PMMA Film Research Articles

Dinuclear PtII Complexes with Strong Blue Phosphorescence for Operationally Stable Organic Light‐Emitting Diodes with EQE up to 23 % at 1000 cd m−2

AbstractHere we describe the synthesis and characterization of a new class of dinuclear PtII complexes with blue phosphorescence. Bulky N‐heterocyclic carbene and tethered bridging ligands were employed to suppress photo‐induced structural changes and to improve thermal stability of the complexes. These complexes show mixed 3IL/3MLCT blue emission (≈460 nm) with emission quantum yields of up to 0.95, emission lifetimes of as low as 1.3 μs and radiative decay rate constants of up to 7.3×105 s−1 in 4 wt % doped PMMA films; the latter is attributed to a 1MLCT excited state having high metal character (resulting in a large SOC) and a large transition dipole moment, based on DFT calculations. Phosphor‐sensitized blue hyper‐OLEDs with Commission Internationale de L'Eclairage (CIE) coordinates of (0.13, 0.12) showed a maximum EQE of 23.4 % with a full‐width‐at‐half‐maximum of 18 nm and a LT50 >250 h at an L0 of 1000 cd m−2.

One-step 3D microstructuring of PMMA using MeV light ions

The conventional procedure for creating 3D microstructures in resists by ion beam lithography consists of two stages – exposure and developing. However, single stage of manufacturing 3D structures in resist is also possible. Irradiation of PMMA can cause it to shrink. This feature of the polymer can be used for one-step three-dimensional microstructuring, which simplifies the manufacturing process. The shrinkage of PMMA film on a substrate has been extensively studied, while research on free-standing film is not comprehensive. The use of free-standing PMMA film allows the creation of a flexible material with 3D microstructures, which can be used in medicine, optics, and electronics. The question here is whether the results obtained for the PMMA film on the substrate are applicable to the freestanding film. Since the nature of shrinking is outgassing of volatile products, the film on the substrate has only one surface for the release of gases, while in the free-standing film, gases can be released from the sample from both sides. Therefore, the shrinking in the free-standing film occurs on both sides. The aim of this work is to study the shrinkage of the free-standing film and compare it with that of the film of the same thickness coated on the substrate.

Enhancement of fluorescence and photostability of luminescent radicals by quadruple addition of phenyl groups

A photostable luminescent radical with four 4-methoxyphenyl groups showed bright fluorescence in nonpolar solvents. A photostable luminescent radical with four phenyl groups exhibited bright fluorescence also in polar solvents and PMMA film.

Room-temperature luminescence from Pd(II) and Pt(II) complexes: from mechanochromic crystals to flexible polymer matrices.

A series of Pd(II) (PdLOMe, PdLOHex) and Pt(II) (PtLOMe, PtLOHex) complexes bearing tetradentate ligands as dianionic luminophores were synthesized. Hence, the cyclometallating chelators were alternatively decorated with two n-hexyloxy (LOHex) or two methoxy (LOMe) moieties to promote crystallization and processability. The new compounds were unambiguously characterized by means of multiple NMR spectroscopies and mass spectrometry as well as by single crystal X-ray diffractometric analysis (PtLOMe and PdLOMe). Steady state and time-resolved photoluminescence spectroscopic studies were carried out in crystalline phases, in fluid solutions at room temperature, in frozen glassy matrices at 77 K and in a flexible polymeric matrix (PMMA). PtLOMe presents an intriguing mechanochromism resulting from the responsive metal-metal interactions involving adjacent monomeric units. Incorporation of the Pd(II) complexes into the polymeric matrix boosts their photophysical properties by stiffening of the coordination environment while reducing non-radiative deactivation pathways mediated by dissociative metal-centred states, which also become thermally inaccessible at 77 K.

