Nowe azopoliamidoimidy i azopoliestroimidy : badania wpływu budowy chemicznej na właściwości fizyczne, w tym fotoindukowaną dwójłomność optyczną

The aim of the work was synthesis of novel, processable azopolymers and study of their selected physicochemical properties as well as the properties induced by the polarized light. The research was devoted to photochromic polyimides containing the amide or ester groups and derivatives of azobenzene or azopyridine. The azo-dyes were covalently bonded to the polymer main chain or formed “guest-host” polymers. The selected azopolyimides were applied as layers for the liquid crystal alignment within the cooperation with the Institute of Applied Physics of the Military Technical Academy in Warsaw. In a detailed study of physicochemical properties the attention was focused on determining the effect of such elements of polymer structure (including the possibility of formation of the hydrogen bonding) as (i) structure of the main chain, (ii) the type of azo-dye, as well as the type and place of azo-dye connection to the polymer macrochain, (iii) quantity of the azo groups in the repeating unit, on the amorphous structure, solubility, film forming properties, thermal and absorption properties in the UV-vis spectrum and the photoinduced birefringence. In this dissertation 21 low molecular compounds were prepared and used to synthesize 47 polymers, including 10 poly(amide imide)s and 7 poly(ester imide)s with covalently bonded derivatives of azobenzene, 5 poliimide matrices used to prepare 25 “guest-host” polyimides containing derivatives of azobenzene or azopyridine. It should be noted, that polyimides with derivatives of azopyridine have not been investigated in the context of generating the photoinduced birefringence yet. Moreover, systematic research on the influence of the chemical structure of azopolyimides on Δn has not been conducted. The innovative nature of this work is mainly related with the proposed modifications of the materials structure, which allowed to obtain polymers with a higher and more stable Δn value, with respect to the polyimides presented in the literature. In particular, the novelity of this work lies in applying the Fox’s formula to determine the glass transition temperature of “guest-host” polyimides. In addition, the DFT method was used for determining the possibility of formation of the hydrogen bonding in “guest-host” systems. The DFT results were confirmed by experimental methods (1H NMR and FTIR). The results obtained in the doctoral thesis allowed to formulate the relationships between the chemical structure of the investigated polymers and physicochemical properties including photoinduced birefringence values and its stability. In addition, the importance of the hydrogen bonds formation on the process of birefringence generation and relaxation was shown. The obtained results extend the general knowledge on azopolymers and may be also important from the point of view of potential applications, in particular as the layers for the liquid crystal alignment in optoelectronic devices: liquid crystal diffraction gratings, Fresnel’s lens and the structures that generate optical vortices

Azobenzene Functionalized “T-Type” Poly(Amide Imide)s vs. Guest-Host Systems - A Comparative Study of Structure-Property Relations

This paper describes the synthesis and characterization of new “T-type” azo poly(amide imide)s as well as guest-host systems based on the “T-type” matrices. The matrices possessed pyridine rings in a main-chain and azobenzene moieties located either between the amide or imide groups. The non-covalent polymers contained the molecularly dispersed 4-phenylazophenol or 4-[(4-methyl phenyl)diazinyl]phenol chromophores that are capable of forming intermolecular hydrogen bonds with the pyridine rings. The FTIR spectroscopy and the measurements of the thermal, optical and photoinduced optical birefringence were employed for the determination of the influence of H-bonds and the specific elements of polymer architecture on physicochemical properties. Moreover, the obtained results were compared to those described in our previous works to formulate structure-property relations that may be considered general for the class of “T-type” azo poly(amide imide)s

Photoinduced properties of "T-type" polyimides with azobenzene or azopyridine moieties

