One-Step Synthesis of Supramolecular Nanoparticles With Interlocking-Enhanced Two-Photon Fluorescence

Traditional organic two-photon excited fluorescence (TPEF) materials relying on extended π-conjugated backbones inherently suffer from complex synthesis, limited biocompatibility, and aggregation-caused quenching (ACQ). In this work, conceptually inspired by the interlocking design in engineering structures, we develop a facile one-step supramolecular assembly strategy to fabricate poly(2,5-diamino-1,4-benzenedithiol) (PMBT) supramolecular nanoparticles (SNPs). The SNPs are constructed through the synergistic interplay of disulfide polymerization, hydrogen bonding, and π-π stacking, resulting in an interlocking-enhanced, short-range locally ordered structure that lacks extended π-conjugated backbones. The interlocking architecture not only effectively suppresses nonradiative decay pathways by restricting molecular motion within the rigidified matrix, but also facilitates efficient exciton coupling and radiative recombination through enhanced interchain electronic communication. Consequently, PMBT SNPs exhibit favorable overall performance, including high aqueous stability, favorable fluorescence properties (quantum yield of 9% ± 1%, lifetime of 15.6 ns), exceptional two-photon absorption cross-section of up to 6.3 × 10⁵ GM at 800 nm excitation, favorable biocompatibility (>85% cell viability at 200 µg/mL for 48 h), and deep-tissue imaging capabilities. This work establishes a supramolecular engineering paradigm that harnesses intermolecular interactions, thereby enabling the development of high-performance two-photon clusterization-triggered emissive materials.