Asymmetric Boron-Cored Aggregation-Induced Emission Luminogen with Multiple Functions Synthesized through Stepwise Conversion from a Symmetric Ligand

Multifunction
luminogens have emerged as promising candidates in
high-performance sensor and imaging systems. Concise approaches to
the synthesis of such molecules are urgently required both for fundamental
research and technological applications. In this study, a new symmetric
ligand of di­(2-hydroxyphenyl)­phthalazine with multiple binding sites
around a phthalazine unit was readily synthesized, which could be
converted efficiently into an asymmetric luminogen (OBN-DHPP) through the formation of oxygen–boron–nitrogen bonding.
This molecule has a twistable π-extended backbone with a tetracoordinated
boron core bearing two bulky phenyl groups, giving it abundant optical
properties including a large Stokes shift piezochromism and aggregation-induced
emission enhancement. Importantly, the presence of a free phenolic
hydroxyl group in the backbone of OBN-DHPP enables the
incorporation of various functional moieties into the asymmetric luminogen.
As an example, polyethylene glycol (PEG)-modified luminogen (OBN-DHPP-PEG45) was synthesized. In
the aqueous medium, OBN-DHPP-PEG45 could self-assemble into spherical nanoparticles with low cytotoxicity
and excellent emission performance as well as high solubility. The
results of flow cytometry and fluorescence microscopy reveal that
these nanoparticles could be internalized successfully by HeLa cells,
demonstrating their potential application in bioimaging.