Structurally defined carbonized polymer dots with red-to-near-infrared emission and 86% quantum yield via rapid room-temperature aromatic coupling

Abstract

Long-wavelength-emitting carbonized polymer dots (CPDs) have garnered increasing interest for use in biomedical imaging, sensing, and optoelectronics applications. However, their synthesis often relies on complex precursors, harsh reaction conditions, or poorly understood formation mechanisms. Herein, we report the rapid, room-temperature synthesis of red/near-infrared (NIR) dual-emissive CPDs (RCPDs) via successive oxidative aromatic coupling of 1,3-dihydroxynaphthalene in isopropanol, catalyzed using iron nitrate and nitric acid. The resulting RCPDs exhibit two well-defined emission bands centered at approximately 610 and 750 nm. These emissions can be rationalized within a framework involving proposed molecular fluorophores based on a fused aromatic motif, represented by 1,3,7,9,11,13-hexahydroxyacenaphthyleno[1,2-b]perylene (HHAP), and their excimer states formed through π–π stacking, respectively. Remarkably, these RCPDs achieve a quantum yield of over 85%, among the highest reported for long-wavelength-emitting CPDs. The chemical structures and formation dynamics are revealed using electrospray ionization mass spectrometry at various reaction stages. Femtosecond transient absorption spectroscopy further reveals ultrafast intersystem crossing and excimer formation pathways, supported by solvatochromic analysis and theoretical simulations. Integration of the RCPDs into polymer matrices enables the fabrication of red/NIR-emitting light-emitting devices, demonstrating their practical utility. This study presents an efficient synthetic strategy for producing structurally defined, long-wavelength-emitting CPDs and provides mechanistic insights that can guide the rational design of next-generation luminescent carbon nanomaterials.