Effectively polymer composition controllable optical properties of PVDF/PMMA blend films for advances in flexible device technologies

Polymer blends and their matrices-based nanocomposites have been established as potential candidates in the advancement of optoelectronic and microelectronic device technologies because they bear attractive design flexibility and also tunable optical and dielectric properties. In this research, we prepared the poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blend films with varying constituents concentration (viz. PVDF/PMMA=100/0, 80/20, 60/40, 40/60, 20/80, 0/100 wt/wt%), and these were investigated by employing ultraviolet-visible (UV-Vis) spectrophotometer for their in-detail optical characterization. The absorbance, reflectance, and transmittance spectra of these PVDF/PMMA blend films in the wavelength range from 200 nm to 800 nm were analyzed and considered to determine the values of various optical parameters. Due to significant differences in optical behaviour of the PVDF film and that of the PMMA film, the values of the direct energy band gap, extinction coefficient, refractive index, single oscillator energy, dispersive energy, optical range complex dielectric permittivity, optical conductivity, linear susceptibility, third-order non-linear susceptibility, and non-linear refractive index of the PVDF/PMMA blend films were found appreciably blend composition controllable. The energy bandgap, refractive index, and extinction coefficient of these materials are found in the ranges 5.42 to 4.93 eV, 2.22 to 1.72, and 6.62x10 4 to 0.64x10 4 , respectively. The experimental results offer a new paradigm for the use of these materials in the design and development of next-generation flexible optoelectronic and allied devices.

Highly Ordered Polymer Nanostructures via Solvent On-Film Annealing for Surface-Enhanced Raman Scattering.

Surface-enhanced Raman scattering (SERS) has been a useful sensing technique, in which inelastic light scattering can be significantly enhanced by absorbing molecules onto rough metal surfaces or nanoparticles. Although many methods have been developed to prepare SERS substrates, it is still highly desirable and challenging to design SERS substrates, especially with highly ordered and controlled three-dimensional (3D) structures. In this work, we develop novel SERS substrates with regular volcano-shaped polymer structures using the versatile solvent on-film annealing method. Polystyrene (PS) nanospheres are first synthesized by surfactant-free emulsion polymerization and assembled on poly(methyl methacrylate) (PMMA) films. After annealing in acetic acid vapors, PMMA chains are selectively swollen and wet the surfaces of the PS nanospheres. By selectively removing the PS nanospheres using cyclohexane, volcano-shaped PMMA films can be obtained. Compared with flat PMMA films with water contact angles of ∼74°, volcano-shaped PMMA films exhibit higher water contact angles of ∼110° due to the sharp features and rough surfaces. The volcano-shaped PMMA films are then coated with gold nanoparticles (AuNPs) as SERS substrates. Using rhodamine 6G as the probe molecules, the SERS results show that the Raman signals of the volcano-shaped PMMA/AuNP hybrid substrates are much higher than those of the pristine PMMA films and PMMA films with AuNPs. For the volcano-shaped PMMA/AuNP hybrid substrates using 400 nm PS nanospheres, a high enhancement factor (EF) value of ∼1.12 × 105 with a detection limit of 10-8 M is obtained in a short integration time of 1 s. A linear calibration line with an R2 value of 0.918 is also established, demonstrating the ability to determine the concentrations of the analytes. This work offers significant insight into developing novel SERS substrates, which is crucial for improving the detection limits of analytes.

Suspended Palladium/Polymer Bilayer for High-Contrast and Fast Hydrogen Sensors.

Hydrogen sensing is extremely essential for hydrogen-related applications due to the explosibility of hydrogen gas (H2). Here, we first present a high-contrast and fast optical hydrogen sensor, which is a partially suspended Pd/PMMA bilayer on a PDMS substrate with a microgroove array on the surface. The suspended structure reduces constraints from the substrate on the Pd film, leading to a large wrinkling amplitude and fast response rate during hydrogenation. The PMMA film can protect the Pd film from the poisonous impurities in the air and improve the flexibility of the bilayer. When exposed to 4% H2 mixed with air, the reflectance of the sensor drops down from 43 to 4% at 600 nm wavelength, in which the corresponding reflectance contrast, defined as the ratio of the reflectances before and after exposure to hydrogen, is 10.75. Such a high reflectance variation results from the light scattering induced by the wrinkling of the suspended Pd/PMMA bilayer during hydrogenation. Meanwhile, the sensor has a fast response that the reflectance can decrease from 43 to 33% within 0.6 s. Moreover, the sensor shows good recyclability and hydrogen selectivity. These excellent performances suggest that our suspended Pd/PMMA bilayer has great potential for practical hydrogen detection.

