Activatable Heavy-Atom-Free Photosensitizer with Large Stokes Shift and a NIR-II Emission Harnessing Rhodamine Ring-Opening Strategy
Chuangjun Liu, Qihang Ding, Yinling Xu, Qian Bai, Yingchun Jiang, Yihang Shi, Mengru Ma, Yuanyuan Sun, Qiang Lü, Xinyu Chen, Junhang Liu, Gaoyu Yi, Yang Yang, Tiezhen Wang, Shuai Zhang, Pengfei Wang, Jong Seung Kim
Abstract
Activatable photosensitizers (PSs) generating 1 O 2 only under specific conditions can minimize concomitant injury to normal tissues. Heavy-atom-free PSs hold the merits of low dark toxicity, long triplet-state lifetimes, good photostability, and relatively low cost. PSs with emission in the second near-infrared (NIR-II) window are highly valuable for deep-tissue, high-contrast imaging. Herein, we have designed and synthesized a series of heavy-atom-free PSs by a one-step reaction between an easily accessible rhodamine derivative and commercially available thiophene aldehydes. One of the as-prepared PSs, 2b-3T, exhibits emission maxima at 810 nm and tails to the NIR-II region at 1140 nm, together with large Stokes shift (178 nm). Importantly, the newly developed PSs, featuring functional carboxylic acid groups, present promising opportunities as versatile platforms for creating activatable PSs. To validate our concept, we developed Cu 2+ /pH-activatable PSs using the spirocyclization mechanism of rhodamine. Ultimately, we showcased the effectiveness of these innovative PSs in photodynamic therapy through in vitro experiments.