Enhanced emission by cross-linking in the confined domain e | Eurek alert!

image: a, Schematic of the “addition-condensation polymerization” strategy to study domain-confined CEE in CPDs. b, Diagram of the relationship between methyl groups and the internal structure of CPDs (d1: the spacing of the original backbone inside the CPDs without methyl groups. d2: the spacing of the stretched backbone inside the CPD by methyl groups. n: the amount of introduced methyl groups in the CPDs. D: the average spacing between the backbones of the CPDs). c, solid-state RTP and solution-state QY lifetimes of CPDs with different methyl group contents. d, Schematic effect of confined-domain EECs on CPD energy levels (IC: internal conversion, Abs.: absorption, Fluo.: fluorescence, Phos.: phosphorescence).
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Credit: by Songyuan Tao, Changjiang Zhou, Chunyuan Kang, Shoujun Zhu, Tanglue Feng, Shi-Tong Zhang, Zeyang Ding, Chengyu Zheng, Chunlei Xia and Bai Yang

The last decade has seen the rapid emergence of carbon-based luminescent nanomaterials (carbon dots, CDs) as they represent one of the most promising ways to achieve efficient luminescence by easy synthesis. CPDs, as an emerging subclass of DCs, are the subject of much research. One wonders then, what shines and why does it shine?

In a new article published in Light sciences and applications, a team of scientists, led by Professor Bai Yang from the State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, China, and his colleagues reported the latest research progress on the PL mechanism of CPDs in response to these two major scientific issues. They provided strong evidence for uncovering essential roles of the spatial effect in the confined domain of CPDs on PL origin. They propose confined-domain EECs and construct a well-defined CPD model system to study the influence of spatial interactions on PL based on the “addition-condensation polymerization” strategy. They polymerized acrylic acid and methylacrylic acid in varying proportions, then synthesized CPDs from the obtained copolymers and ethylenediamine using a hydrothermal method. The adjustable content of methyl groups in the copolymers was expected to result in varying degrees of steric hindrance. Such interactions from confined domain EECs have been successfully captured by experimental characterizations and confirmed by theoretical calculations. These scientists analyzed and summarized some interesting phenomena and experimental evidence, revealing the contribution of PL-confined domain EECs in DPCs:

“1) Spatial interactions and PL performance could be tuned by adjusting the steric hindrance present inside CPDs. 2) The results of the structural characterizations demonstrated that the introduction of methyl groups widened the chain spacing inside the nanoparticles. 3) The analysis of the femtosecond transient absorption spectral profiles revealed the existence and the influence of the EECs in confined domain on the energy levels. 4) Theoretical calculations proved the rationality of the conjectured luminescent units and the proposed PL mechanism. This study is the first where confined domain EECs in DPCs have been experimentally studied. These results have the potential to help understand the unique structural advantages of CPDs and fine-tune their PL properties.

“CPDs exhibiting tunable RTP lifetimes can potentially be used as smart materials to develop multi-level anti-counterfeiting technology, which is a recent area of ​​study.” they added.

“The results revealed that the confined domain CEE exerted a significant spatial influence on the PL. The “addition-condensation polymerization” strategy could be adopted to tune the properties of CPDs. Various factors, such as the type of monomer precursors, ratios of constituent monomers, and degrees of polymerization, could be fine-tuned to modulate the properties of CPDs. Thus, the synthesis of CPD can eliminate the simple choices of compounds existing at the current stage and become more targeted. Our findings have the potential to help understand the PL mechanism of CPDs and inspire new synthetic design to obtain CPDs with customized properties. scientists predict.

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