Tuning the Excited State of Tetradentate Pd(II) and Pt(II) Complexes through Benzannulated N‐Heteroaromatic Ring and Central Metal

Comprehensive SummaryA series of tetradentate Pd(II) and Pt(II) complexes containing fused 5/6/6 metallocycles with phenyl N‐heteroaromatic benzo[d]imidazole (pbiz), benzo[d]oxazole (pboz) or benzo[d]thiazole (pbthz)‐containing ligands was developed. Systematic studies by experiments and theoretical calculations reveal that both the central metal and the benzannulated N‐heteroaromatic ring have significant influence on the electrochemical, photophysical and excited‐state properties of the Pd(II) and Pt(II) complexes. In identical condition, compared to pbiz‐based Pd(II) and Pt(II) complexes, the corresponding metal complexes with pboz and pbthz‐containing ligand show significant red‐shift emission spectra. Pd(II) complexes exhibit blue‐shift emission spectra in comparison with the corresponding Pt(II) complexes. The Pt(II) complexes possess more metal‐to‐ligand charge transfer (3MLCT) character in their T1 states, which enables the Pt(II) complexes to have much higher quantum efficiencies (ΦPL) and shorter excited‐state lifetimes (τ), resulting in large radiative decay rates (kr). Especially, Pt(pbiz) has a ΦPL of 94% with a τ of 4.0 μs in 5 wt% doped PMMA film at room temperature. Pt(pbiz)‐doped green organic light‐emitting diode (OLED) using 26mCPy as host demonstrated a peak external quantum efficiency (EQE) of 21.6% and a maximum brightness (Lmax) of 55481 cd/m2, which still maintained an EQE of 16.5% and 10.8% at 1000 and 10000 cd/m2, respectively.

Improving the Energy Density and Efficiency of the Linear Polymer PMMA with a Double-Bond Fluoropolymer at Elevated Temperatures.

A variety of applications can be found for high-temperature film capacitors, including energy storage components and pulsed power sources. In this work, in order to increase the energy density (Ue), poly(vinylidene fluoride-chlorotrifluoroethylene-double bond) (P-DB) is introduced into poly(methyl methacrylate) (PMMA) to manufacture composite films by a solution casting process. In the case of the pure PMMA film, there is significant improvement in the polarization (Pmax) and breakdown field (Eb) of the composite film. These improvements can effectively increase the Ue of the composite film at room temperature and the elevated temperature. The results show that at an elevated temperature of 90 °C and at 350 MV/m, the Ue of 40 vol % P-DB reaches 8.7 J/cm3, and the efficiency (η) of 77% is also considerable. Compared with biaxially oriented polypropylene (2.0 J/cm3), the proposed film exhibits 4 times enhancement in the energy storage density, meaning that it can be an energy storage capacitor with huge potential at high temperatures.

Improving photoluminescence, optical and electrical characteristics of PMMA films with gamma irradiation

Polymeric materials are macromolecules, essentially a combination of numerous repeated subunits. Polymers are innovative and advanced materials that currently have a strong impact on our daily lives. In recent years, polymer use has been prominent due to the materials’ distinctive properties; thus, they entered different fields of science, technology and industrial-biomedical applications.The improvement of photoluminescence, optical and electrical characteristics of non-conducting Poly(methyl methacrylate) (PMMA) films was studied. Upon gamma irradiation of various doses, the photophysical and electrical properties of PMMA films were investigated using photoluminescence spectroscopy, ultraviolet–visible (UV–vis) spectroscopy and the LCR Meter Bridge Circuit technique. The fluorescent response improved the photoluminescence (PL) spectral emission peaks according to gamma values. Strong fluorescence peaks appeared with the highest gamma dose. The UV–Vis results revealed a significant red-shift in the absorption edge as gamma doses increased. This shift exhibits a continuous decrease in the energy band gap values (from 3.50 to 2.60 eV for direct transition and from 3.05 to 1.55 eV for indirect transition). This was due to the formation of carbon clusters, which led to an increase in the electrical conductivity and improved the dielectric parameters of the irradiated PMMA films. Among a variety of measurements presented and discussed in the present study, the electrical measurements showed improved electrical characteristics of gamma-irradiated PMMA films.

