Stepwise Increase of NdIII-Based Phosphorescence by AIE-Active Sensitizer: Broadening the AIPE Family from Transition Metals to Discrete Near-Infrared Lanthanide Complexes**

We designed two near-infrared (NIR) lanthanide complexes [(L)(2)-Nd(NO3)(3)] (L=TPE2-BPY for 1, TPE-BPY for 2) by employing aggregation-induced emission (AIE)-active tetraphenylethylene (TPE) derivatives as sensitizers, which possessed matched energy to Nd-III, prevented competitive deactivation under aggregation, even shifted the excitation window toward 600 nm by twisted intramolecular charge transfer. Furthermore, benefiting from the 4 f electron shielding effect and antenna effect, the enhanced excitation energies of the AIE-active sensitizers by structural rigidification transferred into the inert Nd-III excited state through (LMCT)-L-3, affording the first aggregation-induced phosphorescence enhancement (AIPE)-active discrete NIR-emitting lanthanide complexes. As 1 equipped with more AIE-active TPE than 2, L -> Nd energy transfer efficiency in the former was higher than that in the latter under the same conditions. Consequently, the crystal of 1 exhibited one of the longest lifetimes (9.69 mu s) among Nd-III-based complexes containing C-H bonds.

Automated summary

In this study, two near-infrared lanthanide complexes were designed using AIE-active TPE derivatives as sensitizers, achieving aggregation-induced phosphorescence enhancement. Compound 1 demonstrated higher energy transfer efficiency from L to Nd compared to compound 2, resulting in a longer lifetime.