Diagnostic Absolute Configuration Determination of Tetraphenylethene Core-Based Chiral Aggregation-Induced Emission Compounds: Particular Fingerprint Bands in Comprehensive Chiroptical Spectroscopy

Tetraphenylethylene
(TPE) and its derivatives are the typical aggregation-induced
emission (AIE) compounds with helical chirality, and they have enormous
applications potential in chiral sensor, asymmetric catalyst, optoelectronic
materials, and so on. The aggregation-induced helical chirality of
TPE and its derivatives can only be observed in condensed phase such
as crystalline or film state. The accurate determination of absolute
configuration (AC) of TPE core compounds is complicated and difficult,
especially when there is no heavy atoms exist in their structures.
Herein, we demonstrate a powerful and convenient method to quickly
determine the helical chirality of these stereochemically labile TPE
core compounds through the combination of comprehensive solid-state
chiroptical spectroscopy and theoretical calculation. Our study reveals
that from lower to higher energy of the fingerprint region, the first
electronic circular dichroism (ECD) band in the 300–450 nm
or the first most intensive vibrational circular dichroism (VCD) peak
in the 875–730 cm–1 can be used as the diagnostic
bands for the AC determination of the TPE core with the fixed chirality.
If these diagnostic bands cannot be observed in ECD or VCD spectra,
the helical chirality of the atropisomers of TPE derivatives is not
fixed. The explicit AC determination of TPE core contributes to the
study of the helical chirality of supramolecular TPE core derivatives
and allows for the further fabrication of novel chiral AIE functional
materials.