Chemical Events in Oligo(3-methoxythiophene) Coating Solutions and Their Effect on the Goldlike Coating Film Properties

Abstract

Metal-free, metal-like lustrous films may find applications in a variety of fields, and a study of the factors affecting their stability is highly desirable. In particular, chemical events occurring in the coating solutions might affect the supramolecular organization of the films and therefore the metal-like luster. Herein, the chemical events occurring in acetonitrile and nitromethane coating solutions of oligo(3-methoxythiophene) and their effect on the optical properties of the films were investigated by X-ray diffraction, UV-vis absorption, and viscosity measurements. In acetonitrile, the oligomers underwent gradual dedoping with time, but only small changes in viscosity were observed. The solution was applied to a glass plate to yield a dark brown film, which turned into a goldlike lustrous film by rubbing. In nitromethane, the supramolecular structure of the oligomers changed with time from the nonaggregated state to π-dimers and then to π-stacks, and the viscosity increased. The properties of the goldlike films prepared from this solution were greatly affected by this chemical event. Remarkably, the π-dimer solution provided the film with the highest specular reflectance, yellowness, greenness, brightness, and crystallinity.

Oligo(3-methoxythiophene)s as Water-Soluble Dyes for Highly Lustrous Gold- and Bronze-like Metal-Effect Coatings and Printings

“…The differences in color between films 1 and 2 can be attributed to differences in the effective conjugation lengths of oligomers 1 and 2 (see Figure S6, Supporting Information). Focusing on the maximum reflectance, the reflectance of both films 1 and 2 (28 and 40%, respectively) significantly exceeds the reflectance of film 3 (18%), , also exceeding that of previously reported metal-free organic gloss films or aggregates (11–22%). − Also, the excellent reflectance of both films 1 and 2 is comparable to the reflectance of coating films cured from metal-effect pigments. , …”

“…To find the cause of the high luster property, we conducted specular reflectance measurements, color measurements, ellipsometry measurements, and surface roughness measurements on both films 1 and 2. The specular reflection spectra of films 1 and 2 are shown in Figure a; the spectrum , of film 3 and both evaporated metallic gold and copper films (200 nm thick) are also shown for comparison (Figure b). Films 1 and 3 strongly reflected yellow light (570–590 nm), orange light (590–620 nm), and red light (620–750 nm) yet only slightly reflected green light (495–570 nm).…”

“…Recently, it was shown that a ClO 4 – -doped 3-methoxythiophene oligomer produced gold-like lustrous films while satisfying all of the aforementioned desiderata. − This oligomer is possibly the first nonmetallic material that is likely to be used during the industrial production of lustrous inks and paintings. However, the oligomer was solvated in either nitromethane or acetonitrile that are considered to be employee-unsafe. , Typically, solvents deemed suitable for employee-safe environments are preferred for use (e.g., water).…”

“…To date, poly­(3-alkylthiophene) molecules, with an alkyl group bound to the 3-position of the thiophene ring, have displayed self-organizing properties, capable of forming lamellar crystal structures, attributed to intermolecular interactions. This unique self-orientating property is promising for use in applied organic electronics devices. − The aforementioned 3-methoxythiophene oligomer also forms self-organizing lamellar crystal structures similar to those of poly­(3-alkylthiophene), which have been studied extensively. − However, this oligomer displays specific properties arising from compactness of the methoxy group, high levels of electron donation, and multiple supramolecular interaction points; the oligomer shows specific morphological, optical, and chemical properties different from those of poly­(3-alkylthiophene). For example, the former has larger optical constants (refractive index and extinction coefficient) than the latter. , …”

Stimuli-Responsive Biomimetic Metallic Luster Films Using Dye Absorption and Specular Reflection from Layered Microcrystals

“…However, conventional metallic luster paints contain metal flakes, such as aluminum and zinc, which often pollute the environment. − To overcome these problems, attention has been directed to the preparation of metallic luster materials using metal-free organic compounds. The fabrication of metallic luster materials has been reported using various organic compounds, including thiophene, − pyrrole, aniline, porphyrin, and thiadiazol derivatives . One of the present authors has also reported the preparation of metallic luster materials using azobenzene derivatives.…”