Recent advances in triplet-state materials: A perspective towards bioimaging and biosensing

Abstract

Triplet-state materials have become valuable tools in bioimaging and biosensing due to their unique photophysical properties. These materials are characterized by long-lived emission lifetimes, high signal-to-noise ratios, and sensitivity to changes in their microenvironment. In this review, we examine over 500 publications and critically compare 287 highly cited studies to evaluate the current landscape of organic, inorganic, and hybrid triplet-state materials. We explain the design principles and emission mechanisms of organic systems, including thermally activated delayed fluorescence emitters and metal-organic complexes, and contrast these with inorganic counterparts, such as transition metal-doped nanomaterials and lanthanide-based probes, known for their photostability and sharp emission profiles. The review also discusses hybrid materials that combine features from both domains to address limitations and enhance biomedical applications. Key areas of focus include emerging red and near-infrared triplet emitters, surface engineering for biocompatibility and targeting, and multimodal imaging integration. We address challenges such as oxygen quenching, biological safety, and targeted in vivo delivery. By presenting a comparative framework supported by quantitative and qualitative data, this work is intended to offer a valuable resource for researchers working toward the development of next-generation triplet-state materials for high-resolution bioimaging, real-time diagnostics, and theranostic applications.