# Aggregation, Photoluminescence, and Cytotoxicity of Pt(II) and Re(I) Complexes Bearing Multimodal‐Coordinating Luminophores

## TL;DR

This paper explores how different coordination modes of a ligand affect the properties of Pt(II) and Re(I) complexes, including their light emission and toxicity.

## Contribution

The study introduces a polydentate ligand that enables multiple coordination modes, leading to tunable photoluminescence and cytotoxicity in metal complexes.

## Key findings

- Pt(II) complexes with N*N coordination show tunable emission and cytotoxicity.
- C^N*N coordination in Pt(II) complexes increases photoluminescence quantum yield when co-ligands are exchanged.
- Re(I) complexes using N*N coordination are non-cytotoxic and emit from a 3MLCT state.

## Abstract

In this study, a polydentate ligand capable of adopting multiple coordination modes (N*N, C^N*N, and C^N*N^C) was established. Depending on the chelation conditions and the co‐ligand used in the subsequent steps, nine complexes became accessible. The four Pt(II)‐based species with N*N‐coordination motif show tunable emission and cytotoxicity. Two Pt(II) complexes with C^N*N‐type coordination were also obtained, and the exchange of the co‐ligand from chlorido to cyanido led to an enhancement in the photoluminescence quantum yield from <0.02 to 0.55. These compounds exhibit distinct solid‐state characteristics associated with Pt⋯Pt‐interactions. Interestingly, the tetradentate C^N*N^C‐coordination mode was not accessible, most likely due to kinetic reasons and insolubility‐related purification hurdles. However, the use of a N*N‐coordination mode for a Re(I) center yielded non‐cytotoxic 3MLCT‐state emitters. The multifaceted coordination modes available with the luminophoric ligand enable the design and realization of diverse metal complexes with tailored cytotoxicity and tendency towards intermolecular coupling, both in solution and in crystalline phases.

A polydentate ligand with multiple coordination patterns (bidentate N*N‐mode for Pt(II) and Re(I) centers, tridentate C^N*N‐motive for Pt(II)‐based complexes) is herein presented. The attained coordination‐chemical versatility in combination with different co‐ligands was employed to achieve sophisticated structural features and tunable photophysical properties, including aggregation and cytotoxicity.