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 (3MMLCT) 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CC6H4(CH2NMe3‐4)}]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 3MMLCT 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 3MMLCT emission in the PPE‐SO3−–1 ensemble.