Octupolar AIEgens Photosensitizers With Enhanced Molar Absorptivity for Near-Infrared Phototheranostics

Abstract

High molar absorption coefficients (ε) in the near-infrared (NIR) region are critical for maximizing light-harvesting efficiency, enabling deep-tissue penetration, and enhancing reactive oxygen species (ROS) generation in phototheranostics. However, strong absorptivity at NIR wavelengths is challenging for organic luminogens due to intrinsically diminished oscillator strengths. We report a symmetry-guided molecular engineering approach to construct octupolar aggregation-induced emission luminogens (AIEgens) that overcome this limitation. Incorporating fused tetrahydroxanthylium (THX) acceptors into a D(A)₃ framework yields a four-fold enhancement in ε (5.47 × 10⁴ M⁻¹ cm⁻¹) at 670 nm compared to dipolar analogs (D-A), while achieving bright NIR-II emission at 963 nm. Femtosecond transient absorption spectroscopy reveals stronger ground-state bleaching and additional excited-state absorption in octupolar systems, correlating with enhanced light-harvesting. Density functional theory calculations demonstrate that symmetry-enabled dipole coupling activates additional S₀→S₂ transitions, explaining the high absorptivity. The octupolar architecture also reduces ΔE_ST and introduces low-lying excited states, promoting intersystem crossing and boosting ROS generation. This symmetry-driven design combines twisted conformations with AIE features to create a robust platform for bright NIR-II emission and advanced phototheranostic applications.

Keywords

aggregation-induced emission / molar absorptivity enhancement / NIR-II fluorescence imaging / octupolar molecular engineering / symmetry-breaking charge transfer

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2026 The Author(s). Aggregate published by SCUT, AIEI, and John Wiley & Sons Australia, Ltd.