The Impact of the Azo-Chromophore Sort on the Features of the Supramolecular Azopolyimide Films Desired to Be Used as Substrates for Flexible Electronics.

High-performance supramolecular polyimide systems were synthesized via a simple and innovative approach using two types of azo-chromophores, leading to concomitant special properties: high thermostability, the ability to be processed in the form of films with high flexibility, adequate morphological features, and good structuring capacity via phase mask ultraviolet (UV) laser irradiation, induced by the presence of the azo groups (-N=N-). The dimension and the anisotropy degree of the micro/nano patterns obtained on the surface of the flexible films (determined by atomic force microscopy) depend on the azo-dye type used in the supramolecular azopolyimide synthesis, which were higher when the azo-chromophore containing a -cyano group (-C≡N) was used. The molecular dynamics method, an excellent tool for an in-depth examination of the intermolecular interactions, was used to explain the morphological aspects. Energetic, dynamic and structural parameters were calculated for the two systems containing azo-chromophores, as well as for the pristine polymer system. It was highlighted that the van der Waals forces make a major contribution to the intermolecular interactions. The results from the combination of the dynamic analysis and the concentration profile explain the better mobility of the polyimide chains with a maximum content of azo groups in the cis configuration compared to the other systems. Taking all these data into account, the surfaces of the films can be tuned as required for the proposed applications, namely as substrates for flexible electronis.

Polynaphthylimide-Azomethines Containing Triphenylamine or Carbazole Moieties with Tuned Optoelectronic Properties through Molecular Design.

Polyazomethines containing electron-donor triphenylamine (TPA) or carbazole (Cbz) and electron-acceptor naphthyl(di)imide were synthesized and investigated with regard to thermal, optical and electronic features, with a focus on their modulation by molecular design. The polycondesation of an imido-based diamine with a Cbz- or TPA-based dialdehyde led to donor-acceptor polymers with good thermostability, up to 318 °C. These displayed good solubility in organic solvents, which enabled easy polymer processability in thin films with different molecular assemblies. The molecular order improved the charge carrier's mobility, with a direct impact on the bandgap energy. The optical properties studied by UV-Vis absorption and fluorescence experiments showed solvent-dependence, characteristic for donor-acceptor systems. The structural parameters exerted a strong influence on the light-emissive behavior, with the prevalence of intrinsic or intramolecular charge transfer fluorescence contingent on the donor-acceptor strength and polymer geometry. All polymers showed good electroactivity, supporting both electrons and holes transport. The exchange of Cbz with TPA proved to be an efficient tool with which to decrease the bandgap energy, while that of naphthyl(di)imide with bis(naphthylimide) was beneficial for fluorescence enhancement. This study may contribute to a deeper understanding of the physico-chemistry of electronic materials so as to make them more competitive in the newest energy-related or other optoelectronic devices.

Evaluation of Local Mechanical and Chemical Properties via AFM as a Tool for Understanding the Formation Mechanism of Pulsed UV Laser-Nanoinduced Patterns on Azo-Naphthalene-Based Polyimide Films.

Aromatic polyimides containing side azo-naphthalene groups have been investigated regarding their capacity of generating surface relief gratings (SRGs) under pulsed UV laser irradiation through phase masks, using different fluencies and pulse numbers. The process of the material photo-fluidization and the supramolecular re-organization of the surface were investigated using atomic force microscopy (AFM). At first, an AFM nanoscale topographical analysis of the induced SRGs was performed in terms of morphology and tridimensional amplitude, spatial, hybrid, and functional parameters. Afterward, a nanomechanical characterization of SRGs using an advanced method, namely, AFM PinPoint mode, was performed, where the quantitative nanomechanical properties (i.e., modulus, adhesion, deformation) of the nanostructured azo-polyimide surfaces were acquired with a highly correlated topographic registration. This method proved to be very effective in understanding the formation mechanism of the surface modulations during pulsed UV laser irradiation. Additionally to AFM investigations, confocal Raman measurements and molecular simulations were performed to provide information about structured azo-polyimide chemical composition and macromolecular conformation induced by laser irradiation.