Ultralong organic afterglow from small molecular host-guest materials: State of the art

Ultralong organic afterglow materials are being actively explored as attractive candidates for a wide range of applications such as data storage, security inks, emergency lighting, etc., due to their unique long-lived excited state properties and inherent advantages of low cost, appreciable functionality and ease of preparation. To break through the core bottleneck of low luminescence efficiency and poor environmental stability of pure organic materials, the host-guest doping strategy has been widely applied in recent years. This strategy uniformly disperses luminescent small molecules (guests) in a specific small molecule host matrix and regulates the excited state dynamics of the guest molecules through non-covalent interactions (such as hydrogen bonds, π-π stacking, van der Waals forces) between the host and guest molecules, constructing ultralong organic afterglow host-guest materials. Among them, organic small molecules, due to their ability to undergo precise chemical modification to adjust the electronic structure and optimize intermolecular interactions, are expected to become ideal materials for precise control of afterglow color, lifetime, and stimulus response behaviors.

 

Over the past few years, researchers have conducted in-depth studies in the field of host-guest type organic long afterglow small molecule materials. From molecular structure design such as constructing rigid planar skeletons and introducing steric hindrance groups to the regulation of aggregated states such as constructing supramolecular assemblies, the research dimensions have been continuously expanded. Pure organic small molecule crystal materials, amorphous thin film materials and other forms of long-life luminescence have been achieved successively. However, there is still a lack of review studies on how to systematically achieve efficient and ultra-long organic afterglow from small molecule host-guest materials. Existing reviews mostly focuses on the performance optimization or mechanism exploration of host-guest type organic ultra-long afterglow materials based on polymer substrates, lacking a systematic review of core issues such as the selection principles of host-guest in small molecule systems and strategies for efficiency improvement. This makes it difficult for researchers to draw on mature experiences when designing new systems.

 

IIn this review study, the research team closely follows the cutting-edge developments in this field over the past three years (2022-2025), focusing on host-guest type ultralong afterglow materials constructed based on organic molecules. The research team classified the covered materials into URTP materials, UTADF materials and OLPL materials based on special structures such as charge transfer complexes according to different excited state transition mechanisms. The review  provides a detailed introduction and evaluation of typical research works based on each luminescence mechanism. Additionally, it conducts a comparative analysis of the photophysical properties such as doping ratio, material state, afterglow wavelength, afterglow lifetime, and quantum efficiency of different types of host-guest type organic molecular ultra-long afterglow materials.

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