Electrochemical and Spectroelectrochemical Comparative Study of Macrocyclic Thermally Activated Delayed Fluorescent Compounds: Molecular Charge Stability vs OLED EQE Roll-Off

In this work, we present how a small change in molecular structure can affect the electrochemical stability of organic compounds. A new electron donor-acceptor-donor-acceptor (D-A-D-A) macrocyclic π-conjugated compound (tBuMC) comprising of dibenzophenazine as As and N,N’-bis(t-butylphenyl)-p-phenylenediamines as Ds has been synthesized. The photophysical investigation uncovered that tBuMC showed thermally activated delayed fluorescence and that the organic light-emitting diodes (OLEDs) fabricated with tBuMC as the emitter achieved high external quantum efficiency (EQEs) of ca. 10%. However, the OLED with tBuMC showed a slightly lower EQE than that of the OLED with MC (11.6%) and showed greater EQE roll-off. Comparative studies on electrochemical properties of tBuMC, MC, and a linear analogue (Linear) revealed the introduction of t-Bu groups in the D-A-D-A scaffold causes a significant change in redox behavior. Full electrochemical and spectroelectrochemical studies gave clues to understand how the steric hindering group is affecting the charge distribution in the new molecules which results in a significant difference in the OLED roll-off. The electrochemical investigations together with UV-Vis-NIR and EPR analyses supported by quantum chemical theoretical calculations were performed, which provided us insights on the effect of structural modification on the redox properties of the D-A-D-A scaffold.This is the peer reviewed version of the following article: A. Nyga, S. Izumi, H. F. Higginbotham, P. Stachelek, S. Pluczyk, P. de Silva, S. Minakata, Y. Takeda, P. Data, Asian J. Org. Chem. 2020, 9, 2153., which has been published in final form at https://doi.org/10.1002/ajoc.202000475. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving

Wide-range Angle-sensitive Plasmonic Color Printing on Lossy-Resonator Substrates

We demonstrate a sustainable, lithography-free process for generating non fading plasmonic colors with a prototype device that produces a wide range of vivid colors in red, green, and blue (RGB) ([0-1], [0-1], [0-1]) color space from violet (0.7, 0.72, 1) to blue (0.31, 0.80, 1) and from green (0.84, 1, 0.58) to orange (1, 0.58, 0.46). The proposed color-printing device architecture integrates a semi-transparent random metal film (RMF) with a metal back mirror to create a lossy asymmetric Fabry-P\'erot resonator. This device geometry allows for advanced control of the observed color through the five-degree multiplexing (RGB color space, angle, and polarization sensitivity). An extended color palette is then obtained through photomodification process and localized heating of the RMF layer under various femtosecond laser illumination conditions at the wavelengths of 400 nm and 800 nm. Colorful design samples with total areas up to 10 mm2 and 100 {\mu}m resolution are printed on 300-nm-thick films to demonstrate macroscopic high-resolution color generation. The proposed printing approach can be extended to other applications including laser marking, anti-counterfeiting and chromo-encryption

Absorption Enhancement in Peridinin–Chlorophyll–Protein Light-Harvesting Complexes Coupled to Semicontinuous Silver Film

We report on experimental and theoretical studies of plasmon-induced effects in a hybrid nanostructure composed of light-harvesting complexes and metallic nanoparticles in the form of semicontinuous silver film. The results of continuous-wave and time-resolved spectroscopy indicate that absorption of the light-harvesting complexes is strongly enhanced upon coupling with the metallic film spaced by 25 nm of a dielectric silica layer. This conclusion is corroborated by modeling, which confirms the morphology of the silver island film

