Structural Transitions in Polydiacetylene Langmuir Films

Abstract

Polydiacetylene (PDA) Langmuir films (LFs) were investigated directly at the air/water interface using in situ synchrotron grazing incidence X-ray diffraction, and ex situ transmissison electron microscopy and diffraction. The films were compressed and polymerized on pure water. A crystallographic model describes the structures and phase transitions of the unpolymerized (monomer) film, via the metastable (blue phase), to the fully stable PDA red phase as a function of irradiation dose. The monomer-to-blue-to-red chromatic phase transitions are accompanied by changes in the in-plane crystal structure and pendant chains packing arrangement from arced alkyl chains (in the monomer and blue phases) to near-vertical closely packed chains in the red phase. Notably, the characteristic linear strand morphology of PDA films can be explained as a direct result of the marked decrease in spacing between adjacent polymer chains upon transition from the blue to the red phase.

Roles of head group architecture and side chain length on colorimetric response of polydiacetylene vesicles to temperature, ethanol and pH

“…The color transition takes place when the thermal motion of all segments overcome inter-and intra-chain interactions within the PDA vesicles, resulting in significant segmental rearrangement and the relief of strain in conjugated backbone [38][39][40][41][42][43]. These processes cause an abrupt increase of HOMO-LUMO energy gap.…”

“…The PDA vesicles can exist in different forms, depending on the arrangement of their segments [38][39][40][41]. In general, the unperturbed PDA vesicles posses long conjugation length and exhibit a deep blue color.…”

Stable polydiacetylene/ZnO nanocomposites with two-steps reversible and irreversible thermochromism: The influence of strong surface anchoring

“…1) [1,2,4,5]. The unperturbed PDA vesicles, in which the side chains arrange in an ordered fashion, exhibit a deep blue color [1,2,30,31]. The increase of temperature promotes the dynamics of side chains, which eventually breaks the hydrogen bonds at the surface of PDA vesicles [1,5,27,32,33].…”

Controlling the reversible thermochromism of polydiacetylene/zinc oxide nanocomposites by varying alkyl chain length

“…By increasing temperature, the dynamics of all PDA segments including alkyl tail, polar head, and conjugated backbone are promoted. When the inter-and intrachain interactions within PDA assemblies are sufficiently weaken, the rearrangement of molecular segments occurs, which in turn alters the electronic state of conjugated backbone [10,27,[46][47][48][49][50]. The HOMO-LUMO energy gap of perturbed PDA is widen, resulting in the color transition from blue to purple, red, or orange.…”

“…Upon exposure to external stimuli, the PDAs change their color to purple, red, or orange, depending on the magnitude of local perturbation. The mechanism of color transition has been widely investigated by many research groups [10,[46][47][48][49][50]. It has been generally accepted that the change of molecular conformation such as side chain and backbone packing affects the electronic states of the PDA polymers, causing the change of their optical absorption properties.…”