Article pubs.acs.org/Langmuir
Novel PPV/Mesoporous Organosilica Composites: Influence of the Host Chirality on a Conjugated Polymer Guest S. Hessam M. Mehr,† Michael Giese,† Hao Qi,† Kevin E. Shopsowitz,† Wadood Y. Hamad,‡ and Mark J. MacLachlan*,† †
Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, V6T 1Z1, Canada FPInnovations, 3800 Wesbrook Mall, Vancouver, British Columbia, V6S 2L9, Canada
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S Supporting Information *
ABSTRACT: The conjugated polymer poly(p-phenylenevinylene) (PPV) was polymerized in the pores of chiral nematic mesoporous organosilica to give a composite film showing the strong characteristic fluorescence of PPV as well as the iridescence due to the photonic band gap of the host material. Detailed circular dichroism (CD) studies reveal a chiral structure of the polymer within the pores. These new fluorescent materials undergo fluorescence quenching upon exposure to electron deficient aromatics such as 2,4,6-trinitrotoluene (TNT), indicating that they may be useful for developing chemical sensors.
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behavior and optical properties.24 Therefore, several attempts and methods have been developed for macroscopic alignment of the usually randomly orientated polymer fibrils.25−31 A molecular approach to align conjugated polymers is to attach asymmetric side groups to the conjugated polymers, which leads to macroscopic chirality of the polymer chains.32,33 Conjugated polymers with helical conformations may offer new opportunities in ferroelectric materials and nonlinear optics. In 1998, Akagi et al. demonstrated that polyacetylene formed in a chiral nematic liquid crystal adopts a spiraling helical structure.34−36 This concept of using an asymmetric reaction solvent has been extended to induce chiral conformations in other conjugated polymers.37,38 Other approaches to introduce asymmetry into conjugated polymers in order to achieve optical activity have also been reported.24 Recently our group reported a simple approach to mesoporous silica and organosilica films exhibiting chiral nematic order.39,40 The chiral nematic materials were obtained by using cellulose nanocrystals (CNCs) as a template. Upon subsequent removal of CNCs from the composites, chiral nematic mesoporous silica (CNMS) films with interesting optical properties for applications in sensing and selective filters are obtained. We also investigated the ability of CNMS to act as a template in the preparation of chiral nematic mesoporous carbon41 and the introduction of chirality into silver nanoparticle assemblies in the pores of the CNMS.42 Templating the
INTRODUCTION The conjugated organic polymer poly(p-phenylenevinylene) (PPV)1 has attracted considerable attention due to its potential use in a variety of applications such as organic electronics,2−5 chemosensors,6,7 lasers,8,9 or nanocomposite materials.10−12 However, the performance of the PPV devices under ambient conditions suffers from gradual degradation of the polymer by reaction with moisture or oxygen. A viable method to prevent the degradation of PPV is the encapsulation of the polymer in microporous (pore size
