Key Takeaways & Executive Findings
- •• • TPACN exhibits a fluorescence peak at 1086 nm with a fluorescence quantum yield of 1.55% in DCM, representing a marked red-shift and enhanced emission for aza-BODIPY dyes, which is critical for deep-tissue imaging. • • TPACN NPs in aqueous solution maintain a FLQY of 0.20% and achieve a photothermal conversion efficiency (PCE) of 39% under 808 nm irradiation, demonstrating a synergistic balance between radiative and non-radiative decay for dual-modal imaging and photothermal therapy. • • The introduction of triphenylamine (TPA) donors and cyano (–CN) acceptors strengthens intramolecular charge transfer (ICT), broadening NIR absorption and enabling excitation at 808 nm, a wavelength with deeper tissue penetration. • • The sterically twisted TPA units effectively alleviate aggregation-caused quenching (ACQ), preserving fluorescence in the nanoparticle formulation, which is essential for in vivo imaging and therapeutic efficacy.
Abstract
Organic fluorophores operating in the second near-infrared (NIR-II, 1000–1700 nm) window are highly attractive for cancer phototheranostics. Yet, the advancement of aza-BODIPY-based NIR-II dyes remains challenging due to their limited spectral tunability and diminished fluorescence quantum yields (FLQY) under physiological conditions. Herein, we propose a rational donor-acceptor (D-A) molecular engineering strategy to construct an aza-BODIPY fluorophore, TPACN, featuring intramolecular charge transfer (ICT)-enhanced NIR-II emission and balanced photothermal performance. By introducing electron-rich triphenylamine (TPA) donors and peripheral cyano (–CN) acceptors, the optimized D-A coupling significantly strengthened the ICT effect, leading to broadened NIR absorption, a markedly red-shifted fluorescence peak at 1086 nm, and an exceptional fluorescence quantum yield of 1.55% in dichloromethane (DCM). When encapsulated in F127, TPACN nanoparticles (TPACN NPs) maintained a high aqueous FLQY of 0.20%, accompanied by a notable photothermal conversion efficiency (PCE) of 39% under 808 nm irradiation. The sterically twisted TPA units effectively alleviated aggregation-caused quenching (ACQ) and fine-tuned the excited-state energy dissipation pathways, realizing a synergistic balance between radiative (fluorescence) and non-radiative (heat) relaxation. Benefiting from these optimized photophysical properties, TPACN NPs achieved high-resolution NIR-I photoacoustic and NIR-II fluorescence dual-modal imaging, enabling accurate tumor visualization and efficient photothermal ablation in vivo. This work introduces a general design paradigm that exploits ICT modulation and steric engineering to overcome the intrinsic fluorescence bottleneck of aza-BODIPY systems, offering new molecular insights for the advancement of high-performance NIR-II dyes for precision phototheranostics.
1. Introduction
Conventional cancer theranostics rely on imaging modalities such as CT, PET, SPECT, and MRI, which suffer from limited sensitivity, low spatial resolution, and lack of real-time feedback. Fluorescence imaging in the NIR-II window (1000–1700 nm) offers reduced tissue scattering and autofluorescence, enabling high-resolution tumor visualization. However, existing NIR-II fluorophores often exhibit poor fluorescence quantum yields and limited spectral tunability, particularly for aza-BODIPY derivatives, hindering their clinical translation.
This work addresses the bottleneck by employing a donor-acceptor engineering strategy to construct TPACN, an aza-BODIPY fluorophore with ICT-enhanced NIR-II emission. By incorporating electron-rich TPA donors and cyano acceptors, the dye achieves a fluorescence peak at 1086 nm and a quantum yield of 1.55% in DCM, with a balanced photothermal conversion efficiency of 39% in aqueous nanoparticles. This design not only overcomes the ACQ effect but also optimizes the excited-state energy dissipation, enabling dual-modal NIR-I photoacoustic and NIR-II fluorescence imaging for precise tumor phototheranostics.
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Leichen Wang, Qing Shen, Weili Wang, Xu Sun, Jinjun Shao, Su Jing, Xiaochen Dong (2026). Donor-acceptor engineered aza-BODIPY fluorophore with intramolecular charge transfer-enhanced NIR-II emission for tumor phototheranostics. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4031-6
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Frequently Asked Questions
What is the mechanism behind the enhanced NIR-II emission and photothermal performance of TPACN?
The enhanced NIR-II emission and photothermal performance arise from the donor-acceptor (D-A) molecular engineering, which strengthens intramolecular charge transfer (ICT). The electron-rich triphenylamine (TPA) donors and cyano (–CN) acceptors create a strong push-pull effect, leading to a red-shifted fluorescence peak at 1086 nm and a high fluorescence quantum yield of 1.55% in DCM. The sterically twisted TPA units also suppress aggregation-caused quenching (ACQ), maintaining a quantum yield of 0.20% in aqueous nanoparticles. The balance between radiative and non-radiative decay is tuned to achieve a photothermal conversion efficiency of 39% under 808 nm irradiation.
How does TPACN NPs achieve dual-modal imaging and photothermal therapy?
TPACN NPs exhibit strong NIR-II fluorescence and photoacoustic signals, enabling dual-modal imaging. The fluorescence quantum yield of 0.20% in aqueous solution allows for high-resolution NIR-II fluorescence imaging, while the efficient non-radiative decay contributes to photoacoustic signal generation. Under 808 nm laser irradiation, the NPs achieve a photothermal conversion efficiency of 39%, enabling effective photothermal ablation of tumors. This synergistic combination allows for accurate tumor visualization and therapy.
What are the advantages of using aza-BODIPY-based dyes for NIR-II imaging compared to other fluorophores?
Aza-BODIPY dyes offer several advantages, including good photostability, tunable absorption and emission in the NIR region, and the ability to incorporate various functional groups. However, they often suffer from low fluorescence quantum yields and limited spectral tunability. This work demonstrates that donor-acceptor engineering can overcome these limitations, achieving a fluorescence peak at 1086 nm and a quantum yield of 1.55% in DCM, which is competitive with other NIR-II fluorophores. Additionally, the twisted structure of TPA units helps mitigate ACQ, making them suitable for biological applications.
What is the significance of the photothermal conversion efficiency (PCE) of 39% for TPACN NPs?
A PCE of 39% under 808 nm irradiation is notably high for organic photothermal agents. This efficiency ensures that sufficient heat is generated to induce tumor cell death while minimizing the required laser power, thereby reducing potential damage to surrounding healthy tissues. The high PCE, combined with the NIR-II fluorescence imaging capability, positions TPACN NPs as a promising theranostic agent for precise cancer treatment.
How does the encapsulation in F127 affect the photophysical properties of TPACN?
Encapsulation in F127 forms nanoparticles (TPACN NPs) that maintain the fluorescence quantum yield at 0.20% in aqueous solution, which is lower than in DCM (1.55%) but still sufficient for imaging. The encapsulation also preserves the photothermal conversion efficiency at 39%, indicating that the non-radiative decay pathways are retained. The F127 matrix provides biocompatibility and colloidal stability, essential for in vivo applications.
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