image: a, Schematic of the “addition-condensation polymerization” strategy to investigate the confined-domain CEE in CPDs. b, Schematic of the relationship between the methyl groups and the internal structure of CPDs (d1: the spacing of the original skeleton inside CPDs without methyl groups. d2: the spacing of the stretched skeleton inside CPDs by methyl groups. n: the amount of introduced methyl groups in CPDs. D: the average skeleton spacing of CPDs). c, RTP lifetimes in solid state and QYs in solution state of CPDs with different contents of methyl groups. d, Schematic effect of confined-domain CEE on the energy levels of CPDs (IC: internal conversion, Abs.: absorption, Fluo.:fluorescence, Phos.: phosphorescence). view more
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 past decade has witnessed the rapid emergence of luminescent carbon-based nanomaterial (carbon dots, CDs) as it represents one of the most promising way to achieve efficient luminescence by facile synthesis. CPDs, as a emerging subclass of CDs, are being widely investigated. One then wonders, what is shining and why is it shining?
In a new paper published in Light Science & Application, a team of scientists, led by Professor Bai Yang from State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, China, and co-workers have reported the newest research progress on the PL mechanism of CPDs in response to these two key scientific issues. They provided solid evidences to uncover the essential roles of spatial effect within the confined domain of CPDs on PL origin. They put forwards confined-domain CEE, and constructed a well-defined model system of CPDs 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, and subsequently synthesized CPDs from the obtained copolymers and ethylenediamine following a hydrothermal method. The tunable content of methyl groups in copolymers was expected to bring about varying degrees of steric hindrance. Such interactions originated from confined-domain CEE were successfully captured by experimental characterizations and confirmed by theoretical calculations. These scientists analyzed and summarized some interesting phenomena and experimental evidences, revealing the contribution of confined-domain CEE to the PL in CPDs:
“1) The spatial interactions and PL performance could be tuned by tuning the steric hindrance present in the interior of the CPDs. 2) Results from the structural characterizations demonstrated the introduction of methyl groups enlarged the spacing of chains inside nanoparticles. 3) The analysis of the femtosecond transient absorption spectral profiles revealed the existence and influence of confined-domain CEE on energy levels. 4) The theoretical calculations proved the rationality of the conjectured luminescent units and the proposed PL mechanism. This study is first where confined-domain CEE in CPDs has been experimentally studied. These results can potentially help understand the unique structural advantages of CPDs and precisely tune their PL properties.”
“CPDs exhibiting tunable RTP lifetimes can be potentially used as smart materials to develop multi-level anti-counterfeiting technology, that is a hot field of recent study.” they added.
“The results revealed that the confined-domain CEE exerted significant spatial influence on PL. The ‘addition-condensation polymerization’ strategy could be adopted to tune the properties of the CPDs. Various factors, such as the type of the monomer precursors, the ratios of the constituent monomers, and the degrees of polymerization, could be precisely tuned to modulate the properties of the CPDs. Thus, the synthesis of CPDs can eliminate the simple choices of existing compounds as the current stage, and become more targeted. Our findings can potentially help understand the PL mechanism of CPDs, and inspire a novel synthetic design to obtain CPDs with tailored properties.” the scientists forecast.
Journal
Light Science & Applications