Engineering Tetraphenylethene-Based Z and E Stereoisomers: Structural Analysis and Sensing Application

Abstract

The exploration of Z/E stereoisomers represents an interesting and significant endeavor in molecular engineering. We developed three pairs of tetraphenylethylene (TPE) derivatives modified by heteroatom-containing trivalent arylboron and/or tris(2-methylpyridyl)amine (TPA) to explore the differences in the optical properties, morphologies, and sensing applications in the Z and E stereoisomers. They exhibit similar photophysical properties in the solution state, and obvious difference in the amorphous aggregate and crystal states. All E-isomers exhibit tighter molecular packing and spatial interactions compared with the Z-isomers, resulting in longer-wave fluorescence emission. The single-crystal X-ray structures reveal the molecular configurations and luminescence mechanisms, allowing for a discussion on the pattern of the through-space charge transfer. The ultramarine fluorescent emission of Z-isomer cis-BB should originate from staggerarranged molecular pair, and the green fluorescence of E-isomer trans-BB should originate from the molecular J-type aggregation. In addition, the E isomer trans-BN shows a highly selective and sensitive response to HPO4 2-based on the restriction of intramolecular rotation-induced fluorescence enhancement of TPE and the synergistic coordination effect of triarylboron and metal ion chelated by TPA. This work extends the family of stereoisomers available in molecular engineering with new structures and correlated morphologies and functionalities, and demonstrates the design, separation, and evaluation of the Z and E stereoisomers of TPE and their derivatives.