Near Infrared (NIR) imaging agents are extensively used in the biological or preclinical treatment and diagnosis of a wide range of diseases including cancers and tumors. The current arsenal of NIR compounds are most constituted by organic dyes, polymers, inorganic nanomaterials, whereas Ln molecular complexes explore an alternative approach to design NIR probes that are potentially bring new molecular toolkits into the biomedicine. In this review, NIR imaging agents are categorized according to their molecular sizes, constitution and the key properties and features of each class of compounds are briefly defined wherever possible. To better elucidate the features of Ln complexes, we provide a succinct understanding of sensitization process and molecular Ln luminescence at a mechanistic level, which may help to deliver new insights to design NIR imaging probes. Finally, we used our work on NIR ytterbium (Yb³⁺) probes as an example to raise awareness of exploring biologically relevant chemical space for lanthanide complexes as chemical entities for biological activity.

近红外（NIR）显像剂广泛用于生物学或临床前治疗和诊断多种疾病，包括癌症和肿瘤。当前的NIR化合物库主要由有机染料，聚合物，无机纳米材料组成，而Ln分子复合物探索了一种替代方法来设计NIR探针，这有可能为生物医学带来新的分子工具包。在这篇综述中，NIR成像剂根据其分子大小，组成进行了分类，并尽可能简要地定义了每类化合物的关键特性和特征。为了更好地阐明Ln配合物的特征，我们从机械的角度简要了解了敏化过程和分子Ln发光，这可能有助于为设计NIR成像探头提供新的见解。最后，我们在NIR（（Yb³⁺）探针为例，以提高人们对探索镧系元素络合物作为生物活性化学实体的生物学相关化学空间的认识。