Harnessing Host-Guest Conformational Matching for Efficient Near-Infrared Phosphorescence

Near-infrared room-temperature phosphorescence holds significant promise for applications in bioimaging, diagnosis, and treatment. However, their development is constrained by the energy gap law; especially, systems that combine structural simplicity with high efficiency remain extremely scarce. Herein, a "conformation matching" strategy based on aromatic thioketone units is proposed, enabling the rational construction of highly efficient host-guest near-infrared phosphorescent materials. This high efficiency is attributed to the conformation match between the guest and host, whereby the molecular stacking and conformation could be optimized to realize exciton localization. The longest emission peak of the obtained material is at 715 nm, and the maximum phosphorescence quantum yield is as high as 55.5%. Mechanistic studies further reveal that "conformation matching" can simultaneously regulate nonradiative decay, radiative transition rates, and triplet-triplet energy transfer processes, leading to a synergistic enhancement of performance. This work not only provides a new design strategy for highly efficient and compact near-infrared phosphorescent materials but also establishes conformation engineering as a crucial new dimension for tuning host-guest phosphorescence properties.