Journal
SMALL
Volume 16, Issue 19, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/smll.202000680
Keywords
carbon dots; D-pi-A; in vivo imaging; multiphoton absorptions; near-infrared
Categories
Funding
- National Natural Science Foundations of China [51772001]
- Key Laboratory of Structure and Functional Regulation of Hybrid Materials (Anhui University), Ministry of Education, Hefei, P. R. China
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Carbon dots (CDs), with excellent optical property and cytocompatibility, are an ideal class of nanomaterials applied in the field of biomedicine. However, the weak response of CDs in the near-infrared (NIR) region impedes their practical applications. Here, UV-vis-NIR full-range responsive fluorine and nitrogen doped CDs (N-CDs-F) are designed and synthesized that own a favorable donor-pi-acceptor (D-pi-A) configuration and exhibit excellent two-photon (lambda(ex) = 1060 nm), three-photon (lambda(ex) = 1600 nm), and four-photon (lambda(ex) = 2000 nm) excitation upconversion fluorescence. D-pi-A-conjugated CDs prepared by solvothermal synthesis under the assistance of ammonia fluoride are reported and are endowed with larger multiphoton absorption (MPA) cross sections (3PA: 9.55 x 10(-80) cm(6) s(2) photon(-2), 4PA: 6.32 x 10(-80) cm(8) s(3) photon(-3)) than conventional organic compounds. Furthermore, the N-CDs-F show bright deep-red to NIR fluorescence both in vitro and in vivo, and can even stain the nucleoli of tumor cells. A plausible mechanism is proposed on the basis of the strong inter-dot and intra-dot hydrogen bonds through N-H center dot center dot center dot F that can facilitate the expanding of conjugated sp(2) domains, and thus not only result in lower highest occupied molecular orbital-lowest unoccupied molecular orbital energy level but also larger MPA cross sections than those of undoped CDs.
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