Bromine Substitution Improves the Photothermal Performance of -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 clinical requirements. In this work, we developed a bromine-substitution strategy to enhance the PTT of A-D-A'-D-A pi-conjugated molecules. The experimental results reveal that bromine substitution can notably enhance the absorptivity (epsilon) and photothermal conversion efficiency (PCE) of the pi-conjugated molecules, resulting in the brominated molecules generating two times more heat (epsilon 808 nmxPCE) than their unsubstituted counterpart. We disclose that the enhanced photothermal properties of bromine-substituted pi-conjugated molecules are a combined outcome of the heavy-atom effect, enhanced ICT effect, and more intense bromine-mediate intermolecular pi-pi stacking. Finally, the NIR-II tumor imaging capability and efficient PTT tumor ablation of the brominated pi-conjugated materials demonstrate that bromine substitution is a promising strategy for developing future high-performance NIR-II imaging-guided PTT agents. Bromine substitution enhances the photothermal properties of pi-conjugated phototheranostic molecules; this is the outcome of a combination of the heavy-atom effect, enhanced ICT effect, and more intense bromine-mediate intermolecular pi-pi stacking. The results demonstrate that bromine substitution is promising for developing high-performance NIR-II imaging-guided photothermal agents.image