Impacts of Fluorination at the Ortho ‐Position of Carboxy Groups on Tetrakis(biphenyl)ethene‐Based Hydrogen‐Bonded Framework

Fluorination of building block molecules is one of the effective engineering approaches to modulate molecular assembly in crystalline organic materials. Herein, we constructed a hydrogen-bonded organic framework (HOF) from a tetraphenylethene derivative, F-CBPE, possessing 3,5-difluoro-4-carboxyphenyl groups. The introduction of fluorine atoms in ortho-positions of the carboxy group makes the conformation of the arms more twisted, resulting in a framework structure different from that formed with the pristine molecule. The resulting HOF, F-CBPE-1(MeBz), is composed of sql-topological hydrogen-bonded network sheets accumulating in a staggered manner without interpenetration; while, the HOF of the pristine compound (CBPE) is composed of three-directionally interpenetrated sql-network sheets. Fluorescence spectroscopy and single-crystal microscopy revealed key features of the photophysical behavior of these HOFs. The solvated F-CBPE HOF exhibits blue emission due to an intramolecular charge transfer (ICT) event occurring in <15 ps, whereas desolvation induces a red shift, which is attributed to excimer-like species formed in 120 ps and arising from changes in the stacking arrangement of the layers. These findings show the effect of fluorination on the structures and fluorescence behavior of tetraphenylethene-based HOFs, which were thoroughly compared to the pristine CBPE molecule and related derivatives.