Aggregation in carbon dots
Yi Ru, Geoffrey I. N. Waterhouse, Siyu Lu*
Dr. Yi Ru, Prof. Siyu Lu
Green Catalysis Center, and College of Chemistry, Zhengzhou University, Zhengzhou 450000, China. E-mail: sylu2013@zzu.edu.cn
Prof. Geoffrey I. N. Waterhouse School of Chemical Sciences, The University of Auckland, Auckland 1142, New Zealand.
Keywords: carbon dots, aggregation, special morphology, special luminescence, special application
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.
Introduction
The development of fluorescent nanomaterials has driven innovation in many fields, including photoelectric devices, bioimaging, biomedicine, sensing, and many other areas.[1-5] 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. [6] 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.[7-9] This has motivated research aimed at better understanding of the luminescence of aggregates,[10] with innovative mechanisms proposed to account for different emission phenomena, including clusterization-triggered emission, through-space interactions, and so forth.[11, 12]