In this work series of “T-type” polyimides with azobenzene or azopyridine moieties were investigated. It is the first report where the “T-type” polyimides with derivatives of azopyridine were investigated. The cis-trans isomerization in the dark in the solid-state was showed. Polyimides with azobenzene derivatives exhibited higher stability of cis-trans recovery than their azobenzene analogues. For the inscription of the surface relief gratings, two different intensities of light (10 and 45 mJ/cm2) and a number of pulses (10 and 100) were used. Polyimides showed the modulation of SRGs up to almost 330 nm. Our studies showed, that azopolyimides are able to orient the nematic liquid crystal molecules in cell-based on effect at the twisted nematic. The obtained maximum value of tON was 0.9 ms (1 kHz, 1.5 V/μm) for polyimide with azobenzene moieties. Azopolyimides may be successfully used in many photonic devices based on the alignment of the liquid crystal mixture i.e. LC diffraction gratings, Fresnel lens, Vortex, in a photo-pattering technology for creating radical and azimuthal orienting layers

Photoresponsive behaviour of “T-type” azopolyimides. The unexpected high efficiency of diffraction gratings, modulations and stability of the SRG in azopoly(ether imide)

In this paper, we compare the light-induced properties of three “T-type“ polyimide containing azobenzene chromophores with the properties of their structural counterparts containing azopyridine moieties. The processes of photoinduced birefringence generation and surface relief grating (SRG) formation are efficient in azobenzene polyimides, while in the azopyridine analogues the processes are non-detectable. Density functional theory calculations performed to reveal a possible structural reason for the lack of optical response in the azopyridine materials showed a formation of intramolecular H-bonds. Azopoly(ether imide) with 2,2′-diphenylopropane structure despite relatively low chromophore content exhibited one of the highest diffraction efficiency (ca. 20%) and the largest modulation of the SRG (260 nm) as have ever been observed for azopolyimides. Two years after inscription, modulation of the SRG was still observed without a decrease in the relief depth, which is important in applications requiring long-term stability of SRGs

Surface Relief Modulated Grating in Azo Polymer—From the Tailoring of Diffraction Order to Reshaping of a Laser Beam

Among light-responsive materials for photonics, azo polymers occupy an important position due to their optical response and the related concepts of consecutive applications. However, scientific insight is still needed to understand the effects of irradiation on the modification of the azo polymer structure and the effect of this modification on incoming probing light. In this work, we report on a surface relief grating with a maximum depth of a record-high value of 1.7 µm, inscribed holographically in a custom synthesized glassy azo polymer belonging to the poly(ether imide) family. We show that the specifically deformed polymer, forming an amplitude-modulated relief grating, has a unique dual effect on an incoming light beam of different diameters. When illuminated by a narrow probe beam, the structure acts as a variable-depth grating, enabling a continuous tuning of the diffraction efficiencies in the entire theoretically predicted range and, thus, generating or eliminating diffracted waves of specified order. Alternatively, when illuminated by a wide probe beam, the whole structure acts as an optical component reshaping the Gaussian light intensity profile into the profiles resembling the squares of Bessel functions of the zeroth- or higher orders. Moreover, a physical justification of the effects observed is provided

Novel Azocoumarin Derivatives—Synthesis and Characterization

The paper presents synthesis and characterization of nine new thiazolyl-(phenyldiazenyl)-2H-chromen-2-one dyes. The impact of substituent structure in thiazole ring in the synthesized azocoumarin derivatives on electrochemical properties, photoisomerization process and photovoltaic response was examined. The dyes were electrochemically active and undergo reduction and oxidation processes. They showed low electrochemically estimated energy band gap in the range of 1.71–2.13 eV. Photoisomerization process of the synthesized molecules was studied in various solvents such as ethanol, chloroform and N,N-dimethylformamide (DMF) upon the UV illumination. It was found that novel azodyes showed reversible trans-cis-trans isomerization and exhibited long thermal back to the trans form, that was even 7 days in DMF. Selected azocoumarin were molecularly dispersed in polystyrene for preparation of guest-host azopolymer systems to study the cis-trans thermal isomerization of obtained dyes in solid state. The photovoltaic activity of the azochromophores was tested in bulk-heterojunction solar cells. They acting as weak donors in device with structure ITO/PEDOT:PSS/dye:PC70BM/Al. No photovoltaic response of cells with azocoumarin derivatives bearing 4-fluorobenzene, 3,4-dichlorobenzene, or 4-(1-adamantyl) unit was found. Additionally, dye which showed the best activity was examined in three-component solar cells ITO/PEDOT:PSS/PTB7:PC70BM:dye/PFN/Al