Scalable Synthesis of Fluorescent Organic Nanodots by Block Copolymer Templating Shubo Cao, 1,2 An N. Le , 2 Aihua Chen , 1,3 Mingjiang Zhong 2 1 School of Materials Science and Engineering, Beihang University, Beijing 100191, China 2 Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06511 3 Beijing Advanced Innovation Centre for Biomedical Engineering, Beihang University, Beijing 100191, China Correspondence to: M. Zhong (E-mail: mingjiang.zhong@yale.edu); A. H. Chen (E-mail: chenaihua@buaa.edu.cn) Received 5 June 2019; Revised 3 August 2019; accepted 4 August 2019; published online 23 August 2019 DOI: 10.1002/pola.29466 KEYWORDS: bioimaging; block copolymer; fluorescence; polymer dot; self-assembly Advancements in fluorescence imaging techniques and the development of fluorescent probes have enabled scientists to gain detailed information about cellular processes and has aided in disease diagnosis. 1–3 Many fluorescent probes have been developed, such as fluorescent dyes and semiconductor quantum dots, but there is still room for improvement; the low absorptivity and poor photostability of fluorescent dyes are problematic, 4,5 while semiconductor quantum dots are potentially cytotoxic due to the presence of heavy metals. 6 Thus, there is an ongoing demand to explore metal-free, photostable fluorescent probes. Conjugated polymer dots (Pdots) and carbon dots represent two promising candidates. 7–9 Advantages of Pdots include their brightness, photostability, and nontoxicity. 2,10–13 However, synthesis of the fluorescent conjugated polymers is challenging and requires specialized monomers, and due to the hydrophobic nature of the conjugated polymers, the preparation of Pdots requires surface modification or incorporation of hydrophilic functionalities to allow for dispersibility in water for bio- imaging applications. 14–18 Furthermore, the size of the Pdots, which is critical for their targeting ability and transport through biological systems, 19–21 is difficult to finely control. Carbon dots also display bright fluorescence, are generally nontoxic, and have good photostability. 22–25 Their bright emis- sion relies on surface passivation, typically achieved through surface modification with poly(ethylene oxide) (PEO). 26,27 A drawback of carbon dots is that their synthesis can be energy- intensive, as common methods include pyrolysis and hydro- thermal carbonization, both requiring long reaction times at elevated temperatures. 28–30 This work aims to address some of the limitations in the syn- thesis of Pdots and carbon dots by introducing a method for synthesizing fluorescent organic nanodots (FONs) from a block copolymer (BCP) template. FONs represent a middle ground between Pdots and carbon dots, as their structure consists of a conjugated carbon framework derived from a polymer template. Their synthesis is scalable and involves milder thermal treatment conditions than those used to obtain carbon dots. The templating method presented here also ensures that the FONs are well dispersed in water, without the need for additional surface modification procedures. Importantly, the polymer synthesis is accomplished without the use of specialized monomers for conjugated polymers, and the size and size distribution of the FONs can be controlled readily due to the thermodynamically predominant BCP self- assembly. Polyacrylonitrile (PAN) is well known as precursor to fabri- cate carbon materials. For example, Tang and coworkers obtained carbon nanoparticles by using the BCP of poly(tert- butyl acrylate)-b-PAN. 31 However, silicon wafers were used as substrates to preserve the morphology of discrete nanoparticles during pyrolysis, which was not economic for scalable preparation. Furthermore, PAN and its BCPs can only be soluble in a narrow range of solvents with high boiling point, which limits their application. Herein, the synthetic route is based on a poly(styrene-co-acrylonitrile) (PSAN)- containing BCP, which can be soluble in many solvents with low boiling point. Previous work has shown that under ther- mal treatment at 280  C in air, the acrylonitrile (AN) units of PSAN undergo cyclization and crosslinking. 32–34 Nitrogen orig- inating from AN is simultaneously incorporated into the obtained polymer network. This nitrogen enrichment has been exploited to modify the chemical and electronic properties of these resulting partially conjugated materials, such as surface reactivity and accessibility and electronic band structures, important for electrochemical applications. 35–37 A finding that Additional supporting information may be found in the online version of this article. © 2019 Wiley Periodicals, Inc. JOURNAL OF POLYMER SCIENCE 2020, 58, 30–34 30 JOURNAL OF POLYMER SCIENCE WWW.JPOLYMSCI.ORG RAPID COMMUNICATION