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Suppressing Nonradiative Decay in BF2 Formazanates via Donor Bromination for Cancer Phototheranostics
Hanming Dai1, Jinjun Shao1, Dan Lei1
1State Key Laboratory of Flexible Electronics (LoFE) & Institute of Advanced Materials (IAM), School of Flexible Electronics (Future Technologies), Nanjing Tech University, Nanjing 211816, China.
Abstract:
Dominant nonradiative decay pathways in second-near-infrared (NIR-II) small-molecule fluorescent dyes critically impair both radiative emission and intersystem crossing (ISC) efficiencies, limiting their utility in fluorescence imaging (FLI) and phototherapy. Herein, we report a donor bromination strategy to suppress nonradiative decay in a boron difluoride (BF2) formazanate dye BDFTBr for NIR-II FLI-guided tumor photothermal and photodynamic therapy. Compared with the unbrominated analogue BDFTH, BDFTBr with donor bromination maintains a stereoscopic conformation and suppresses intramolecular vibrations, reducing vibrationally induced nonradiative heat dissipation and enhancing the fluorescence quantum yield by ∼3.75-fold. Additionally, donor bromination narrows the singlet-triplet energy gap (ΔES-T) and facilitates ISC, leading to the improved generation of multiple reactive oxygen species, even under the hypoxic tumor microenvironment. In vitro and in vivo studies confirm that BDFTBr nanoparticles enable efficient NIR-II FLI-guided tumor ablation with minimal systemic toxicity. This work provides a generalizable strategy for suppressing nonradiative decay in NIR-II small-molecule fluorescent dyes, advancing their potential in multimodal cancer phototheranostics.
Insights
A new bromination strategy enhances near-infrared fluorescent dyes for cancer therapy. This method improves fluorescence imaging and phototherapy by reducing energy loss and boosting therapeutic effects, leading to effective tumor ablation with low toxicity.
Area of Science:
- Materials Science
- Biomedical Engineering
- Organic Chemistry
Background:
- Nonradiative decay pathways significantly limit the performance of second-near-infrared (NIR-II) small-molecule fluorescent dyes in fluorescence imaging (FLI) and phototherapy.
- Efficient radiative emission and intersystem crossing (ISC) are crucial for effective FLI and phototherapy applications.
Purpose of the Study:
- To develop a donor bromination strategy to suppress nonradiative decay in NIR-II fluorescent dyes.
- To enhance the utility of boron difluoride (BF2) formazanate dyes for NIR-II FLI-guided tumor photothermal and photodynamic therapy.
Main Methods:
- Synthesized a brominated boron difluoride (BF2) formazanate dye (BDFTBr) and compared it with its unbrominated analogue (BDFTH).
- Investigated the effects of donor bromination on dye conformation, intramolecular vibrations, fluorescence quantum yield, and singlet-triplet energy gap (ΔEs-T).
- Evaluated the dye's performance in vitro and in vivo for NIR-II FLI-guided tumor ablation, including reactive oxygen species generation and systemic toxicity.
Main Results:
- Donor bromination in BDFTBr suppressed intramolecular vibrations and reduced nonradiative heat dissipation, enhancing the fluorescence quantum yield by approximately 3.75-fold compared to BDFTH.
- Bromination narrowed the singlet-triplet energy gap (ΔEs-T), facilitating intersystem crossing (ISC) and improving reactive oxygen species generation, even in hypoxic tumor environments.
- BDFTBr nanoparticles demonstrated efficient NIR-II FLI-guided tumor ablation with minimal systemic toxicity in in vitro and in vivo studies.
Conclusions:
- The donor bromination strategy is effective in suppressing nonradiative decay in NIR-II small-molecule fluorescent dyes.
- BDFTBr shows significant potential as a theranostic agent for multimodal cancer treatment, combining NIR-II FLI with photothermal and photodynamic therapy.
- This approach offers a generalizable method for advancing the development of NIR-II fluorescent dyes for cancer phototheranostics.
