The Intermolecular Interaction Among Ferrocenylthiolates In Self-Assembled Monolayers And Its Surface Distuguish

Self-assembled monolayers (SAMs) are highly ordered molecular structures thatformby the spontaneous adsorption of molecules on a solid surface, and are a new type oforganic ultra-thin films developed in the last three decades. Because of the good stabilityand easy preparation, SAMs have generated wide interest in the fields of theoretical study,e.g. electron transfer kinetics, membrane permeability and surface science. Its potential inthe application fields, e.g. biomimetics, chemical sensors, nonlinear optics, molecularrecognition etc. have also been widely explored. Amongst the various SAMs that can beformed, the redox active group-terminated thiolate on gold surface, particularly theferrocene-terminated SAMs, has been shown to be an excellent model for the study oflong-range electron transfer between the redox centers and the electrode surface. In thisthesis, the heterogeneity phenomenon in the single and binary ferrocenylthiolate SAMs, themodulation of the intermolecular interaction between ferrocenylthiolate molecules, and thesurface identification of the surface distribution of ferrocenylthiolate in the SAMs arestudied. The main experimental contents are as follows:1. The redox behavior of single-component FcC11S-Au SAMs that formed by theadsorption of11-fferrocenyl-1-undecanethiol (FcC11SH) on gold surface was studied. Itwas found that peak splitting phenomenon consistently exists in the CV curves, whichindicates there are two different domains of ferrocenylthiolate molecules (FcC11S-) withinthe single component FcC11S-Au SAMs. Small organic additives, nitrobenzene (NB) andoctanol (C8OH), were added into the electrolyte to perturb the redox behavior offerrocenylthiolat mlecules in these two domains. The result illustrated that when theorganic solvent was added to the aqueous electrolyte, the redox peak at lower potential,which is related to the loosely packed domains becomes narrower and higher, whichindicating that there is a decrease of repulsion forces between FcC11S-. On the other hand,the peak at the higher potential, which is related to the closely packed domains, does notchange with the addition of the organic additives in the electrolyte. By studying theintermolecular interactions, we can realize the investigation of the two domains in the FcC11S-Au SAMs.2. The ferrocenylthiolate SAMs are excellent model for study of long-range electrontransfer between the redox centers and the electrode surface. In order to reduce the impactof the electron transfer amongst neighboring ferrocenylthiolate molecules on themeasurement of electron transfer between redox centers and the electrode surface, themixed SAMs of ferrocenylthiolate and alkylthiolate are typically prepared, in which theferrocenylthiolate are assumed to be isolated from each other by the alkylthiolates. The tworepresentative methods of preparing binary FcCnS-/CmS-Au SAMs are the pre-exchangemethod and co-adsorption method. The exchange kinetics of single component FcC11S-AuSAM with C11SH molecules was studied, and a series of FcC11S-/C11S-Au SAMs withdifferent surface density of FcC11S-(ΓFc) were prepared. The binary FcC11S-/C11S-AuSAMs with a low ΓFcand has “ideal” CV curves can be prepared by both of exchange andco-adsorption method. However, it was found that the distributions of the redox centers inthe binary redox SAMs are indeed different by comparing the redox behavior of these twoFcC11S-/C11S-Au SAMs, i.e. the shape position of peaks: the pre-exchange method isassigned to the “clustered” distributed of FcC11S-with higher intermolecular repulsionforces, which is indicated by the higher formal potentials and wider redox peaks; while theco-adsorption method resulted in “separated” distribution of FcC11S-with smallerintermolecular repulsion forces, indicated from the lower formal potential and narrowerredox peaks.3. Cucurbit[7]uril host (CB[7]) is a type of host molecule that can form highly stabledinclusion complexes with ferrocene groups (Fc) in ferroceylthiolate SAMs. The redoxbehavior of ferrocene groups change after binding with CB[7] molecules, i.e. the redoxpeaks become higher and narrower, and the formal potential shifts to a higher position. Itwas found that the occurrence of host-guest binding between CB[7] and Fc depends on thesurface distribution of the FcC11S-in the binary SAM, i.e. the CB[7] tends to bind with Fcin the domains where the FcC11S-is separated from each other due to the reduced sterichindrance. In contrast, it is unfavorable for CB[7] to bind with the Fc in the clusteredFcC11S-domains. Based on the above phenomenon, the CB[7] can be applied as “probe”to distinguish the surface distribution of FcC11S-in a series of binary FcC11S-/C8S-Au SAMs.4. The gold surface will change from hydrophilic to hydrophobic after modificationwith ferrocene-terminated self-assembled monolayers, which can adsorb a thin layer oforganic solvent on its surface, e.g. nitrobenzene (NB), with micrometer thicknesses. Withthe thin-layer electrochemical (TLEC) method, we studied the redox behavior of a series ofbinary FcC11S-/C11S-Au SAM with different surface density of ferrocenylthiolate (ΓFc) inaqueous solution and organic phases. The ion-pairing effect of the FcC11S-/C11S-AuSAMs in NB thin film was then investigated. We also studied the variations of electrontransfer rate (k) and reorganization energy (λ) when the microenvironment of themonolayer was chaged from the aqueous to organic phase by TLEC method.