Influence of Supramolecular Interaction Type on Photoresponsive Azopolymer Complexes: A Surface Relief Grating Formation Study

Abstract

The influence of the supramolecular interaction typehydrogen bonding, proton transfer, and pure ionic bondingon photoresponsive behavior, particularly surface relief grating (SRG) inscription, has been investigated using a homopolymer with an ambient temperature glass transition (T g ). To this end, poly(dimethylaminoethyl methacrylate) (PDMAEMA or PDM) of relatively high molecular weight (42K) was complexed at various azo/DM molar ratios with dimethylaminoazobenzene derivatives functionalized by hydroxyl (azoOH) or carboxylic acid (p-methyl red or azoCOOH) groups, and quaternized PDM (PDMQ) was complexed at equimolar ratio with a sulfonated analogue (methyl orange or azoSO 3 ), and the structural and thermal properties of these complexes were determined. SRG inscription on spin-coated films was found to be possible because complexation increases the T g above ambient. The efficiency of SRG inscription on spin-coated films, which increases with azo content, is highest for the purely ionic azoSO 3 /PDMQ complex despite its very high T g , while the proton transfer azoCOOH/ PDM complexes, involving ionic and H-bonding with acid-salt structures, show somewhat more efficient SRG inscription than do the purely hydrogen-bonded azoOH/PDM complexes, and this despite some azoCOOH crystallization at the highest molar ratios. These findings clarify the comparative effectiveness of different supramolecular bond types on SRG inscription and provide a useful guide for the design of supramolecular photoresponsive polymers for SRG applications.

Supramolecular design principles for efficient photoresponsive polymer–azobenzene complexes

“…13. 83 The T g of the starting polymer is low (20 1C) but increases with degree of complexation and is very high for the purely ionic complex (180 1C). As shown in Fig.…”

“…In various systems, successful complexation generates liquid crystallinity, often not present in the pure components and which is generally characterized by a combination of DSC, polarized optical microscopy (POM) and X-ray techniques (WAXD and small angle scattering, which can also be applied to thin films in grazing incidence angle configuration). [81][82][83] The combination of illumination with any of the characterization tools mentioned above can provide valuable insights into what happens to the supramolecular bond during photoisomerization, i.e. when there is photoinduced motion in the material.…”

Recent Developments in Polymeric Assemblies and Functional Materials by Halogen Bonding

“…During the past decades, significant progress has been made in designing self‐assembled azobenzene‐functionalized photoresponsive polymeric materials [29] . In this regard, different supramolecular strategies have been employed for noncovalently grafting azobenzene pendants to P4VP backbones for photoinduced surface pattering and macroscopic motions, mostly exploiting ionic, H‐ and X‐bonding interactions [30] . Such patterns are obtained via cis‐trans isomerization of the photoactive azobenzene pendants that translate the molecular motion to macroscopic mechanical movements in the polymer matrix.…”

Photo-triggered large mass transport driven only by a photoresponsive surface skin layer

“…In 1995, Natansohn’s 1 and Tripathy’s 2 groups independently reported the induction of surface relief gratings (SRGs) on Az amorphous films using interference irradiation of two laser beams. Since then, photoinduced SRG processes have been reported using various photofunctional materials such as amorphous polymers 1 – 20 , side chain liquid crystalline polymers (SCLCPs) 21 – 27 , supramolecular systems 24 , 27 – 29 , amorphous molecular materials 30 . Additionally, SRG formation can be realised using other photoresponsive units 31 – 35 .…”