Terpy(Pt–salphen)₂ Switchable Luminescent Molecular Tweezers

Abstract

The design and synthesis of switchable molecular tweezers based on a luminescent terpy(Pt-salphen)2 (1; terpy=terpyridine) complex is reported. Upon metal coordination, the tweezers can switch from an open "W"-shaped conformation to a closed "U"-shaped form that is adapted for selective recognition of cations. Closing of the tweezers by metal coordination (M=Zn(2+), Cu(2+), Pb(2+), Fe(2+), Hg(2+)) was monitored by (1)H NMR and/or UV/Vis titrations. During the titration, exclusive formation of the 1:1 complex [M(1)] was observed, without appearance of an intermediate 1:2 complex [M(1)2]. The crystallographic structure of the 1:1 complex was obtained with Pb(2+) and showed a distorted helical structure. Selective intercalation of Hg(2+) cations by the closed "U" form was observed. The tweezers were reopened by selective metal decoordination of the terpyridine ligand by using tris(2-aminoethyl)amine (tren) as a competitive ligand without modification of the Pt-salphen complex. Detailed photophysical studies were performed on the open and closed tweezers. Structured emission was observed in the open form from the Pt-salphen moieties, with a high quantum yield and a long lifetime. The emission is slightly modified upon closing with 1 equivalent of Zn(2+) or Hg(2+), whereas a dramatic quenching was obtained upon intercalation of additional Hg(2+).

Switching Magnetic Properties by a Mechanical Motion

“…Coordination-based switches are attractive as they present benefits over photochemical switches, by enabling total conversion and offering thermal stability. We have recently developed switchable molecular tweezers [65,66], which are based on a terpyridine ligand substituted by metal-salphen complexes that can switch upon metal coordination from a "W" shaped open form to a "U" closed form bringing the two salphen moieties in close spatial proximity ( Figure 15). We have used this modular design to control the magnetic interaction between paramagnetic Cu(II)-salphen (d 9 S = 1/2) complexes via a mechanical motion [67].…”

CrIIIas an alternative to RuIIin metallo-supramolecular chemistry

“…27 Some rare (but remarkable) exceptions arose with (i) the serendipitous crystallization by Winpenny and coworkers of poly-chromium wheels at high temperatures (210°C to 400°C) using thermally resistant ligands [28][29][30] and (ii) the use of preformed chromium complexes working as inert partners for the preparation of hydroxo, 31 oxalato, 32,[33][34][35][36] and cyano bridged architectures. 7,9,37 In this context, post-modifications were recently shown to open novel pathways for the stepwise building of multi-metallic assemblies including inert ruthenium-polypyridine complexes [38][39][40] or platinum-salen derivatives, 41,42 but the manipulation of related Cr III -polypyridine entities remains scarce and elusive. [43][44][45] Moreover, recent demonstration that [Cr(2,2′:6′,2″-terpyridine) 2 ] 3+ (u[Cr(tpy) 2 ] 3+ ) complexes rapidly dissociate under slightly alkaline conditions, 46 a trend which confirms a previous observation reported for [Cr(2,2′-bipyridine) 3 ] 3+ (u[Cr(bpy) 3 ] 3+ ), 47 prevents post-treatment of these complexes for the design of organized polynuclear assemblies.…”

Switchable platinum-based tweezers with Pt–Pt bonding and selective luminescence quenching

“…13 Our system, inspired by the work of Lehn, 12a-f is based on a terpyridine (terpy) ligand substituted in 6 and 6″ positions by two arms bearing molecular recognition moieties (Fig. 1).…”