Bright Near-Infrared Aggregation-Induced Emission Luminogens with Strong Two-Photon Absorption, Excellent Organelle Specificity, and Efficient Photodynamic Therapy Potential

Far-red
and near-infrared (NIR) fluorescent materials possessing
the characteristics of strong two-photon absorption and aggregation-induced
emission (AIE) as well as specific targeting capability are much-sought-after
for bioimaging and therapeutic applications due to their deep penetration
depth and high resolution. Herein, a series of dipolar far-red and
NIR AIE luminogens with a strong push–pull effect are designed
and synthesized. The obtained fluorophores display bright far-red
and NIR solid-state fluorescence with a high quantum yield of up to
30%, large Stokes shifts of up to 244 nm, and large two-photon absorption
cross-sections of up to 887 GM. A total of three neutral AIEgens show
specific lipid droplet (LD)-targeting capability, while the one with
cationic and lipophilic characteristics tends to target the mitochondria
specifically. All of the molecules demonstrate good biocompatibility,
high brightness, and superior photostability. They also serve as efficient
two-photon fluorescence-imaging agents for the clear visualization
of LDs or mitochondria in living cells and tissues with deep tissue
penetration (up to 150 μm) and high contrast. These AIEgens
can efficiently generate singlet oxygen upon light irradiation for
the photodynamic ablation of cancer cells. All of these intriguing
results prove that these far-red and NIR AIEgens are excellent candidates
for the two-photon fluorescence imaging of LDs or mitochondria and
organelle-targeting photodynamic cancer therapy.