Fabrication of Conjugated Polymer-Coated Noble-Metal Nanoprisms with High Stability and Optical Properties

Abstract

The fabrication, characterization, stability, and optical properties of conjugated polymer-coated noble-metal nanoprisms are discussed from the point of view of physical and materials chemistry. Brief overviews of the chapter 1 and 2 in this dissertation are shown below. In chapter 1, silver nanoprisms (Ag-PRs) have been expitaxially edge-coated with gold and subsequently covered fully with P3HT chains to fabricate poly(3-hexylthiophene)-grafted edge-gold-coated silver nanoprisms (P3HT@AuAg-PRs) which are miscible with organic solvents. Both absorption and emission spectra have indicated that aggregated P3HT chains are bound on the surfaces of noble-metal nanoprisms. Picosecond emission kinetic profiles have suggested that the S1 relaxation time of P3HT in P3HT@AuAg-PRs is reduced due to energy transfer to AuAg-PRs. From nanosecond transient-absorption kinetic profiles, the reduced amplitude and the increased decay time of T1 excitons in P3HT@AuAg-PRs have been measured. The surface-enhanced Raman scattering effect of P3HT@AuAg-PRs is as high as 4.6 because the sharp tips of AuAg-PRs which are maintained via gold coating serve as hot spots. The morphology deformation time of P3HT@AuAg-PRs in H2O2(aq) has been extended 48 times longer than that of Ag-PRs. In chapter 2, self-assemblies of silver nanoprisms (AgPRs) having enhanced structural stability and optical properties have been facilely coated with polypyrrole (PPy) via the in situ polymerization of pyrrole (Py) monomers that also act as an assembling agent. The degree of AgPRs assembly has been controlled by varying the concentrations of trisodium citrate dihydrate, which bind selectively to the {111} facets of AgPRs. The morphology deformation time of self-assembled AgPRs just with thin PPy coating is 7 times longer than that of PPy-free AgPRs, suggesting that PPy coating prevents the sharp tips of AgPRs from being truncated by oxidizing agents. The surface-enhanced Raman scattering effect of highly assembled and PPy-coated AgPRs becomes as high as 6.3 due to the well-maintained sharp tips of AgPRs by PPy coating, as well as numerous hot spots generated between nanoprisms.