en.Wedoany.com Reported - A research team led by Dengxu Wang at Shandong University has discovered that siloxane can actively activate through-space conjugation (TSC) via a "dynamic encapsulation" mechanism, challenging the traditional view that it merely serves as an inert spacer in conjugated systems. With its flexible Si–O–Si backbone, siloxane has long been widely used in materials science and optoelectronics due to its good solubility and structural adaptability, but its intrinsic ability to regulate molecular aggregation and spatial arrangement has been overlooked. The team conducted photophysical characterization and theoretical calculations on siloxane-linked fluorescent polymers (SFPs), finding that these materials exhibit strong fluorescence in both solution and solid states, i.e., significant dual-state emission (DSE) properties. This indicates that siloxane can actively activate through-space conjugation, spatially coordinating chromophore interactions and promoting electronic communication in non-covalent assemblies.
To elucidate this mechanism, the team synthesized a series of polymers, SFP-1 to SFP-7, by linking various aromatic chromophores (spirobifluorene, biphenyl, triphenylamine, etc.) to flexible siloxane bridges via Heck coupling reactions. By comparing the optical properties, molecular conformations, frontier molecular orbital distributions, and aggregation morphologies of SFPs with their corresponding monomer chromophores, the study revealed that the siloxane bridge is not merely a simple linking unit but, through a "dynamic encapsulation" mechanism, wraps and assembles two adjacent aromatic chromophores into spatially proximate non-covalently coupled assemblies. This spatial arrangement enables effective orbital overlap between chromophores, activating through-space conjugation and enhancing electron delocalization. Consequently, SFPs achieve a photoluminescence quantum yield of up to 92.7% in solution. Additionally, the flexibility of the siloxane chain suppresses intramolecular vibrational relaxation, reducing non-radiative decay. In contrast, aromatic monomers without siloxane bridges tend to undergo tight π–π stacking, leading to aggregation-caused quenching (ACQ) and diminished luminescence.
The researchers further applied SFPs to practical sensing, demonstrating high-performance detection of the herbicide Trifluralin. The SFP-based probe achieved a detection limit as low as 0.313 μM, exhibited excellent selectivity against interferents, and enabled visual detection under ambient daylight without external instruments, offering practical advantages over traditional fluorescent probes. In the field of UV shielding, SFPs also show promise as stable, flexible components. Their inherent stability, combined with strong UV absorption and fluorescence conversion capabilities, makes them ideal candidates for UV-protective windows, goggles, and materials designed to filter high-energy blue light. This study systematically establishes, for the first time, the core mechanism of siloxane-activated through-space conjugation, opening new avenues for the design of siloxane-containing functional luminescent materials and providing a mechanistic foundation for applications in sensing, optoelectronics, UV shielding, and beyond.
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