Organic LEDs Based on Bis(8-hydroxyquinoline) Zinc Derivatives with a Styryl Group.

For the first time, organic light-emitting diodes (OLEDs) based on bis(8-hydroxyquinoline) zinc with a styryl group (ZnStq) dispersed in poly(N-vinylcarbazole) matrix (ZnStq_R:PVK, where R = H, Cl, OCH3) were fabricated. The ZnStq_R:PVK films made via the spin-coating method were used as the active layer in these devices. The produced OLEDs showed strong electroluminescence with yellow emissions at 590, 587 and 578 nm for the ZnStq_H:PVK, ZnStq_Cl:PVK and ZnStq_OCH3:PVK, respectively. For all the studied thin films, the main photoluminescence emission bands were observed between 565 and 571 nm. The OLED with the ZnStq_OCH3:PVK layer with a narrow electroluminescence spectrum was found to have sufficient color purity to produce ultra-high-resolution displays with reduced power consumption (full width at half maximum of 59 nm, maximum brightness of 2244 cd/m2 and maximum current efficiency of 1.24 cd/A, with a turn-on voltage of 6.94 V and a threshold voltage of 7.35 V). To characterize the photophysical properties of the active layer, the ZnStq_R:PVK layers samples were additionally deposited on glass and silicon substrates. We found that the obtained results predestine ZnStq_R:PVK layers for use in the lighting industry in the future.

Effect of 2-Methylthiazole Group on Photoinduced Birefringence of Thiazole-Azo Dye Host-Guest Systems at Different Wavelengths of Irradiation.

The photoinduced birefringence behaviors of host-guest systems based on heterocyclic thiazole-azo dyes with different substituents, dispersed into PMMA matrix, were investigated under three excitation wavelengths, i.e., 405 nm, 445 nm or 532 nm. The wavelengths fell on the blue side, near the maximum or on the red side of the absorption bands of trans-azo dyes, respectively. We found that photoinduced birefringence was generated at a similar extent in all studied systems, except the system containing a 2-methyl-5-benzothiazolyl as thiazole-azo dye substituent. For this material, the achieved birefringence value was the highest among the whole series, regardless of the excitation wavelength. Moreover, we identified the optimal irradiation wavelength for efficient birefringence generation and showed that large absorption of excitation light by trans isomer does not account for achieving a significant degree of molecular alignment. The obtained results indicate that thiazole-azo dye with a 2-methyl-5-benzothiazolyl substituent shows promising photoinduced birefringence, and can be considered a dye potentially suitable for optical applications.

Spectroscopic Studies of Styrylquinoline Copolymers with Different Substituents.

The aim of the study was to present the influence of various styrylquinoline (StQ) substituents on the luminescence, structural, and optical properties of StQ-containing copolymers. StQ-containing copolymers were synthesized by free-radical thermoinitiated polymerization. The calculations of the copolymerization ratios for the obtained copolymers were based on the basis of the integrated peak areas of the 1H NMR spectra in CDCl3. The luminescence measurements show that the change in the nature of the electron-donating and electron-withdrawing of the substituent shifts the emission band to longer wavelengths and causes a transition from blue fluorescence to green or yellow and orange (or even white), regardless of the electronic nature of the introduced substituent group. The structural properties were measured by Fourier-Transform Infrared (FTIR) and Raman spectroscopies. For all of the compounds, we observed similarities in the bands in FTIR and Raman measurements. The optical parameters were obtained from the absorbance measurements. Additionally, Scanning Electron Microscopy (SEM) was used to study the surface topography of the thin layers on the glass substrate. The SEM images confirm that we obtained smoother layers for two copolymers. The computational Density Functional Theory (DFT) analysis fully supports the beneficial features of the analyzed systems for their applications in optoelectronic devices. Based on the obtained results, it can be concluded that all of the studied styrylquinolines are promising materials for applications in organic light-emitting diodes (OLEDs). However, COP1 with an OCH3 donor substituent possess a wider luminescence band, and its layer is smoother and more transparent.

Correlation between Nonlinear Optical Effects and Structural Features of Aurone-Based Methacrylic Polymeric Thin Films.

In this study, new photonics architectures and aurone-based methacrylic polymers were designed and synthesized for their optical and nonlinear optical properties. The studied polymeric thin films were deposited by spin coating method. SHG and THG effects were measured via Maker fringe technique in transmission mode and determined using theoretical models. Investigations involved the theoretical quantum chemical calculation of dipole moments, frontier molecular orbital HOMO and LUMO energies, and first (ß) and second (γ) hyperpolarizabilities. We determined the impact of the substitution in the para position of the phenyl ring and at the dipole moment of the chromophore on the nonlinear optical properties of the investigated polymers. The presented theoretical and experimental studies provide important information with respect to the design of methacrylic-based polymeric thin film devices and supplement existing knowledge with respect to their nonlinear behaviour.

Effect of UV-Irradiation and ZnO Nanoparticles on Nonlinear Optical Response of Specific Photochromic Polymers.

A series of methacrylic styrylquinoline polymers have been synthesized and characterized by spectroscopic and nonlinear optical (NLO) investigations. The NLO properties of studied polymer compounds in the form of thin films prepared by a spin coating method have been investigated by means of second and third harmonic generation via Maker fringe setup with a laser source at 1064 nm and a pulse duration of 30 ps. The results show strong second harmonic signal dependence on polarization configurations. This second harmonic generation (SHG) response was enhanced by UV-irradiation at 366 nm and doping by ZnO nanoparticles (NPs) (100 nm), while the opposite effect was achieved for a third harmonic generation experiment. Thus, values of second and third order nonlinear susceptibilities were determined by theoretical calculations based on comparative models. The remarkable NLO results presented in this paper expose potential optoelectronic and photonic applications.

Second- and third-order nonlinearities of novel push-pull azobenzene polymers.

In this work, the second- and third-order nonlinear optical response of spin-deposited thin films of three different push-pull side chain azobenzene polymers is investigated by the second- and third-harmonic Maker fringes techniques using 30 ps laser pulses at a fundamental wavelength of 1064 nm. Measurements were carried out before and after aligning the chromophores by corona poling of the films, while different polarization configurations have been utilized. Strong dependence of the response upon the structure of the systems has been found, which is related to the different charge transfer within the molecules. The reported findings are compared with already published results.