Coordination-Enhanced Luminescence on Tetra-Phenylethylene-Based Supramolecular Assemblies.

Qian-Qian Yan,Qing-Fu Sun,Li-Peng Zhou,Ting Zhang,Guang-Lu Zhang,Shao-Jun Hu

doi:10.3390/molecules23020363

Abstract

Materials with aggregation-induced emission (AIE) properties have received increased attention recently due to their potential applications in light-emitting devices, chemo/biosensors and biomedical diagnostics. In general, AIE requires the forced aggregation of the AIEgens induced by the poor solvent or close arrangement of AIEgens covalently attached to polymer chains. Here, we report two coordination-enhanced fluorescent supramolecular complexes featuring hierarchically restricted intramolecular motions via the self-assembly of tetraphenylethylene (TPE)-based tetra-dentate (La) and bidentate (Lb) ligands and the cis-Pd(en)(NO3)2 (en = ethylenediamine) unit. While the free ligands are non-emissive in dilute solution and show typical AIE properties in both mixed solvent system and the solid state, the self-assembled complexes maintain their fluorescent nature in the solution state. In particular, the Pd4(La)2 complex shows remarkable 6-fold fluorescent enhancement over La in dilute solution. We anticipate that these kinds of coordination-enhanced emissive supramolecules will find applications in biomedical sensing or labeling.

Highlights

Aggregation-caused quenching (ACQ) phenomena of luminescent materials are well known, and hinder many of their applications, such as OLED, chemo- or bio-labeling and sensing
While the free ligands are non-emissive in dilute solution and show typical aggregation-induced emission (AIE) properties in the aggregated states, the self-assembled complexes maintain their fluorescent nature in dilute solution
Such a coordination-enhanced emission behavior has been clearly confirmed by comparison of the two SCCS featuring hierarchically restricted intramolecular motions

Summary

Introduction

Aggregation-caused quenching (ACQ) phenomena of luminescent materials are well known, and hinder many of their applications, such as OLED, chemo- or bio-labeling and sensing. We report the coordination-driven self-assembly and the luminescent studies of two SCCs (1, 2) from the TPE-based polypyridine ligands (La and Lb ) and the (en)Pd(NO3 ) (en = ethylenediamine) clipping units (Scheme 1). While the free ligands are non-emissive in dilute solution and show typical AIE properties in the aggregated states, the self-assembled complexes maintain their fluorescent nature in dilute solution. Such a coordination-enhanced emission behavior has been clearly confirmed by comparison of the two SCCS featuring hierarchically restricted intramolecular motions. Coordination-driven self-assembly of supramolecular complexes 1 and 2 from two TPE-based ligands La,b and the cis-blocked (en)Pd(NO3 ) clips

Results and Discussion

General

Synthesis of Ligand La

Synthesis of Assembly 1

Synthesis of Ligand Lb and Assembly 2

Conclusions