Templated freezing assembly precisely regulates molecular assembly for free-standing centimeter-scale microtextured nanofilms

Ultrasmall Organic Nanocrystal Photocatalyst Realizing Highly Efficient Symmetry Breaking Charge Separation and Transport

The high exciton binding energy and short exciton diffusion length (typical 5-10 nm) of organic photocatalysts (OPCs) hinder efficient charge separation and subsequent charge transfer, limiting their potential for solar energy conversion. Inspired by the symmetry breaking charge separation (SBCS) in natural photosystem II, we employed a freeze assembly (FA) strategy to assemble symmetric perylene diimide (PDI) dimers into ultrasmall (sub-5 nm) nanocrystals (NCs) with ordered molecular stacking, exhibiting SBCS characteristics. The SBCS NCs (p-5 nm) showed 12.3-fold enhancement in charge separation efficiency compared to non-SBCS NCs (PDI-5 nm). Furthermore, the charge transfer efficiency in p-5 nm (94.7%) was 1.6 times greater than that of weak SBCS NCs (m-5 nm, 60.4%). Consequently, we achieved a comparable photocatalytic hydrogen evolution rate (1824 μmol h-1 g-1) among the PDI-based photocatalysts in p-5 nm. This study highlights the importance of ultrasmall NCs in fulfilling bioinspired SBCS and the potential of the FA strategy for developing high-performance OPCs.

Preparation of Ultrasmall AIE Nanoparticles with Tunable Molecular Packing via Freeze Assembly

Advances in the development of aggregation-induced emission luminogens (AIEgens) depend on understanding how the molecular packing affects their luminescent properties and on making nanoparticles (NPs) with desired sizes. Although reported strategies have advanced the field, rational control of molecular packing and efficient fabrication of AIEgen NPs sub-5.5 nm in diameter remain pressing issues. Here we report a "freeze assembly" strategy, in which the diameter of AIEgen NPs can be precisely tuned from ∼3 nm to hundreds of nanometers, and a molecular packing in kinetically trapped states that are not easily captured by conventional assembly methods can be obtained, leading to tunable fluorescence emissions. Therefore, this study provides a significant tool to fabricate organic luminescent nanomaterials with diameters smaller than 5 nm, which is of critical importance for biomedical applications; meanwhile, tuning molecular packing in nanoparticles displaying different fluorescence may help to shed new light on the mechanism of AIEgens.