Asymmetric π-Extension Design of Long Wavelength Rhodamine Derivatives for Imaging and Phototherapy

Abstract

Rhodamine dyes have been extensively explored for bioimaging and therapeutic applications over the past few decades. However, it remains a challenge to design long-wavelength and large Stokes shift rhodamine derivatives to meet the requirements of fluorescence imaging and phototherapy in deep living tissues. In this work, a pyridine aromatic unit was inserted into the rhodamine derivatives (AC-Fluor: ACF) skeleton to prepare a series of stable rhodamine derivatives, named ACFPs, to achieve long emission wavelength (>650 nm) and large Stokes shift (~60 nm) by tuning the conjugated systems and electronic symmetry. Moreover, ACFPs are capable of continuously producing superoxide radical (O₂⁻⋅) under long wavelength irradiation. This study presents a novel paradigm for improving the optical properties of rhodamine, which has led to the development of a novel tool for image-guided phototherapy for cancer treatment.