Dimensional regulation of the aggregation-induced emission properties for complexes

Abstract

Aggregation-induced emission (AIE) is a fascinating luminescence phenomenon that provides new ideas for developing new fluorescent devices. However, research on photofunctional complexes with AIE properties is still in its infancy, mainly because the motion of the AIE molecules that can move freely will be greatly restricted after immobilization in the complex. Therefore, extending the AIE properties of organic molecules to their constructed complexes has been difficult. To explore a simple and efficient way to introduce the AIE properties of organic molecules into complexes, two similar tetraphenyl ethylene (TPE) carboxylic acid derivatives: tpemc and tpedc with different coordination sites were used to design and construct a series of Eu-complexes with three different dimensions in this work, namely, complex 1 ({[Eu₂(tpedc)₃(DMA)(H₂O)₂]·3DMA·2H₂O}_n, two-dimensional), complex 2 ([Eu(tpemc)₂(DMA)(AcO)]_n, one-dimensional), and complex 3 ([Eu(tpemc)₃(phen)(DMA)(H₂O)]·H₂O, zero-dimensional). Complexes 1–3 showed an incremental AIE phenomenon, which indicated that the restriction of the AIE groups in low-dimensional complexes was limited. They still exhibited a certain movement space; viscosity response experiments and the analysis of a single crystal model with variable temperature also confirmed this result. Therefore, the construction of similar low-dimensional complexes could be regarded as a simple and effective method to introduce AIE properties. In addition, we found that both complexes 2 and 3 exhibited characteristic emissions of Eu³⁺ at low temperatures, and we explored this particular phenomenon in detail through time-dependent density functional theory (TD-DFT) calculations and energy level analysis. Moreover, they also have potential applications in temperature sensing and cell bioimaging.