Surface-pressure-induced reversible color change of a polydiacetylene monolayer at a gas–water interface

Abstract

The photopolymerization properties and the surface pressure dependence of excitonic absorption of polydiacetylene (PDA), i.e., poly-(heptacosa-10,12-diynoic acid), are investigated by in situ reflection spectra of a monolayer at a N2 gas–water (pure water, CdCl2 aqueous solution) interface. The electronic structure of the initially appearing PDA is strongly dependent on the packing condition of diacetylene monomer, the blue- and red-form PDAs that initially appear in loose and close packing conditions, respectively. A reversible color change induced by a change in surface pressure is found for the first time in a partially polymerized PDA monolayer on pure water, in which blue and red form PDAs appear predominantly at low and high surface pressures, respectively. Further, two metastable phases, observed at wavelengths about 40 nm longer than those of the blue form, are thought to be induced by the rheological process of the substitutional sidegroups. Our results suggest that these color changes are closely related to a strain on the acetylenic backbone structure which is induced by the deformation of substitutional alkyl sidegroups.

Functional Self-Assembling Bolaamphiphilic Polydiacetylenes as Colorimetric Sensor Scaffolds

“…A widely accepted model attributes shortening of effective conjugation length to an increase in lattice strain, 27 often induced by conformational disorder of the side chains on a conjugated PDA backbone. [28][29][30] However, recent infrared spectroscopy and AFM studies of PDA films suggest that the side chains of "red phase" PDAs induced by thermal treatment are in an equally or more ordered conformation than those in "blue phase" PDAs. 7,8 A compromised explanation suggests that the alkyl side chains in the "red phase" remain in an ordered conformation, with only a slightly different packing mode from the "blue phase".…”

Glass-supported lipid/polydiacetylene films for colour sensing of membrane-active compounds

“…Following polymerization, PDA appears intense blue to the naked eye due to its conjugated ene-yne framework (Day and Ringsdorf, 1978) Furthermore, PDA systems undergo dramatic blue-red transformations induced by varied analytes and chemical processes, such as temperature elevation, ions in aqueous solutions, and increase in surface pressure (Rubner, 1986). The visible colour changes of PDA correspond to stress-induced structural transition of the conjugated polymer backbone, brought about by molecular perturbations of the pendant sidechains of the polymer (Tokura et al, 1986;Tomioka et al, 1989).…”

A review on linear and non‐linear resonance Raman spectroscopy of the conjugated system polydiacetylene

“…pressure-induced chromism. 46 These types of chromism lead to changes in the absorption and also in the Raman spectra. A number of extensive studies have been carried out, but the molecular mechanism giving rise to the chromic transition is still a controversial subject.…”