Key Takeaways & Executive Findings
- •• • Construction strategies for Ch-CDs are systematically categorized into one-step synthesis, surface modification, and assembly methods, enabling tailored design for specific applications. • • Tunable multicolor CPL has been achieved in Ch-CDs, with emission wavelengths spanning the visible spectrum, facilitating applications in displays and anti-counterfeiting. • • CPL enhancement strategies have yielded dissymmetry factors (glum) up to 10^-2, critical for chiroptical device performance. • • Triplet-state emission in Ch-CDs enables room-temperature phosphorescence with lifetimes exceeding 1 second, opening avenues in bioimaging and security inks.
Abstract
Chirality is a fundamental property ubiquitous in nature, playing a pivotal role across physics, chemistry, biology, and materials science. With the advent of nanotechnology, chiral research has extended to the nanoscale, where chiral quantum dots have attracted attention due to high photoluminescence quantum yields and stability. However, conventional II–VI quantum dots often contain toxic heavy metals, exhibit poor water solubility and biocompatibility, and require complex preparation. Carbon dots (CDs), a novel class of carbon-based nanomaterials under 10 nm, offer low toxicity, straightforward synthesis, and excellent biocompatibility. Chiral carbon dots (Ch-CDs) combine the advantages of CDs with intrinsic chirality, endowing them with circularly polarized luminescence (CPL) and distinctive photophysical and chemical properties. This review systematically refines and summarizes construction strategies for Ch-CDs, including one-step synthesis, surface modification, and assembly methods. It comprehensively elaborates on recent advances in optical properties, focusing on tunable multicolor CPL, CPL enhancement, and triplet-state emission, addressing a gap in reviews on triplet-related chiral functionalities. The challenges and future perspectives for diversified applications are proposed. Ch-CDs have been extensively applied in photoelectric detection, optical devices, biomedicine, information anti-counterfeiting, and encryption. This review aims to summarize current achievements and stimulate further research, fostering rapid development in the Ch-CDs field.
1. Introduction
Conventional chiral quantum dots, particularly II–VI semiconductors, suffer from intrinsic limitations: they frequently incorporate toxic heavy metals such as cadmium and lead, exhibit poor water solubility and biocompatibility, and demand intricate preparation protocols. These drawbacks impede their translation into biomedical and environmental applications, where non-toxicity and stability are paramount. The search for alternative chiral nanomaterials that are benign, easily functionalized, and scalable has thus become a critical research frontier.
Carbon dots (CDs) emerge as a compelling substitute, offering low toxicity, straightforward synthesis from abundant precursors, and excellent biocompatibility. By imparting chirality to CDs, chiral carbon dots (Ch-CDs) inherit these advantages while gaining circularly polarized luminescence (CPL) and unique chiroptical properties. This review addresses the gap in systematic coverage of Ch-CDs, particularly focusing on construction strategies and optical characteristics including triplet-state emission. The experimental protocols detailed herein provide a roadmap for fabricating Ch-CDs with controlled chirality and enhanced CPL, directly tackling the bottlenecks of toxicity and complex processing that have hindered conventional quantum dots.
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Suya Liu, Jiping Xiao, Wenjuan Xiang, Lin Ai, Siyu Lu (2026). Advances in the construction, optical characteristics, and applications of chiral carbon dots. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3938-0
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Frequently Asked Questions
What are the primary construction strategies for chiral carbon dots, and how do they influence the dissymmetry factor (glum) and emission wavelength?
The review categorizes construction into one-step synthesis, surface modification, and assembly. One-step synthesis often yields Ch-CDs with intrinsic chirality, but glum values are typically low (10^-3). Surface modification with chiral ligands can enhance glum to 10^-2, while assembly into helical structures can further amplify CPL. Emission wavelength is tunable by controlling carbonization temperature and surface functional groups, enabling multicolor emission from blue to red.
How do chiral carbon dots achieve room-temperature phosphorescence, and what are the typical lifetimes and quantum yields?
Triplet-state emission in Ch-CDs is achieved by promoting intersystem crossing through heavy-atom effects or coupling with matrices like g-C3N4. Lifetimes can exceed 1 second, as demonstrated in ultralong-lived triplet excitons, with phosphorescence quantum yields reaching up to 20% in optimized composites. These properties are essential for anti-counterfeiting and bioimaging applications.
What are the main challenges in scaling up the production of chiral carbon dots for commercial applications?
Scalability is hindered by batch-to-batch reproducibility in chirality and optical properties. The synthesis often relies on hydrothermal or microwave methods that require precise control of temperature and precursor ratios. Additionally, achieving high glum values consistently remains difficult. Future efforts must focus on standardized protocols and robust chiral inducers to ensure industrial viability.
How do chiral carbon dots compare to traditional chiral quantum dots in terms of toxicity and biocompatibility for biomedical use?
Ch-CDs are composed primarily of carbon, hydrogen, oxygen, and nitrogen, eliminating toxic heavy metals. In vitro and in vivo studies indicate low cytotoxicity and excellent biocompatibility, with cell viability >90% at concentrations up to 200 μg/mL. This contrasts with Cd-based quantum dots, which exhibit significant toxicity. Ch-CDs also show good water solubility and can be functionalized for targeted delivery.
What specific applications in information encryption and anti-counterfeiting have been demonstrated using chiral carbon dots?
Ch-CDs with CPL properties enable encryption through polarization states, which are difficult to counterfeit. For example, films with circularly polarized long afterglow have been used to create multi-level security codes. The combination of color and polarization provides an additional dimension for data storage. In one study, visible-light-excited full-color phosphorescent CDs were applied to anti-counterfeiting patterns, demonstrating high security and easy verification.
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