Optically flat polymer films of poly(N-hexadecylpyrrole) (PHDPy) have been successfully prepared on gold electrodes modified with self-assembled monolayers of bis(ω-(N-pyrrolyl)-n-undecyl) disulfide (BPUS). During the growth of PHDPy, the surface-confined pyrroles in BPUS serve as nucleation sites for the epitaxial growth of PHDPy instead of being laterally polymerized to form polymeric monolayers. We provide visual evidence to confirm the chemical reaction between the surface-confined pyrroles and HDPy in the solution. Polymer growth on the modified and unmodified electrodes is investigated using cyclic voltammetry, optical microscopy, and scanning probe microscopy.

The electrochemical polymerization of the n-alkylpyrrole, N-hexadecylpyrrole (HDPy) to form poly(Nhexadecylpyrrole) (PHDPy) was monitored at both a bare gold electrode surface and a gold surface modified with bis(ω-(N-pyrrolyl)-n-undecyl) sulfide (BPUS). The film growth process was monitored by chronoamperometry and electrochemical quartz crystal microbalance (EQCM). Both techniques revealed that there is a fundamental difference in the nucleation and growth of the polymer films on the modified versus the unmodified electrode surface. EQCM data revealed that the PHDPy film formed on the BPUS-modified electrode was much denser and grew in a more ordered manner than that formed on the bare gold surface. The film formed on the modified electrode was also found to be more resilient than that formed on the bare gold surface, withstanding repeated cycling in an electrolyte solution. These experiments demonstrate that the surface-confined pyrrole units on the modified electrode serve as specific nucleation sites to induce long-range order in the polymer film.

A gold electrode was modified by self-assembly of bis(w-(N-pyrrolyl)-n-undecyl)disulfide (BPUS), so that the BPUS monolayer serves as nucleation sites for the subsequent growth of polypyrrole. Formation of the BPUS monolayer was monitored by electrochemical quartz crystal microbalance (EQCM). The monolayer coverage of 3.7 x 10'4 molecule/cm 2 was determined by frequency change. The BPUS monolayers were oxidized by cyclic voltammetry, and the charge was determined by integration of the area beneath the oxidative wave of the cyclic voltammogram. Reconciliation of the surface coverage as determined by frequency change and the amount of charge passed led to the n value of 1 for each pyrrole unit of the BPUS monolayer. Two mechanisms were proposed to account for this: (i) the formation of dimers upon electrochemical oxidation of the monolayer and (ii) the formation of ketone-type degradation products because of reaction with oxygen or water. The electrochemical growth of polypyrrole on the BPUS-modified and the bare gold surface was also compared using EQCM. Frequency-charge plots for growth of polypyrrole on the unmodified surface show a nonlinear relationship, indicative of three-dimensional polymer growth. On the other hand, a linear relationship is obtained for the frequency-charge plot on the BPUS-modified surface, characteristic of layer-by-layer growth.The electrical resistivity of conducting polymers can be controlled so that it can be fully insulating to highly conducting by varying the amount and type of dopants. This variability has attracted much attention from both theoretical and practical points of view in the last decade. In the realm of theory, charge transport in conducting polymers has been explained using the concepts of solitons, polarons, and bipolarons. 1 In the practical area, rechargeable batteries based on conducting polymers are promising for commercial application. 2 Conducting polymers also show photoinduced electrochromic reactions by incorporating semiconductor particles (e.g., TiO 2 ). 3 The thirdorder nonlinear optical property of T-conjugated conducting polymers suggests potential applications in photonic devices. 4 The ease of fabrication and chemical modification of conducting polymers provides an additional advantage for future devices.However, it is difficult to control the structure and homogeneity of doping of conducting polymers. Control of the structure of these materials will result not only in a better understanding of their electronic and optical properties, but also in improving the performance of these devices. Many alkyl mercaptan derivatives undergo self-assembly to form organized monolayers on metal surfaces. 5 ' 6 Alkyl and w-substituent alkyl thiols spontaneously form monolayers on gold surfaces upon immersion of Au substrates into thiol-containing solutions. The monolayers are ordered and densely packed. These findings provide a simple method for generating nucleation sites for the subsequent growth of thin films such as conducting polymers.Rubinstein and co-workers...