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Ultrathin gold films, with thicknesses between the onset of conductivity (d ∼ 5 nm) and the electron mean free path (d ∼ 80 nm), display surface-sensitive resistivities, which have been exploited to follow the adsorption and desorption of molecular monolayers at the metal-solution interface with high precision. For nominal Au film thicknesses (d ∼ 40 nm), strongly chemisorbed thiolate monolayers increase the resistivity of the thin Au films by ∼4%, but weakly adsorbed species, such as pyridine or phenolate at open circuit, induce no observable change in the Au film resistance. Resistivity measurements implemented with a high-stability current source and high-precision digital voltmeter sampling at 1 Hz resulted in 3σ uncertainties in alkanethiolate coverage of 1.4 × 10(-)(4) monolayer. Surface plasmon resonance measurements, performed simultaneously with resistivity measurements, indicate that changes in resistivity vary monotonically with coverage with three distinct regions:  a low-coverage region of heightened adsorbate mobility, an intermediate-coverage region with generally linear behavior, and a chain length-dependent saturation region at high coverages. Resistivity measurements were also capable of reproducibly following the chemical state of the Au surface through a complex set of redox manipulations, demonstrating the versatility of this simple measurement.

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The ultraviolet (UV)-photoinduced chemistry at low irradiances in O 2 and the O 3 thermal chemistry of alkanethiolate SAMs have been studied. At the low irradiances typical of lowpressure Hg lamps, UV photolytic generation of products soluble in polar solvents from hexadecanethiol (HDT) SAMs requires both O 2 and irradiation below 200 nm. Significantly, exposure of HDT SAMs to ex situ generated O 3 in the dark produced the same results as UV irradiation of HDT SAMs in the presence of O 2 . Both of these facts suggest a leading role for photogenerated O 3 in the UV photochemistry of alkanethiol SAMs. Further, O 3 was found to be at least an order of magnitude more effective than other active oxygen-containing species at generating labile products under the conditions employed. The products of reaction from either O 3 exposure or UV irradiation in O 2 appear to be oxidized sulfur headgroups, which are easily removed by subsequent rinsing in a polar solvent. The heterogeneous reaction of O 3 with alkanethiols is remarkably efficient with one oxidation event occurring for every 3300 O 3 molecules transiting the flow cell. Finally oxidation at the S atom dominates reactions in the interior of the film under the conditions used. Taken together, these results are convincing evidence that UV photooxidation of HDT SAMs at low irradiances proceeds principally by generation of O 3 followed by ozonolysis of the sulfur headgroup to produce solvent-labile species which can be subsequently removed.

Two methoxy-substituted tetraphenylethylene (TPE) derivatives, tetra(4-methoxyphenyl)ethylene (TMOE) and tetra(3,4-dimethoxyphenyl)ethylene (TDMOE), were synthesized by McMurry reaction in high yields.The nearly centrosymmetric and natural propeller shape of TMOE and TDMOE excluded intermolecular effects, such as H or J-aggregation and p-p stacking, on their AIE (AIEE) and mechanofluorochromic performance. The crystal structures of TMOE and TDMOE, and theoretical calculations proved that their emission colours are determined by single molecular conjugation. These molecules were used to investigate pure conformational effects on molecular emissions. The spectral properties of these molecules in five environments of crystal(s), THF solution, THF-water binary solution, solidified THF and amorphous states, were investigated. The crystalline to amorphous phase transition by grinding resulted in good mechanofluorochromic performances with high quantum yields and distinguishable emission change, which was further explored as anti-counterfeiting inks on banknotes.