Spontaneous Formation of Complex Periodic Superstructures under High Interferential Illumination of Small‐Molecule‐Based Photochromic Materials

Abstract

A series of push‐pull azo compounds containing bulky substituents are synthesized, yielding fully amorphous materials with glass‐transition temperatures above 200 °C. Thin films are subjected to holographic illumination and show superior bulk photomigration in terms of speed and efficiency compared to materials exhibiting similar electronic and photochromic properties in the solid state. The reported results give evidence that a microscopic consideration of the free volume rather than macroscopic parameters like the glass‐transition temperature should to be adopted to interpret the matrix stiffness and its deformation ability. Irradiation performed at higher laser intensity produces periodic superstructures whose height is five to six times as high as the initial film thickness. The surface tension and instability effects are put forward to interpret the growth of such superstructures.

Synthesis and photoinduced surface relief grating formation of novel photo-responsive amorphous molecular materials, 4-[bis(9,9-dimethylfluoren-2-yl)amino]-4′-cyanoazobenzene and 4-[bis(9,9-dimethylfluoren-2-yl)-amino]-4′-nitroazobenzene

“…In addition, the increase of glass-transition temperature (Tg) of the material was found to be favorable for photoinduced SRG formation [27]. Photoinduced SRG formation using amorphous molecular materials has also been reported by other groups [31][32][33][34][35]. However, the phenomena using photo-responsive amorphous molecular materials remain to be fully elucidated and therefore it is of importance to elucidate SRG-forming properties of a variety of azobenzenebased photo-responsive amorphous molecular materials in relation to their molecular structures, Tgs, reactivity, and other properties.…”

Azopolymer‐based micro‐ and nanopatterning for photonic applications

“…If the intensity profile is flat, but the amplitude of the electric‐field component in question is modulated, the material as a rule piles up in the areas where this amplitude is small. In some cases, however, no intensity or polarization gradient is required; spontaneous surface patterns have been formed even upon irradiating the sample with a collimated laser beam …”

“…Quite recently, it has been realized that patterned azopolymer films can be used as molds and etching masks for fast and cost‐effective microstructuring and nanostructuring of other materials. This has significantly broadened the application potential of azopolymer SRGs, since they can now be used as a starting point for creation of periodic (or self‐assembled quasiperiodic) structures out of essentially any material or combination of materials, and in a variety of shapes. In addition to the already discussed azopolymer‐based diffraction gratings that can indeed be used to control light emission, absorption, and transmission, one can also create such photonic elements as microlens arrays for optical signal processing and wavefront sensing, molecular alignment layers for liquid‐crystal displays, and various nondiffractive subwavelength gratings that can be used, for example, as ultrathin broadband polarizers and phase retarders, moth‐eye‐type broadband AR coatings, and plasmonic microstructures and nanostructures for near‐field optical applications including surface‐enhanced Raman scattering (SERS) and optics of metamaterials .…”

Strong Color Tuning of Self‐Assembled Azo‐Derived Phosphonic Acids upon Hydrogen Bonding

“…However, thermal analyses revealed a glass transition temperature T g at 218 °C (Figure S4). This value is 100 °C higher than those typically obtained with similar bulky azo compounds devoid of HBP units, and lets us suggest strong H‐bonding intermolecular interactions …”

“…This value is 100 8Ch igher than those typicallyo btainedw ith similar bulky azo compounds devoid of HBP units, and lets us suggest strong H-bonding intermolecular interactions. [23] ]…”