Mark D. Mowery

The synthesis of conjugated diacetylene monomers for the fabrication of polymerized monolayer assemblies

Abstract Symmetrical disulfides containing conjugated diacetylene groups for use in forming polymerized self-assembled monolayers have been fabricated using common synthetic techniques. In contrast with previous reports, the proposed synthetic route does not require the use of hexamethylphosphoramide (HMPA) or the incorporation of an ester moiety near the surface attachment site. Overall yields of 20–30% are readily achieved for this four-step synthesis.

Fabrication of Extended Conjugation Length Polymers within Diacetylene Monolayers on Au Surfaces: Influence of UV Exposure Time

The effective conjugation length of the delocalized polymer backbone is one of the key factors in designing monolayer polymers for sensor or nonlinear optical applications. In this manuscript, the photopolymerization behavior of self-assembled diacetylene-containing disulfide monolayers is assessed on gold surfaces. Formation of the long conjugation length, so-called blue form, of the polydiacetylene backbone structure is exclusively monitored using resonance Raman spectroscopy as a function of UV exposure time. In these studies, initial formation of the blue polymer form is followed by an irreversible loss with prolonged exposure. This behavior mirrors the chromatic phase transition to shorter conjugation lengths exhibited for multilayer Langmuir−Blodgett films upon extended UV exposure. Although the exact nature of this phase transition remains elusive, most theories focus on factors affecting the alignment of the polymer backbone and influencing the effective conjugation length. Three such factors are ...

Dual-Wavelength Resonance Raman Spectroscopy of Polydiacetylene Monolayers on Au Surfaces

In this paper, resonance Raman spectroscopy with dual-wavelength laser excitation is applied to study the chromatic phase properties of self-assembled diacetylene monolayers on atomically flat Au surfaces. Laser excitation at 632.8 nm is utilized to exclusively monitor the longer conjugation length blue-phase polydiacetylene (PDA) backbone structure, while laser excitation at 514.5 nm is applied to probe the shorter conjugation length red phase. This experimental design allows in situ measurement of the photophysics and chemistry of the polymerization process within a single molecular layer. These studies demonstrate the presence of multiple chromatic species of PDAs within the same monolayer structure. Similar to observations for analogous thin film and multilayer assemblies, systematic conversion from the higher conjugation length blue form of the polymer to the shorter conjugation length red form is observed upon extended UV irradiation. Moreover, a very large Raman dispersion of 130 cm−1/eV is measured, demonstrating the highly conjugated nature of these monolayer polymers. Finally, backbone planarity and strain during the polymerization process are assessed by using the correlation of double- and triple-bond stretching frequencies.

Nanometer-scale design and fabrication of polymer interfaces using polydiacetylene monolayers

The incorporation of photopolymerizable diacetylene structures within spontaneously organized monolayers has facilitated the fabrication of robust interfacial assemblies with covalent molecular scaffolding. Through selective ultraviolet-induced polymerization, the resulting polydiacetylene monolayers permit precise structural control in the lateral domain through phototemplating. Results presented in this article demonstrate that these unique monolayer polymers also allow control of the vertical domain within the monolayer through variation of the conjugated polymer backbone position along the length of the alkyl chains. Small variations in the vertical position of the diacetylene groups of less than a nanometer are found to have a profound impact on both polymerization efficiency and the resulting conjugation length of the polymer interface. Furthermore, the relative position of this polymer backbone within the alkyl chains can be utilized to manipulate the overall properties of the assembly such as the ...