Plasmonic nanomaterials for midinfrared and their photomodification

Semicontinuous metal films (SMFs) have been studied for several decades due to their unique optical properties. These films support the collective oscillations of conduction electrons, surface plasmons (SP) that can be excited by light in a metal structure. The SP resonance frequencies depend on the type of metal, the nanostructure geometry, and the surrounding medium. Plasmonic nanostructures act like optical nanoantennas. They can accumulate and build up electromagnetic energy in nanometer-scale areas called hot spots . This energy buildup results in high local fields and thus can produce a dramatic enhancement of optical responses. Materials supporting SP resonances can be used for applications such as surface-enhanced Raman spectroscopy with sensitivity high enough to enable single molecule detection, surface-enhanced infrared absorption, data recording, harmonic generation, absorption elements in solar cells and others. In this work we have studied the optical properties of plasmonic nanostructures in the visible and mid-IR range. The samples studied include e-beam evaporated SMFs and chemically synthesized core-shell metal-dielectric structures. Both sample types have fractal nanostructures with broad absorption bands extending from the UV to the midinfrared range. Laser photomodification processes on these metal-dielectric structures were studied. The induced changes in extinction of both types of studied structures are wavelength- and polarization-selective. Mid-IR long-pass filters have been fabricated using SMFs and their subsequent photomodification with picosecond and nanosecond pulsed lasers operating in the mid-IR. Additional experiments on the photomodification of gold nanostructures grown on silica microspheres have been performed and show promising results, similar to those obtained with planar structures

Surface Modification of ZnO Nanotubes by Ag and Au Coatings of Variable Thickness : Systematic Analysis of the Factors Leading to UV Light Emission Enhancement

Surface modification by plasmonic metals is one of the most promising ways to increase the band-to-band excitonic recombination in zinc oxide (ZnO) nanostructures. However, the metal-induced modulation of the UV light emission depends strongly on the production method, making it difficult to recognize the mechanism responsible for charge/energy transfer between the semiconductor and a metal. Therefore, in this study, the ZnO/Ag and Au hybrids were produced by the same, fully controlled experimental approach. ZnO nanotubes (NTs), fabricated by a template-assisted ALD synthesis, were coated by metals of variable mass thickness (1–6.5 nm thick) using the electron beam PVD technique. The deposited Ag and Au metals grew in the form of island films made of metallic nanoparticles (NPs). The size of the NPs and their size distribution decreased, while the spacing between the NPs increased as the mass of the deposited Ag and Au metals decreased. Systematic optical analysis allowed us to unravel a specific role of surface defects in ZnO NTs in the processes occurring at the ZnO/metal interface. The enhancement of the UV emission was observed only in the ZnO/Ag system. The phenomena were tentatively ascribed to the coupling between the defect-related (DL) excitonic recombination in ZnO and the localized surface plasmon resonance (LSPR) at the Ag NPs. However, the enhancement of UV light was observed only for a narrow range of Ag NP dimensions, indicating the great importance of the size and internanoparticle spacing in the plasmonic coupling. Moreover, the enhancement factors were much stronger in ZnO NTs characterized by robust DL-related emission before metal deposition. In contrast to Ag, Au coatings caused quenching of the UV emission from ZnO NTs, which was attributed to the uncoupling between the DL and LSP energies in this system and a possible formation of the ohmic contact between the Au metal and the ZnO.Peer reviewe

Revisiting semicontinuous silver films as surface-enhanced Raman spectroscopy substrates

Surface-enhanced Raman spectroscopy (SERS) is a very promising analytical technique for the detection and identification of trace amounts of analytes. Among the many substrates used in SERS of great interest are nanostructures fabricated using physical methods, such as semicontinuous metal films obtained via electron beam physical vapor deposition. In these studies, we investigate the influence of morphology of semicontinuous silver films on their SERS properties. The morphologies studied ranged from isolated particles through percolated films to almost continuous films. We found that films below the percolation threshold (transition from dielectric-like to metal-like) made of isolated silver structures provided the largest SERS enhancement of 4-aminothiophenol (4-ATP) analyte signals. The substrate closest to the percolation threshold has the SERS signal about four times lower than the highest signal sample

Application of Turkevich Method for Gold Nanoparticles Synthesis to Fabrication of SiO2@Au and TiO2@Au Core-Shell Nanostructures

The Turkevich synthesis method of Au nanoparticles (AuNPs) was adopted for direct fabrication of SiO2@Au and TiO2@Au core-shell nanostructures. In this method, chloroauric acid was reduced with trisodium citrate in the presence of amine-functionalized silica or titania submicroparticles. Core-shells obtained in this way were compared to structures fabricated by mixing of Turkevich AuNPs with amine-functionalized silica or titania submicroparticles. It was found that by modification of reaction conditions of the first method, such as temperature and concentration of reagents, control over gold coverage on silicon dioxide particles has been achieved. Described method under certain conditions allows fabrication of semicontinuous gold films on the surface of silicon dioxide particles. To the best of our knowledge, this is the first report describing use of Turkevich method to direct fabrication of TiO2@Au core-shell nanostructures