We introduce an innovative and robust method for the preparation of nanocomposite multilayers, which allows accurate control over the placement of functional groups as well as the composition and dimensions of individual layers/internal structure. By employing the photocross-linkable polystyrene (PS-N(3), M(n) = 28.0 kg/mol) with 10 wt % azide groups (-N(3)) for host polymer and/or the PS-N(3)-SH (M(n) = 6.5 kg/mol) with azide and thiol (-SH) groups for capping ligands of inorganic nanoparticles, nanocomposite multilayers were prepared by an efficient photocross-linking layer-by-layer process, without perturbing underlying layers and nanostructures. The thickness of individual layers could be controlled from a few to hundreds of nanometers producing highly ordered internal structure, and the resulting nanocomposite multilayers, consisting of polymer and inorganic nanoparticles (CdSe@ZnS, Au, and Pt), exhibit a variety of interesting physical properties. These include prolonged photoluminescent durability, facile color tuning, and the ability to prepare functional free-standing films that can have the one-dimensional photonic band gap and furthermore be patterned by photolithography. This robust and tailored method opens a new route for the design of functional film devices based on nanocomposite multilayers.

Layer-by-layer (LbL) self-assembly is a versatile and simple methodology for growing polymer and polymer/inorganic nanoparticle hybrid multilayer thin films with controlled chemical composition and thickness on the nanometer scale. [1] Traditional LbL assembly is carried out in aqueous media and is based on the electrostatic attraction between two oppositely charged materials, such as polycations and polyanions. The recent progress in utilizing hydrogen bonding, click chemistry, disulfide bonding, silanization, esterification, urethane linking, amidation, and so forth, for LbL self-assembly has allowed the growth of multilayer thin films in polar solvents, mainly water and/or alcohols.[2] To our knowledge, LbL self-assembly for functional organic/inorganic nanocomposites has not yet been implemented in nonpolar solvents. Herein we report the first success in using a nucleophilic substitution reaction for LbL self-assembly of organic/inorganic multilayers in nonpolar solvents. Based on a nucleophilic substitution reaction between Br and NH 2 , alternating layers of highly hydrophobic CdSe@ZnS quantum dots (QDs) capped with 2-bromo-2-methylpropionic acid (BMPA) in toluene or hexane and poly(amidoamine) dendrimer (PAMA) in ethanol were deposited to form QD/ PAMA composite multilayer thin films. The resulting thin films exhibited more robust photoluminescence (PL) in air (oxidation) and in the presence of moisture (hydrolysis) than those obtained by electrostatic LbL self-assembly. These results also demonstrate the possibility of LbL growth of patterned films based on nucleophilic substitution with the aid of microcontact printing.Photoluminescent (and electroluminescent) polymer/QD nanocomposite films are quite important in technical applications and may be used as functional components in electronic devices, such as optical thin films, or for biomedical imaging. [3][4][5][6][7][8] Nevertheless, there has been limited success in fabricating polymer/QD composite thin films using the LbL self-assembly techniques developed to date, because the PL properties of the embedded QDs are usually poor. Conventional LbL self-assembly techniques are carried out in aqueous or polar media, which means that the QDs, which are produced either directly in aqueous or polar media or obtained through ligand exchange or phase transfer, have poor surface passivation, which makes the PL of the resulting QDs vulnerable either during LbL self-assembly or during the thin film storage. Recent studies have shown that a high packing density of small and hydrophilic thiol ligands reduces the quantum yield of QDs significantly. [9,13] Kotov et al. reported that the PL intensity of composite multilayer thin films of polyelectrolyte and citrate-stabilized CdSe@CdS QDs was increased by 50-500 times after ambient light irradiation for several days owing to surface oxidization on the QDs with ambient oxygen for 3 days, [11] which was accompanied by a notable blue shift in the PL bands with exposure time. To date, the growth of polymer/QD multilayer...