Three Isomeric Tetraphenylethylene-pyridine Compounds: Synthesis, Crystal Structures, and Photophysical Properties

Many aggregation-induced emission (AIE) molecules based on tetraphenylethylene (TPE) structure have been synthesized, but a clear understanding of the photophysical difference between different isomeric pyridyl-based tetraphenylethylene molecules remains elusive. Herein, we designed a series of isomeric tetraphenylethylene-pyridines (o-Py-TPE, m-Py-TPE, p-Py-TPE) to investigate the influence of the position of N atoms in the pyridine subunit on the photophysical property of the whole molecule by detailed DFT calculations and single-crystal structures analysis. All compounds show typical AIE properties, and notably, the meta pyridyl isomer (m-Py-TPE) shows the highest solid photoluminescence quantum yield (PLQY) up to 64.56%. Further investigation and DFT calculations indicate that the center C=C bond dihedral angles of the TPE subunit in the solid state of these compounds, which are affected by C=H center dot center dot center dot pi interaction, play a vital role in their emission and PLQY properties. This work provides underlying principles for the design of pyridyl-based TPE molecules with high photoluminescent performance in the future.

Automated summary

We designed a series of isomeric tetraphenylethylene-pyridines and investigated the influence of the position of N atoms in the pyridine subunit on the photophysical property of the whole molecule. All compounds exhibited typical aggregation-induced emission properties, and the meta pyridyl isomer showed the highest solid photoluminescence quantum yield. Further analysis suggested that the dihedral angles of the TPE subunit's C=C bond played a vital role in their emission and quantum yield properties. This work provides underlying principles for the design of pyridyl-based tetraphenylethylene molecules with high photoluminescent performance in the future.