Preparation and Optical Characterization of PMMA Thin Films of C1

AbstractIn this study, thin films of PMMA (poly methylmethacrylate) and chalcones are prepared via drop casting method. A newly synthesized Chalcone derivative namely 1‐(3‐Methoxy‐phenyl)‐3‐(4‐napthalen‐yl)‐propenone (C1) are used for doping films with different concentrations. Films prepared are transparent and so they are considered for analysis in photonic applications. Different spectroscopic techniques are used for optical characterization of the samples. From the absorption spectra, optical parameters are determined like band gap energies, refractive index, and extinction coefficient. The way these parameters are affected by doping concentration is studied and plotted graphically. The doping effect is also analyzed on emission spectra. Also, FTIR spectra for doped films is determined and compared with that of the pure compound to notice alterations in the peak values so as to note the change in intensities.

Precise localization of DBD plasma streamers using topographically patterned insulators for maskless structural and chemical modification of surfaces

Dielectric insulators with patterned topographic relief were used in dielectric barrier discharge (DBD) plasmas operating at atmospheric pressure to spatially define the formation of filamentary microdischarges (“plasma streamers”). Precise localization of microdischarge streamers is demonstrated with concomitant treatment patterns on surfaces, enabling localized etching, surface micro-texturing, and chemically and structurally induced wettability modification without the use of lithographic masks on the sample. Proof-of-concept examples include generation of arbitrary streamer patterns (lines, arrays, and letters), anisotropic etching of PMMA films, and spatial patterning of Teflon to be hydrophilic. The approach herein allows user-defined patterning of DBD streamers for subsequent modification and treatment of surfaces (e.g., roughness, wettability, etc.), materials deposition, or etching.

Luminescence behavior of PMMA films doped with Tb(III) and Eu(III) complexes

Novel hybrid systems based on the poly(methyl methacrylate) (PMMA) matrix and Eu(III) and Tb(III) tris(β-diketonates) complexes with 1,10-phenanthroline were synthesized and analyzed as light-conversion materials. Solutions of the Tb(III) and Eu(III) complexes doped into PMMA were spin-coated to fabricate films with various concentrations of luminophores. Long hydrocarbon substituents in the structure of complexes inhibit their crystallization. In turn, it allows to vary the luminophore content in a polymer matrix in a broader range and achieve the maximum of emission with higher concentrations of dopants. The addition of the Tb(III) complex to the system results in a 26% increase in the relative luminescence quantum yield of the Eu(III) ions due to an additional energy transfer from the Tb(III) compound. The results of this work illustrate that although the Eu(III) and Tb(III) complexes exhibit lower rate and efficiency of energy transfer than their well-known Tb(acac)3 and Eu(tta)3 analogues, the structural features of lanthanide complexes allow to efficiently dope a PMMA matrix with considerably larger amounts of luminophores. It offers broader application opportunities for the coordination Ln(III) compounds as polyfunctional materials for optics and optoelectronics.

Linear Carbene Pyridine Copper Complexes with Sterically Demanding N,N'-Bis(trityl)imidazolylidene: Syntheses, Molecular Structures, and Photophysical Properties.

