Induced Self-Assembly and Disassembly of Alkynylplatinum(II) 2,6-Bis(benzimidazol-2′-yl)pyridine Complexes with Charge Reversal Properties: “Proof-of-Principle” Demonstration of Ratiometric Förster Resonance Energy Transfer Sensing of pH

Abstract

A series of pH-responsive alkynylplatinum(II) 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) complexes with charge-reversal properties was synthesized, and the supramolecular assemblies between conjugated polyelectrolyte, PFP-OSO 3 − , and [Pt{bzimpy(TEG) 2 }{C�C−C 6 H 3 −(COOH) 2 -3,5}]Cl (1) have been studied using UV−vis absorption, emission, and resonance light scattering (RLS) spectroscopy. An efficient Forster resonance energy transfer (FRET) from PFP-OSO 3 − donor to the aggregated 1 as acceptor with the aid of Pt(II)•••Pt(II) interactions has been presented, which leads to a growth of triplet metal−metal-toligand charge transfer ( 3 MMLCT) emission in the low-energy red region. The twocomponent PFP-OSO 3 − −1 ensemble was then exploited as a "proof-of-principle" concept strategy for pH sensing by tracking the ratiometric emission changes. With the aid of judicious molecular design on the pH-driven charge-reversal property, the polyelectrolyte-induced self-assembly and the FRET from PFP-OSO 3 − to the platinum(II) aggregates have been modulated. Together with its excellent reversibility and photostability, the extra stability provided by the Pt(II)•••Pt(II) and π−π stacking interactions on top of the electrostatic and hydrophobic interactions existing in polyelectrolye−complex assemblies has led to a selective and sensitive pH sensing assay.

Luminescent alkynylplatinum(II) terpyridine-containing conjugated polymers: synthesis, characterization and photophysical studies

“…Unlike most other commonly studied transition metal centers, including ruthenium(II), rhodium(III) and iridium(III), d 8 platinum(II) center favors coordination of a square-planar geometry, and their complexes, especially those bearing conjugated aromatic ligands capable of exhibiting π-π interactions, are well-known for their ability to self-assemble [22][23][24][25][26] , forming aggregates [27][28][29][30][31] and providing remarkable photophysical properties associated with Pt•••Pt and π-π interactions [32][33][34][35] . In light of their supramolecular assembly capability, it is envisaged that the introduction of platinum centers into conjugated polymers may provide an opportunity to further modulate the photophysical and morphological properties of the resulting metal-organic hybrid materials [36][37][38] . Although there were examples of platinum(II)-containing conjugated polymers such as platinum(II) polyynes [39][40][41][42][43][44][45][46] and cyclometalating bidentate ligand-containing platinum(II)-based conjugated polymers [47][48][49] , none of these examples demonstrates supramolecular assembly properties or utilizes the system of tridentate N-donor ligands.…”

Editorial for Forum on Applied Supramolecular Materials

“…The modulation of energy transfer processes in this system helped in efficient photoinduced ROS generation, which was exploited for type II photo-oxidation reactions. Yam et al designed and developed a series of pH-responsive alkynylplatinum­(II)-2,6-bis­(benzimidazole-2′-yl)­pyridine supramolecular complexes with charge-reversal properties . Further supramolecular assemblies were prepared with one such Pt complex and conjugate polyelectrolyte where efficient Förster resonance energy transfer (FRET) was observed from the PFP-OSO 3– donor to the aggregated Pt complex supported by Pt­(II)···Pt­(II) interactions.…”

“…Yam et al designed and developed a series of pH-responsive alkynylplatinum(II)-2,6-bis(benzimidazole-2′-yl)pyridine supramolecular complexes with charge-reversal properties. 14 Further supramolecular assemblies were prepared with one such Pt complex and conjugate polyelectrolyte where efficient Forster resonance energy transfer (FRET) was observed from the PFP-OSO 3− donor to the aggregated Pt complex supported by Pt(II)•••Pt(II) interactions. This ultimately led to a growth of triplet metal−metal-to-ligand charge transfer ( 3 MMLCT) emission in the low-energy region.…”