posted on 2024-01-19, 17:37authored byTao Yuan, Qiming Xia, Zhiqiang Wang, Xinsheng Li, Hui Lin, Ju Mei, Jun Qian, Jianli Hua
Small-molecule dyes for fluorescence imaging in the second
near-infrared
region (NIR-II, 900–1880 nm) hold great promise in clinical
applications. Constructing donor–acceptor–donor (D–A–D)
architectures has been recognized to be a feasible strategy to achieve
NIR-II fluorescence. However, the development of NIR-II dyes via such
a scheme is hampered by the lack of high-performance electron acceptors
and donors. Diketopyrrolopyrrole (DPP), as a classic organic optoelectronic
material, enjoys strong light absorption, high fluorescence quantum
yield (QY), and facile derivatization. Nevertheless, its application
in the NIR-II imaging field has been hindered by its limited electron-withdrawing
ability and the aggregation-caused quenching (ACQ) effect resulting
from the planar structure of DPP. Herein, with DPP as an electron
acceptor and through donor engineering, we have successfully designed
and synthesized a DPP-based dye named T-27, in which the strong D–A
interaction confers excellent NIR absorption and high-brightness NIR-II
fluorescence tail emission. By strategically introducing long alkyl
chains on the donor unit to increase intermolecular spacing and reduce
the influence of solvent molecules, T-27 exhibits an improved anti-ACQ
effect in aqueous solutions. After being encapsulated into DSPE-PEG2000, T-27 nanoparticles (NPs) show a relative NIR-II fluorescence
QY of 3.4% in water, representing the highest value among the DPP-based
NIR-II dyes reported to date. The outstanding photophysical properties
of T-27 NPs enable multimode NIR-IIa bioimaging under 808 nm excitation.
As such, the T-27 NPs can distinguish mouse femoral vein and artery
and achieve cerebral vascular microscopic imaging with a penetrating
depth of 800 μm, demonstrating the capability for high-resolution
deep-tissue imaging. This work holds significant potential in the
field of bioimaging and provides a new strategy for developing bright
NIR-II dyes.