Solvent-Free Artificial Light-Harvesting System in a Fluid Donor with Highly Efficient Förster Resonance Energy Transfer

Multi-step Förster resonance energy transfer (FRET) plays a vital role in photosynthesis. While the energy transfer efficiency (ΦET) of a naturally occurring system can reach 95%, that of most artificial light-harvesting systems (ALHSs) is still limited. Herein, we propose a strategy to construct highly efficient ALHSs using a blue-emitting, supercooled ionic compound of naphthalimide (NPI) as the donor, a green-emitting BODIPY derivate as a relay acceptor, and a commercially available, red-emitting dye [rhodamine B (RhB)] as the final acceptor. The broad emission of the fluid donor can overlap simultaneously with the absorption of BODIPY and RhB, enabling the occurrence of a sequential FRET from NPI to BODIPY to RhB as well as a parallel FRET directly from NPI to RhB. These two complementary energy transfer routes lead to an overall ΦET up to 97.4%, which is the champion among all of the reported ALHSs and is also higher than that found in plants and photosynthetic bacteria. This strategy is universal, and ΦET of the system could be further improved by optimizing the structures of the fluid donor and relay acceptor.多步福斯特共振能量转移（Förster resonance energy transfer, FRET）在光合作用中发挥着不可或缺的核心作用。天然光合体系的能量转移效率（ΦET）可高达95%，但绝大多数人工光捕获体系（artificial light-harvesting systems, ALHSs）的能量转移效率仍存在显著局限。本文提出一种构建高效人工光捕获体系的策略：以蓝色发光的过冷萘酰亚胺（naphthalimide, NPI）离子化合物作为能量供体，以绿色发光的BODIPY衍生物作为中继受体，以市售红色发光染料罗丹明B（rhodamine B, RhB）作为最终受体。该流体供体的宽发射光谱可同时与BODIPY和RhB的吸收光谱形成重叠，从而同时实现两条互补的能量转移途径：一是从NPI到BODIPY再到RhB的级联FRET，二是从NPI直接到RhB的并行FRET。这两条途径协同作用使体系的总能量转移效率可达97.4%，为已报道的所有人工光捕获体系中的最优值，同时也高于植物与光合细菌中的能量转移效率。该策略具备普适性，通过优化流体供体与中继受体的分子结构，可进一步提升体系的能量转移效率。