The sterically demanding carbene ITr (N,N'-bis(triphenylmethyl)imidazolylidene) was used as a ligand for the preparation of luminescent copper(I) complexes of the type [(ITr)Cu(R-pyridine/R'-quinoline)]BF4 (R = H, 4-CN, 4-CHO, 2,6-NH2, and R' = 8-Cl, 6-Me). The selective formation of linear, bis(coordinated) complexes was observed for a series of pyridine and quinoline derivatives. Only in the case of 4-cyanopyridine a one-dimensional coordination polymer was formed, in which the cyano group of the cyanopyridine ligand additionally binds to another Cu atom in a bridging manner, thus leading to a trigonal planar coordination environment. In contrast, employing sterically less demanding monotrityl-substituted carbene 3, no (NHC)Cu-pyridine complexes could be prepared. Instead, a bis-carbene complex [(3)2Cu]PF6 was obtained which showed no luminescence. All linear pyridine/quinoline coordinated complexes show weak emission in solution but intense blue to orange luminescence doped with 10% in PMMA films and in the solid state either from triplet excited states with unusually long lifetimes of up to 4.8 ms or via TADF with high radiative rate constants of up to 1.7 × 105 s-1 at room temperature. Combined density functional theory and multireference configuration interaction calculations have been performed to rationalize the involved photophysics of these complexes. They reveal a high density of low-lying electronic states with mixed MLCT, LLCT, and LC character where the electronic structures of the absorbing and emitting state are not necessarily identical.

Thermal and optical properties of PMMA films reinforced with Nb2O5 nanoparticles

The article presents the thermal and physical properties of PMMA composite films with the addition of Nb2O5 nanoparticles. The addition of nanoparticles to PMMA mainly influenced the optical transmission and glass transition temperature of composite films compared to pure PMMA. It is clearly visible in the results of the conducted ellipsometric and differential scanning calorimetry tests. X-ray studies showed that the heat treatment of the samples resulted in the ordering of the polymer structure (flattening of the polymer chains). Examining the surface of the samples with scanning electron microscopy, it can be seen that Nb2O5 nanoparticles formed unusual, branched formations resembling "snowflakes".

Encapsulation-Enabled Perovskite-PMMA Films Combining a Micro-LED for High-Speed White-Light Communication.

Cesium lead halide perovskite nanocrystals have recently become emerging materials for color conversion in visible light communication (VLC) and solid-state lighting (SSL), due to their fast response and desirable optical properties. Herein, perovskite nanocrystal-polymethyl methacrylate (PNC-PMMA) films with red and yellow emission are prepared. The PNC-PMMA films, with optical properties such as a short lifetime and air stability, are used to make broadband color converters based on a high-bandwidth 75 μm blue micro-LED (μLED) for VLC. The yellow-emitting CsPb(Br/I)3 PNC-PMMA has a high bandwidth of 347 MHz, while the red-emitting CsPbI3 PNC-PMMA exhibits a higher modulation bandwidth of 822 MHz, which is ∼65 times larger than that of conventional phosphors. After fixing the two PNC-PMMA films in front of the μLED, a qualified warm white light is generated with a correlated color temperature of 5670 K, a color rendering index of 75.7, and a de L'Eclairage (CIE) coordinate at (0.33, 0.35). Although the color conversion of the blue light sacrifices some received power and slightly reduces the overall bandwidth from 1.130 to 1.005 GHz, a maximum real-time data rate of 1.7 Gbps is still achievable using the non-return-to-zero on-off keying modulation scheme, which is ∼6 times higher than that of the previous record. This study provides a practical approach to develop a considerably high-bandwidth white-light system for both high-speed VLC and high-quality SSL.

Burger Model as the Best Option for Modeling of Viscoelastic Behavior of Resists for Nanoimprint Lithography.

In this study, Atomic Force Microscopy-based nanoindentation (AFM-NI) with diamond-like carbon (DLC) coated tip was used to analyze the mechanical response of poly(methyl methacrylate) (PMMA) thin films (thicknesses: 235 and 513 nm) on a silicon substrate. Then, Oliver and Pharr (OP) model was used to calculate hardness and Young’s modulus, while three different Static Linear Solid models were used to fit the creep curve and measure creep compliance, Young’s modulus, and viscosity. Values were compared with each other, and the best-suited method was suggested. The impact of four temperatures below the glass transition temperature and varied indentation depth on the mechanical properties has been analyzed. The results show high sensitivity on experiment parameters and there is a clear difference between thin and thick film. According to the requirements in the nanoimprint lithography (NIL), the ratio of hardness at demolding temperature to viscosity at molding temperature was introduced as a simple parameter for prediction of resist suitability for NIL. Finally, thinner PMMA film was tentatively attributed as more suitable for NIL.

