Construction of CdS quantum dots via a regioselective dendritic functionalized cellulose template { Seok-Ho Hwang, a Charles N. Moorefield, b Pingshan Wang, a Kwang-Un Jeong, a Stephen Z. D. Cheng, a Kishore K. Kotta a and George R. Newkome* a Received (in Austin, TX, USA) 25th May 2006, Accepted 19th June 2006 First published as an Advance Article on the web 11th July 2006 DOI: 10.1039/b607352b Using regioselective dendritic functionalized cellulose, CdS quantum dot nanoparticles were prepared and their photo- optical properties and morphology as well as the preliminary biocompatibility of the hybrid were investigated. Cellulose is a polydisperse, linear chiral homopolymer consisting of regio- and enantio-selective b-1,4-glycosidic linked D-glucose units. 1 Although it contains three different hydroxyl groups at the C-2, C-3, and C-6 positions, hindered dendrons possessing a focal isocyanate moiety were shown to react exclusively at the primary hydroxyl C-6 positions. Therefore, regioselective function- alization of cellulose, i.e. the introduction of either a substituent or more than one substituent onto the cellulose chain at specific hydroxyl group(s), has led to precisely modified cellulose materials possessing new properties differing from those derived from simple statistical substitution. 2 Regiocontrol of cellulose substitution leads to the design of advanced materials and nano-scale architectures in interdisciplinary research at the interface of organic and supra- molecular chemistry. Utilitarian applications of this chemistry include liquid crystalline polymers, 3,4 host–guest assemblies, 5,6 sensor matrices, 7,8 and bioactive materials. 9–11 Semiconductor nanocrystals and quantum dots (QDs) have also attracted great interest from the biological and medical commu- nities. 12–18 Compared with conventional organic fluorophores (e.g., typical organic chromophores), QDs have high luminescence (e.g., 1 QD 5 10 to 20 fluorophores), high resistance to photobleaching, narrow spectral line widths, and tunable emissions that can be excited using a single wavelength. 19,20 However, there are a few major considerations in using these nanoparticles in a biological setting, e.g., the aqueous solubility and biocompatibility required for biological applications. To preliminarily explore the biocompatibility of quantum dot nanoparticles, we herein describe the preparation of dendrimer- stabilized CdS quantum dots attached to the cellulose main chain modified by regioselective functionalization. 21,22 Their photo- optical properties as well as morphology are examined. As previously reported, the reaction of isocyanate-based dendrons proceeds regioselectively to functionalize the primary alcohol positions 23 and their reaction with secondary and tertiary hydroxyl groups was exceedingly slow or non-existent, respectively. Treatment of cellulose with a 3rd generation isocyanate-based dendron 24 thus gave the dendrimerized cellulose polycarbamate. The strategy for the preparation of modified cellulose/CdS composites is illustrated in Scheme 1. The terminal ester groups of the dendronized cellulose 1 were cleaved using formic acid at 25 uC to generate the {[(HO 2 C) 27 -Den]-cellulose} 2. Preparation of the CdS quantum dots with {[(HO 2 C) 27 - Den]-cellulose} is similar to that of dendrimer-templated nano- particles. 25 CdS/cellulose hybrid 3 was prepared by alternating a Departments of Polymer Science and Chemistry, The University of Akron, Akron, OH 44325-3909, USA. E-mail: newkome@uakron.edu b Maurice Morton Institute of Polymer Science, The University of Akron, Akron, OH 44325-3909, USA { Electronic supplementary information (ESI) available: Detailed experi- mental procedure for biocompatibility test and photograph. See DOI: 10.1039/b607352b Scheme 1 Reagents and conditions: (i) G3-NCO dendron, dibutyltin dilaurate, LiCl, DMAc, 60 uC; (ii) HCO 2 H, 25 uC; (iii) Cd(NO 3 ) 2 ?4H 2 O, Na 2 S, MeOH. COMMUNICATION www.rsc.org/chemcomm | ChemComm This journal is ß The Royal Society of Chemistry 2006 Chem. Commun., 2006, 3495–3497 | 3495