Enhanced photoinduced mass migration in supramolecular azopolymers by H-bond driven positional constraint

Laser & Photonics Reviews

et al. 2022

Self Cite

In optical devices like diffraction gratings and Fresnel lenses, light wavefront is engineered through the structuring of device surface morphology, within thicknesses comparable to the light wavelength. Fabrication of such diffractive optical elements involves highly accurate multistep lithographic processes that in fact set into stone both the surface morphology and optical functionality, resulting in intrinsically static devices. In this work, this fundamental limitation is overcome by introducing shapeshifting diffractive optical elements directly written on an erasable photoresponsive material, whose morphology can be changed in real time to provide different on-demand optical functionalities. First a lithographic configuration that allows writing/erasing cycles of aligned optical elements directly in the light path is developed. Then, the realization of complex diffractive gratings with arbitrary combinations of grating vectors is shown. Finally, a shapeshifting diffractive lens that is reconfigured in the light-path in order to change the imaging parameters of an optical system is demonstrated. The approach leapfrogs the state-of-the-art realization of optical Fourier surfaces by adding on-demand reconfiguration to the potential use in emerging areas in photonics, like transformation and planar optics.

Section: Resultsmentioning

confidence: 99%

Shapeshifting Diffractive Optical Devices

Oscurato

Reda

Laser & Photonics Reviews

et al. 2022

Self Cite

“…We also investigated by SCXRD the interaction in the supramolecular synthon of thioglycolic peripheral groups with the aminopyrimidine moiety of the azomolecule, after successful cocrystallization of compound t with 2-amino-4,6dimethoxypyrimidine (adp) in hot water, which afforded single crystals of the t(adp) 2 complex (Figure 2a). In the structure of the complex, each molecule of t is coordinated to two adp molecules through an AP-type supramolecular heterosynthon, while the third carboxyl is involved in an acid/acid type (AA) homosynthon (Figure 2a S2) 33 while a more ionic character of the interaction was observed in the case of Figure 2a Due to the stronger acidity of thioglycolic-type carboxylic group (pK a of thioglycolic acid = 3.55 38,39 ) compared to acetic acid (pK a = 4.76), easy conversion of dendrimer peripheral groups to Zn(II)-carboxylate can be directly accomplished in situ, during the formulation of the azomaterial in solution, by acid−base reaction with zinc acetate dihydrate. This mechanism, which may lead to an increase of the dendrimer generation, was demonstrated by preparing the zinc salt of the model compound mc (Figure 2b).…”

Section: Chemistry Of Materialsmentioning

confidence: 99%

Efficient High-Refractive-Index Azobenzene Dendrimers Based on a Hierarchical Supramolecular Approach

Fusco

Oscurato²,

et al. 2023

Chem. Mater.

Self Cite

Real-time manipulation of light in a diffractive optical element made with an azomaterial, through the lightinduced reconfiguration of its surface based on mass transport, is an ambitious goal that may enable new applications and technologies. The speed and the control over photopatterning/ reconfiguration of such devices are critically dependent on the photoresponsiveness of the material to the structuring light pattern and on the required extent of mass transport. In this regard, the higher the refractive index (RI) of the optical medium, the lower the total thickness and inscription time can be. In this work, we explore a flexible design of photopatternable azomaterials based on hierarchically ordered supramolecular interactions, used to construct dendrimer-like structures by mixing specially designed sulfur-rich, high-refractive-index photoactive and photopassive components in solution. We demonstrate that thioglycolic-type carboxylic acid groups can be selectively used as part of a supramolecular synthon based on hydrogen bonding or readily converted to carboxylate and participate in a Zn(II)−carboxylate interaction to modify the structure of the material and fine-tune the quality and efficiency of photoinduced mass transport. Compared with a conventional azopolymer, we demonstrate that it is possible to fabricate high-quality, thinner flat diffractive optical elements to reach the desired diffraction efficiency by increasing the RI of the material, achieved by maximizing the content of high molar refraction groups in the chemical structure of the monomers.

“…This peculiar photo-response is the result of a reversible material displacement, initiated, at microscopic level, by a multitude of actuations of the photo-active azobenzene molecules, which are repeatedly and cyclically switched between trans and cis isomeric forms by the absorption of UV/visible light 18 . The polarization-dependent probability of light absorption and the coordinated complex interaction of the azounits with the hosting polymeric environment generate an anisotropic polymer mass migration in the polarization direction, resulting in an efficient nanoscopic to macroscopic motion conversion, in which the azomolecules act as light-fueled molecular motors [18][19][20] . At the free surface of an azopolymer film, the light-driven material accumulates in an intensity/polarization-dependent relief pattern.…”

Section: Introductionmentioning

confidence: 99%

Reprogrammable diffractive micro-optical elements

Reda

Advanced Fabrication Technologies for Micro/Nano Optics and Photonics XVI

Borbone

et al. 2023

Self Cite

The fabrication of Diffractive Optical Elements (DOEs) involves the structuration of material surfaces with geometries on the scale of light wavelength. Differently to standard photoresists, thin films of amorphous azobenzene-containing polymers (azopolymers) directly develop surface reliefs in the irradiated area, directly usable as phase-modulating masks, acting as DOEs. Surface structuration is the result of an intrinsically reversible light-induced material displacement, which makes azopolymer films usable as photo-transformable planar diffractive optical devices. Here we demonstrate reprogrammable and ready-to-use diffractive gratings, lenses, and holographic projectors, directly obtained in a single photo-structuration step through the projection of a grayscale holographic pattern over the azopolymer film free surface. The all-optical scheme, based on the principles of computer-generated holography, allows a simple and accurate engineering of the light pattern used for the azopolymer surface structuration. Additionally, direct pattern transferring opens to the real-time optimization of the device allowing to test and prototype its diffraction properties right during the developing of structured surfaces. The proposed approach offers a versatile, efficient, and full-optical reversible fabrication framework for DOEs, making it a promising option to overcome the demanding, burdensome, and irreversible manufacturing processes typically involved in the realization of planar diffractive optical devices.