<div>Aggregation in carbon dots</div><div>Yi Ru, Geoffrey I. N. Waterhouse, Siyu Lu*</div><div>Dr. Yi Ru, Prof. Siyu Lu</div><div>Green Catalysis Center, and College of Chemistry, Zhengzhou University,
Zhengzhou 450000, China.
E-mail: sylu2013@zzu.edu.cn</div><div>Prof. Geoffrey I. N. Waterhouse
School of Chemical Sciences, The University of Auckland, Auckland 1142,
New Zealand.</div><div>Keywords: carbon dots, aggregation, special morphology, special
luminescence, special application</div><div>Carbon dots (CDs) possess
outstanding luminescence properties, making them widely used in optical
displays, anti-counterfeiting systems, bioimaging and sensors.
Presently, there is much debate about the classification of CDs, as well
as their formation process, structure and fluorescence mechanisms.
Aggregation plays an important role in the formation and fluorescence
(e.g. aggregation-induced emission) of CDs, yet is seldom studied in
detail. This review aims fill this knowledge gap, by firstly exploring
how aggregation leads to the formation of different types of CDs (e.g.
graphene quantum dots, carbon quantum dots, and carbonized polymer
dots), followed by a detailed examination of the effect of
aggregation-induced morphology on the luminescence properties and
application of CDs. Finally, opportunities and challenges for the
application of CDs in various applications are discussed, with the need
for better mechanistic understanding of aggregation-induced luminescence
being an imperative.</div><div>Introduction</div><div>The development of fluorescent nanomaterials has driven innovation in
many fields, including photoelectric devices, bioimaging, biomedicine,
sensing, and many other areas.<sup>[1-5]</sup> Unlike
conventional aggregation-induced quenching in molecules, many
fluorescent nanomaterials show negligible emission at low concentrations
but emit intensely in the aggregated state. Aggregation-induced emission
was first proposed by Tang et al. <sup>[6]</sup> in 2001.
Aggregation-induced emission is now being exploited in chemical sensing,
environmental monitoring, biological imaging, optoelectronic devices,
medical diagnosis and treatment, amongst other
applications.<sup>[7-9]</sup> This has motivated research
aimed at better understanding of the luminescence of
aggregates,<sup>[10]</sup> with innovative mechanisms
proposed to account for different emission phenomena, including
clusterization-triggered emission, through-space interactions, and so
forth.<sup>[11, 12]</sup></div>