The Improving Effect of Bromine‐Substitution on Photothermal Performance of π‐Conjugated Phototheranostic Molecules

NIR‐II fluorescence imaging‐guided photothermal therapy (PTT) has been widely investigated due to its great application potential in tumor theranostics. PTT is an effective and non‐invasive tumor treatment method that can adapt to tumor hypoxia; nevertheless, simple and effective strategies are still desired to develop new materials with excellent PTT properties to meet the clinical requirements. In this work, we arise a bromine‐substitution strategy to enhance the PTT of A‐D‐A’‐D‐A π‐conjugated molecules. The experimental results reveal that bromine‐substitution can notably enhance the absorptivity (ε) and photothermal conversion efficiency (PCE) of the π‐conjugated molecules, resulting in the brominated molecules generating two‐fold more heat (ε808 nm × PCE) compared with the non‐substituted counterpart. We declare that the enhanced photothermal properties of bromine‐substituted π‐conjugated molecules are a combined outcome of the heavy‐atom effect, enhanced ICT effect, and bromine‐mediate more intense intermolecular π‐π stacking. Finally, the NIR‐II tumor imaging capability and efficient PTT tumor ablation of the brominated π‐conjugated materials demonstrate that bromine‐substitution will become a promising strategy for developing high‐performance NIR‐II imaging‐guided PTT agents in the future.