Substituent Group Variations Directing the Molecular Packing, Electronic Structure, and Aggregation-Induced Emission Property of Isophorone Derivatives

A series of new isophorone derivatives
(1–5), incorporating the heterocyclic
ring or aza-crown-ether
group, with large Stokes shifts (>140 nm), have been synthesized
and
characterized. 1–4 display aggregation-induced
emission behaviors, while dye 5 is highly emissive in
solution but quenched in the solid state. It was found that the tuning
of emission color of the isophorone-based compounds in the solid state
could be conveniently accomplished by changing the terminal substituent
group. The photophysical properties in solution, aqueous suspension,
and crystalline state, along with their relationships, are comparatively
investigated. Crystallographic data of 1–4 indicate that the existence of multiple intermolecular hydrogen
bonding interactions between the adjacent molecules restricts the
intramolecular vibration and rotation and enables compounds 1–4 to emit intensely in the solid state.
The size and growth processes of particles with different water fractions
were studied using a scanning electron microscope, indicating that
smaller globular nanoparticles in aqueous suspension are in favor
of fluorescence emissions. The above results suggest that substituent
groups have a great influence on their molecular packing, electronic
structure, and aggregation-induced emission properties. In addition,
fluorescence cell imaging experiment proved the potential application
of 5.