Flexible Designing Strategy to Construct Activatable NIR-II Fluorescent Probes with Emission Maxima beyond 1200 nm

Activatable second near-infrared (NIR-II) fluorescent probes that can be lighted up by specific targets have attracted great attention because of their high specificity and resolution, which hold great promise in deep-tissue imaging. However, such probes were relatively rarely reported so far, and the emission maximum is still limited (mainly located at 900-1000 nm). To solve the problem, herein, we proposed a flexible strategy to modulate the emission wavelength of NIR-II fluorescent probes, and four proof-of-concept probes (WH-1, WH-2, WH-3, and WH-4) based on D-pi-A molecular skeleton were obtained. These probes can be activated by H2S and the emission maximum located from 925 to 1205 nm, which was attributed to the cooperation of elongating the pi-conjugated system and enhancing the electron-donating ability of the donor region. In these probes, WH-3 exhibited the combination of long excitation/emission (925/1140 nm) and moderate quantum yield as well as high sensitivity toward H2S, enabling us to track and image H2S in vivo with high contrast. We expected that such a molecular design strategy will become an important approach to developing activatable NIR-II fluorescent probes with long emission.

Automated summary

An approach to modulate the emission wavelength of NIR-II fluorescent probes by elongating the pi-conjugated system and enhancing the electron-donating ability of the donor region was proposed, resulting in the development of four proof-of-concept probes with emission maxima ranging from 925 to 1205 nm. Among these probes, WH-3 exhibited high sensitivity towards H2S and enabled in vivo tracking and imaging of H2S with high contrast. This molecular design strategy shows promise in developing activatable NIR-II fluorescent probes with long emission.