Heptamethine cyanine dyes, typified by indocyanine green, have been extensively employed as bioimaging indicators and theranostic agents. Significant efforts have been made to develop functional heptamethine cyanine dyes with outstanding bioimaging and theranostic utilities. In this work, we rationally designed and successfully developed a novel indolium-like heptamethine cyanine dye by installing indolium-derived polycyclic aromatic hydrocarbons on the terminal ends of a conjugated polyene backbone. This dye showed excellent photostability and showed bright fluorescent emission in the second near-infrared (NIR-II) window with a peak at approximately 1120 nm. Such long wavelength emission prompted a superior bioimaging resolution in vivo. In particular, this NIR-II dye had the remarkable capability of marking the blood vessels of the hindlimbs, abdomens, and brains of mice. More significantly, this dye involved a typical indolium-like heptamethine skeleton and exhibited two strong absorption bands in the 700–1300 nm NIR range, which endowed it with an intrinsic tumor-targeting capability and a high photothermal conversion efficiency (up to 68.2%), serving for the photothermal therapy of tumors under the guidance of NIR-II fluorescence imaging. This work provides an efficient design strategy for achieving indolium-like heptamethine cyanine dyes with further NIR-II emission.
Bibliographical noteFunding Information:
This work was supported by the National Basic Research Foundation of China (no. 2017YFA0505202). J.Y. acknowledges financial support from the National Natural Science Foundation of China (nos. 21676113 and 21772054); the Distinguished Young Scholar of Hubei Province (no. 2018CFA079); and the 111 Project B17019; the Scholar Support Program of CCNU (no. 0900-31101090002). X.L. gratefully acknowledges financial support from A*STAR under its Advanced Manufacturing and Engineering Program (no. A2083c0051) and the Ministry of Education, Singapore (no. MOE-MOET2EP10120-0007). J.Y. is supported by grants from the 619 National Creative Research Initiative programs of the 620 National Research Foundation of Korea, funded by 621 the Korean government (no. 2021R1A6A1A10039823). The authors are grateful for the supercomputing resources of SUTD-MIT IDC and the National Supercomputing Centre (Singapore).
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- biological application
- fluorescent probe
- heptamethine cyanine
- molecular design
- second near-infrared emission