Electrophoretic and Photolithographic Fluorescent Imaging with t-BOC-Protected Poly(t-BQzMA)-Polyaniline Conducting Particle System

Abstract

Figure 2. SEM (a), photographs of the conducting particles (ca. 0.5 μm) without irradiation (b) and upon 365 nm irradiation (c). Among the conducting polymer, polyaniline-based photoimages are important since the conducting properties of polyaniline can be regulated by employing acid/base (doping/ dedoping) chemistry. Recently, we reported on noble construction of electrophoretic fluorescence imaging prepared by nano-porous particles of polyaniline-fluorescein complex. These conducting particle system hold promise as fluorophores since they are partially polarized and, as a result, they can be electrophoretically deposited onto a film of a micro-patterned polyaniline counter electrode. In continuing investigations aimed at the development of new systems for producing patterned fluorescence images, we explored the possibility of generating patterned images with conducting particles comprised of an acid-labile t-BOC group protected Qz-methacrylate polymer (t-BQzMA) and polyaniline. We hypothesized that protonation between the acidic phenol moiety of Qz polymer and a non-conducting polyaniline emeraldine base (EB) would not only render complexation but also the conductivity change of polyaniline by acid/base (doping/dedoping) chemistry. It was assumed that the partially positive-charged polyaniline emeraldine salt (ES) and negatively charged Qz polymers are separated and deposited on the counter electrode during the electrophoretic deposition process, and then patterned fluorescence images could be obtained. In order to demonstrate the feasibility of the above proposal, we developed a method to prepare micro-scale particles from the poly(t-BQzMA)-polyaniline system. A schematic of the procedure used for formation of the complex between the poly(t-BQzMA) and polyaniline is shown in Fig. 1. Polyaniline samples, poly(t-BQzMA) and t-BOC-polyaniline were prepared as described in detail elsewhere. Simply, blending the polyaniline EB and the poly(t-BQzMA) (1:2 by weight) in 1-methyl-2-pyrrolidinone (NMP) as solvent enabled the introduction of doped fluorescent labels on the porous particles as a consequence of proton transfer (or doping) under triphenylsulfonium triflate (TPSOTf, 5 wt%) as a photo acid generator (PAG); the solution was irradiated with 250 nm UV for 30 min, and then heated at 70 C for 1 h to give the deprotected phenol form from the protected Qz polymer. Since the polyaniline in its EB state is basic, acidic phenol moiety of Qz polymers can exist in phenoxy anion forms. Slow addition of NMP solution to ethanol followed by sonification leads to efficient formation of micro-scale particles. Scanning electron microscope (SEM) images, obtained following centrifugation and removal of large aggregates by filtration (1 μm), demonstrate that the micro-sized particles are indeed generated by this method (see the experimental part) as shown in Fig. 2a. An ethanol solution, containing the particles obtained from the poly(t-BQzMA) and the EB form of polyaniline, display a purple-pink (Fig. 2b) and bright yellow emission (Fig. 2c). The bright yellow emission indicates that they emit bright yellow fluorescence associated with the deprotected phenol form of poly(QzMA) and, as a result, they can be protonated to the EB form of polyaniline to give the ES form. In addition, the micro-sized particles were found to be stable as ethanol suspensions without aggregation even after heating to reflux condition for 24 h. The particles are also stable in the presence of 5% tetrabutylammonium fluoride salt. The observation of stable particles is significant in that most of conducting polymer particles probed to date tend to aggregate after prolonged storage. It is felt that the approach described above should be