Achieving Molecular Fluorescent Conversion from Aggregation-Caused Quenching to Aggregation-Induced Emission by Positional Isomerization.

Xinli Wang,Wei Liu,Renfu Li,Bin Lin,Zexin Wang,Tao Dai,Lijun Xie,Shitao Sun,Jinle Hao,Nannan Chen,Liwei Chen,Zhenli Li,Xiang Lin

doi:10.3390/molecules27010193

Abstract

In this work, we synthesized a pair of positional isomers by attaching a small electron-donating pyrrolidinyl group at ortho- and para-positions of a conjugated core. These isomers exhibited totally different fluorescent properties. PDB2 exhibited obvious aggregation-induced emission properties. In contrast, PDB4 showed the traditional aggregation-caused quenching effect. Their different fluorescent properties were investigated by absorption spectroscopy, fluorescence spectroscopy, density functional theory calculations and single-crystal structural analysis. These results indicated that the substituent position of the pyrrolidinyl groups affects the twisted degree of the isomers, which further induces different molecular packing modes, thus resulting in different fluorescent properties of these two isomers. This molecular design concept provided a new accurate strategy for designing new aggregation-induced emission luminogens.

Highlights

Fujian Provincial Key Laboratory of Screening for Novel Microbial Products, Fujian Institute of Microbiology, CAS Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Key Laboratory of Nanomaterials, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Department of Medicinal Chemistry, School of Pharmaceutical Engineering, Shenyang Pharmaceutical
The UV/vis absorption and emission properties of PDB2 and PDB4 were measured in the dimethyl sulfoxide (DMSO) solution
The strong absorption band of PDB2 was attributed to spin-allowed π–π* transitions of the compound, and the relatively weak absorption peaks could be assigned to an intramolecular charge transfer (ICT), which was induced by the D-A units, pyrrolidinyl as the electron donor group and cyano as the electron acceptor group

Summary

Photophysical Properties

The UV/vis absorption and emission properties of PDB2 and PDB4 were measured in the dimethyl sulfoxide (DMSO) solution. When the pyrrolidinyl group was changed from a para-position to ortho-position, the corresponding compound PDB2 exhibited a red-shift and peaked at 676 nm in the emission spectrum (Figure 1b). These results demonstrated that the ICT emission could be controlled well by changing the position of D-A units. Upon enhancing f w from 0 to 90%, a significant increase in the PDB2 fluorescence intensity was observed and the maximum emission wavelength of PDB2 changed from 600 nm to 650 nm due to the ICT effect resulting from an increased solvent polarity. Intensity (f) Emission intensity changes of PDB4 in different of to other of fraction points). The AIE properties of PDB2 and PDB4 were further investigated by dissolving them

Intramolecular

Crystal Structure

Mechanofluorochromic Properties

Synthesis

Synthetic routes condition:

Conclusions