Hypsochromic Shift Donor-Acceptor NIR-II Dye for High-Efficiency Tumor Imaging

Nowadays, second near-infrared window (NIR-II) dyes'developmentfocuses on pursuing a longer absorption/emission wavelength and higherquantum yield, which usually means an extended pi conjugationsystem, resulting in an enormous molecular weight and poor druggability.Most researchers thought that the reduced pi conjugation systemwould bring on a blueshift spectrum that causes dim imaging qualities.Little efforts have been made to study smaller NIR-II dyes with areduced pi conjugation system. Herein, we synthesized a reduced pi conjugation system donor-acceptor (D-A) probe TQ-1006(Em = 1006 nm). Compared with its counterpart donor-acceptor-donor(D-A-D) structure TQT-1048 (Em = 1048 nm), TQ-1006 exhibited comparableexcellent blood vessels, lymphatic drainage imaging performance, anda higher tumor-to-normal tissue (T/N) ratio. An RGD conjugated probeTQ-RGD showed an extra high contrast tumor imaging (T/N >= 10),further proving D-A dyes' excellent NIR-II biomedical imagingapplications. Overall, the D-A framework provides a promising approachto designing next-generation NIR-II fluorophores.

Automated summary

Nowadays, the development focus of NIR-II dyes is on achieving longer absorption/emission wavelength and higher quantum yield. However, this often leads to larger molecular weight and poor druggability due to the extended pi conjugation system. In this study, a reduced pi conjugation system D-A probe (TQ-1006) was synthesized, showing comparable excellent imaging performance and a higher T/N ratio compared to its D-A-D counterpart (TQT-1048). A conjugated probe (TQ-RGD) demonstrated extra high contrast tumor imaging, further proving the excellent NIR-II biomedical imaging applications of D-A dyes. Overall, the D-A framework offers a promising approach for designing next-generation NIR-II fluorophores.