Conjugated Polyelectrolyte‐Induced Self‐Assembly of Alkynylplatinum(II) 2,6‐Bis(benzimidazol‐2′‐yl)pyridine Complexes

Abstract

Water-soluble cationic alkynylplatinum(II) 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy) complexes have been demonstrated to undergo supramolecular assembly with anionic polyelectrolytes in aqueous buffer solution. Metal-metal-to-ligand charge transfer (MMLCT) absorptions and triplet MMLCT ((3) MMLCT) emissions have been found in UV/Vis absorption and emission spectra of the electrostatic assembly of the complexes with non-conjugated polyelectrolytes, driven by Pt⋅⋅⋅Pt and π-π interactions among the complex molecules. Interestingly, the two-component ensemble formed by [Pt(bzimpy-Et){CCC6 H4 (CH2 NMe3 -4)}]Cl2 (1) with para-linked conjugated polyelectrolyte (CPE), PPE-SO3 (-) , shows significantly different photophysical properties from that of the ensemble formed by 1 with meta-linked CPE, mPPE-Ala. The helical conformation of mPPE-Ala allows the formation of strong mPPE-Ala-1 aggregates with Pt⋅⋅⋅Pt, electrostatic, and π-π interactions, as revealed by the large Stern-Volmer constant at low concentrations of 1. Together with the reasonably large Förster radius, large HOMO-LUMO gap and high triplet state energy of mPPE-Ala to minimize both photo-induced charge transfer (PCT) and Dexter triplet energy back-transfer (TEBT) quenching of the emission of 1, efficient Förster resonance energy transfer (FRET) from mPPE-Ala to aggregated 1 molecules and strong (3) MMLCT emission have been found, while the less strong PPE-SO3 (-) -1 aggregates and probably more efficient PCT and Dexter TEBT quenching would account for the lack of (3) MMLCT emission in the PPE-SO3 (-) -1 ensemble.

Parallel folding topology-selective label-free detection and monitoring of conformational and topological changes of different G-quadruplex DNAs by emission spectral changes via FRET of mPPE-Ala–Pt(ii) complex ensemble

“…More recently, the photophysical properties of two-component ensembles of alkynylplatinum( ii ) complexes with 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) as the tridentate N -donor ligand and CPEs have been studied. 19 Despite the fact that alkynylplatinum( ii ) bzimpy complexes can undergo self-assembly in solutions similar to that of alkynylplatinum( ii ) terpyridine complexes, 19 – 21 the energy levels of the intraligand and the charge transfer excited states of this class of complexes are significantly different from those of the terpyridine counterparts. 20 a In addition to FRET, the photophysical properties of the two-component ensembles were also governed by photo-induced charge transfer and Dexter triplet energy back-transfer, which are related to the HOMO–LUMO energy gaps and the triplet energies of individual components.…”

“…20 a In addition to FRET, the photophysical properties of the two-component ensembles were also governed by photo-induced charge transfer and Dexter triplet energy back-transfer, which are related to the HOMO–LUMO energy gaps and the triplet energies of individual components. 19 Therefore, the circumspect and sagacious design and choice of their chemical structures would allow the fine-tuning of the extent of fluorescence quenching of the CPEs and photo-sensitization of the triplet metal–metal-to-ligand charge transfer ( 3 MMLCT) emission of the platinum( ii ) complexes. On the other hand, CPEs of different conformations have been found to show different binding constants with platinum( ii ) complexes owing to the differences in spatial interactions among the two chemical species.…”

“…On the other hand, CPEs of different conformations have been found to show different binding constants with platinum( ii ) complexes owing to the differences in spatial interactions among the two chemical species. 19 Through the optimization of the photophysical properties and excited state energies, as well as the conformations and supramolecular architectures of the CPEs and alkynylplatinum( ii ) bzimpy complexes, the two-component ensemble of meta -linked m PPE-Ala and [Pt(bzimpy-Et){C CC 6 H 4 (CH 2 NMe 3 -4)}]Cl 2 ( 1 ) ( Scheme 1 ) has been shown to exhibit very efficient FRET and photo-sensitization of the 3 MMLCT emission of the aggregated alkynylplatinum( ii ) bzimpy complexes. 19 Moreover, stronger interactions between the CPE and alkynylplatinum( ii ) bzimpy complexes have been observed, as compared to the reported two-component ensembles between CPEs and the terpyridine counterparts.…”

“… 19 Through the optimization of the photophysical properties and excited state energies, as well as the conformations and supramolecular architectures of the CPEs and alkynylplatinum( ii ) bzimpy complexes, the two-component ensemble of meta -linked m PPE-Ala and [Pt(bzimpy-Et){C CC 6 H 4 (CH 2 NMe 3 -4)}]Cl 2 ( 1 ) ( Scheme 1 ) has been shown to exhibit very efficient FRET and photo-sensitization of the 3 MMLCT emission of the aggregated alkynylplatinum( ii ) bzimpy complexes. 19 Moreover, stronger interactions between the CPE and alkynylplatinum( ii ) bzimpy complexes have been observed, as compared to the reported two-component ensembles between CPEs and the terpyridine counterparts. 10 All these features suggest that the ensemble of m PPE-Ala and 1 would exhibit superior selectivity and sensitivity for label-free detection of target analytes.…”

Médaille Lavoisier: J. Livage / Neue Mitglieder der Academia Europaea Science Award Electrochemistry: B. D. McCloskey / Ernst‐Haage‐Preis: I. Siewert / Einstein‐Stipendium: D. W. Stephan

“…Yam (Universität Hongkong) wurde in dieser Rubrik vorgestellt, als sie Mitglied des Internationalen Beirats der Angewandten Chemie geworden war . Vor kurzem erschien in Chemistry—A European Journal eine Arbeit von ihr über die Selbstorganisation von Alkinylplatin(II)‐Komplexen; zudem verfasste sie ein Editorial für die Angewandte Chemie über die Stellung der anorganischen Chemie . Yam gehört außerdem den Editorial Advisory Boards von ChemistryOpen und ChemPhysChem an.…”