supramolecular switching behavior.

Multinuclear PtII Complexes: Why Three is Better Than Two to Enhance Photophysical Properties

“…[22][23][24][25][26][27][28] The changes in the optical properties are directly correlated with the distance between the Pt centers. [6,11,[29][30][31] Thus, the shorter the distance is, the stronger the electronic Pt•••Pt electronic interaction is, and the more bathochromically shiftedt he MMLCT band is. [32][33] However,t he formation of assembled speciesn ot only changes the absorption and emission energy, but also leads often to an enhancement of the emission quantum yields (PLQY) and to an elongationo ft he excited state lifetime, due to ac hange of the nature of the lowest transitiona nd the increasing rigidity of the packed units.…”

Excimer‐Based On‐Off Bis(pyreneamide) Macrocyclic Chemosensors

“… For a similar study based on phosphorescent dinuclear cyclometalated Pt II complexes, see reference . …”

From reactive carbenes to chiral polyether macrocycles in two steps – synthesis and applications made easy?

“…11 Macrocycles 1e and 1f used as reversible ratiometric luminescent switches and scaffolds to study targeted photophysical properties, respectively. 32,33 to ECD transitions cancelling each other. However, upon cation addition and binding, the overall number of conformations decreased and the novel conformationally-constrained geometries favored the inverted ECD signal(s) leading to the observed enhancement ( Fig.…”

“…The cation can be removed from the macrocycle by addition of regular 18-crown-6, making this system a reversible ratiometric luminescent switch. 32 Perylene substituted macrocycles 1f were also used as convenient scaffolds to study targeted photophysical properties, such as symmetry breaking charge separation. The study was performed using stationary and ultrafast electronic spectroscopies combined with molecular dynamics simulations.…”

“…To induce reversibility, regular 18-crown-6 can be added as a cation scavenger (Fig. 12A), 32 and this led to complete recovery of the original ECD or CPL signals of the "naked" derivatives 1. The sequence of cation addition and removal can be repeated over several cycles making the reversible system an effective and rare example of allied +/À ECD and on/off CPL switches (Fig.…”