TPE-Containing Stimuli-Responsive Amino-Boranes: The Key Role of the Linker, Alkyl vs Aromatic

A series of tetraphenylethene (TPE)-functionalized, aldehyde-bearing amino-triarylboranes have been synthesized and comprehensively characterized. The AIE-active TPE unit was incorporated into the molecular backbone either via unconjugated alkyl linkers of varying lengths (BOTPE-C1, BOTPE-C3, and BOTPE-C6) or through a conjugated phenyl bridge (BOTPE-Ph). Owing to the switchable intramolecular B ← O bond, these compounds exhibit distinct luminescent responses to multiple external stimuli, including solvent polarity, temperature, and water content. The introduction of the TPE unit exerts differential impacts on the photophysical properties and stimuli-responsive properties of BOTPE derivatives, which are highly dependent on the type of linker used. With unconjugated linkers, the TPE unit does not significantly influence the emission intensity in a dilute solution. However, upon aggregation, the Förster resonance energy transfer (FRET) pathway is activated, thereby enhancing emission intensity. In the case of BOTPE-Ph, the conjugated phenyl linker imparts a typical aggregation-induced emission (AIE) behavior. This manifests as weak luminescence at low concentrations in polar solvents, with a significant enhancement in emission intensity upon aggregation.