Photophysical Properties of Cyclometalated Platinum(II) Diphosphine Compounds in the Solid State and in PMMA Films.

Platinum(II) compounds were synthesized with both chelate cyclometalated ligands and chelate diphosphine ligands. The cyclometalated ligands include phenylpyridine and a benzothiophene-containing ligand. The three new benzothiophene compounds were characterized by nuclear magnetic resonance (NMR) spectroscopy, high-resolution mass spectrometry (HR-MS), and photophysical measurements. In the case of one compound, L1-DPPM, the structure was determined by single crystal X-ray diffraction. The structural coherence of the noncrystalline emissive solid state was measured by X-ray total scattering real space pair distribution function analysis. Quantum yield values of all of the platinum compounds measured in the solid state and in PMMA films were much greater than in solution.

Ag-Doped ZnInS/ZnS Core/Shell Quantum Dots for Display Applications

Development of nontoxic quantum dots (QDs) exhibiting superior photoluminescence properties is a major challenge in the commercialization of QDs-based solid-state lighting or display device applications. This work reports the synthesis of heavy-metal-free Ag:Zn–In–S/ZnS (Ag:ZIS/ZS) core/shell QDs via the heating-up method followed by a nonaqueous hot-injection route. Formation of the QDs, their growth, and structural qualities were studied by high-resolution transmission electron microscopy and XRD analysis. The optical properties of these QDs were investigated through absorption, photoluminescence, and time-resolved fluorescence decay spectroscopic measurements. Surface passivation of the core Ag:ZIS QDs was done by coating ZnS layers on them. The successful doping of Ag+ into the ZnInS host material changed the emission characteristics; the influence of Ag loading and the shell thickness on the optical features were studied. The shell thickness had a strong impact on the photophysics of the nanocrystal with enhanced radiative lifetime. By regulating the Ag concentration, the Ag:ZIS core QDs showed a wide ranging tunable emission from 392 to 547 nm with a prominent blue shift with the introduction of ZnS shell layers. The blue shift in the band gap energy and emission wavelength has been reported to be due to the cation-exchange process of Ag:ZIS/ZS core/shell QDs. The radiative excited state lifetime is prolonged with subsequent injection of shells with the highest reported value being 504.72 ns. These nontoxic core/shell QDs, endowed with notable spectral emission within the visible spectrum, can be used as a down-converting material by tailoring the dopant concentration and shell precursor injection. Furthermore, a nanocomposite film of PMMA–QDs was synthesized by the drop-casting method, and its overall luminous efficacy complements that of parental core/shell QDs without quenching. The transmittance plot delineates that the optical transparency of the film can be engineered over the entire visible spectrum by varying the dopant (Ag) concentration.

Yellow–green luminescence of four-coordinate copper(I) complexes bearing N–heterocyclic carbene (NHC) ligands: Synthesis, photophysical and computational studies

The synthesis and photophysical investigation of a series of six copper(I) complexes bearing benzimidazolylidene–type N–heterocyclic carbene (NHC) ligands with different groups are reported. Their photophysical properties can be tuned by adjusting the groups at the R1/R2 positions of the pyridine ring. The lowest-lying metal–to–ligand (MLCT) absorption bands at 325–437 nm can be observed for all the complexes. Upon excitation with UV light all the complexes emit bright yellow-green light (λem = 540–573 nm) with higher emission quantum yields of 21.1–55.6% and excited state lifetimes on the microsecond scale (τ = 30.6–62.1 μs) in PMMA films. The substituents (R2 = COCH3, F, Br, CH3, or OCH3) on R2–position of the pyridine ring were shown to have effects on the emission wavelengths of these complexes, while the introduction of R1 substituents (R1 = CH3) shows negligible effects on the emission wavelength but allow the enhancement of photoluminescence quantum yield (Φ) of the complexes. Additionally, the electronic properties, absorption and emission profiles of these complexes were further explored using DFT/TDDFT methods.