Skeletal Distortion Manipulation in 2D–3D-Fused Boron Clusters Enables Solid-State Luminescence and Photothermal Conversion

Abstract Luminescent π-conjugated materials are central to modern optoelectronics, yet they are typically constructed from planar, rigid molecular frameworks. Herein, we introduce a conceptually distinct luminescent molecular platform based on three-dimensional (3D) boron cluster-fused conjugated heterocycles. Specifically, a phosphorus-containing heterocycle and a nitrogen-containing heterocycle were designed and synthesized. Both compounds exhibit typical aggregation-induced emission behavior through an skeletal distortion mechanism, which differs from the conventional restriction of intramolecular rotation. Comprehensive photophysical studies and theoretical calculations reveal that their weak emission in solution arises from efficient nonradiative decay driven by excited-state skeletal distortion, whereas this distortion is effectively suppressed in the aggregated state, resulting in bright luminescence. Exploiting this mechanism, we further developed an NIR-II luminogen incorporating a 2D–3D boron cluster-fused conjugated moiety that shows efficient photothermal conversion and enables multimodal imaging-guided photothermal therapy of tumors. Moreover, the boron-rich framework provides high boron content and favorable cellular boron uptake, highlighting its potential as a boron delivery agent for boron neutron capture therapy (BNCT). Overall, this work establishes 3D boron-cluster-fused conjugation as a versatile molecular strategy for regulating excited-state processes and constructing multifunctional phototheranostic materials.