Excited-state optical properties of gold(I) organometallics are discussed with relevance to triplet-state light emission and nonlinear optical properties.

Synergetic enhancement of luminescence and ferroelectric (SELF) properties was achieved from the materials comprising a central luminophore (L) core with side chain groups, where side chain groups consist of a self-assembling group (SAG). LS molecules self-assembled through the intermolecular interaction of SAGs, inducing aggregation of luminophores. This was evidenced by the quenching of emission at SAGs (Eclip) accompanied by aggregation-induced emission enhancement of L units (EAIE). These LS molecules showed strong photoluminescence in a dilute solution and a significant EAIE in aqueous organic solution. LS film demonstrated SELF properties with high quantum yield of photoluminescence and ferroelectric switching. TPC4 was employed in light emitting electrochemical cells to achieve high luminance under pulsed current conditions. LS films exhibited high remnant polarization and piezoelectric constants at room temperature. Consequently, the SELF properties were employed in a piezoelectric nanogenerator, producing piezoelectric output under repeated bending. These results indicate that side chain interactions resulted in unprecedented flexible SELF properties in a single compound.

The photoactivation of Ru(II) complexes have been used in a number of applications, including solar energy conversion, sensors, and photoinduced drug delivery. The triplet metal-to-ligand charge transfer (3MLCT) excited state in these complexes is typically deactivated through a thermally accessible triplet metal-centered, ligand-field state (3LF). While a high-energy 3LF state is necessary to achieve a long-lived, emissive 3MLCT state for apllications that require energy/charge transfer, a low-lying 3LF state is desirable for the efficient drug delivery. Therefore, understanding the structural and electronic molecular features that affect the relative energies of these states is critical for optimizing the desired excited state properties for a given purpose. Properties desirable for optimizing the performance of these complexes will be discussed, along with examples of complexes that are able to both release a drug molecule upon irradiation and produce singlet oxygen to achieve cell death. These dual activity complexes are significantly more active than those that can either photorelease drugs or generate singlet oxygen.

We have prepared a series of four-coordinate metalloporphyrins (M(TPP), TPP is tetraphenylporphyrin and M(TPFPP), TPFPP is tetrapentafluorophenylpor-phyrin; M is Zn2+, Ni2+, Pt2+, or Pd2+) with distinct meso-substituents and their Magne-to-Optical Activity (MOA) was characterized by magnetic circular dichroism (MCD) and Magneto-Optical Rotary Dispersion spectroscopy (MORD; also known as Faraday Rotation spectroscopy). MORD spectra were calculated from the Kramers-Kronig relationship between MCD and MORD with the Hilbert transformation. The data show that the presence of the pentafluorophenyl group results in a significant increase in MOA in comparison to the phenyl group. The Gouterman four-orbital model is used to explain the MOA of these compounds.

Azo-functionalized copolymer holograms were fabricated for efficient generation of structured light beams. Holograms of size 2mm x 2mm were recorded/printed on polymer samples of size 3cm x 3cm and thickness 35 µm. When irradiated with a laser beam, the hologram emits several arbitrary structured light beams. A structured beam array consisting of 100 optical vortices was practically generated. Experimental generation of vector beams and Poincare beams are also reported. Diffraction efficiencies up to 85%, retention time up to 90-days, and a small size footprint of 2mm x 2mm makes it a promising candidate for optical information processing applications.

Applications of optical resins are expanding beyond conventional silica-based planar lightwave circuits to optical engines using Si photonics technology for telecom/datacom, and optical systems for XR applications. We have developed advanced expertise in precisely controlling the optical and physical properties of optical resins in the information and telecommunication field. In recent years, we have applied this expertise to the successful development of high heat resistant optical adhesives for solder reflow and high refractive index resins for XR optical systems. Here, we introduce our optical adhesives with small refractive index change of less than ±0.005 after baking at 260℃ for 5 minutes for Si photonics. We also present various types of resins with high refractive indices up to 2.0 for nanoimprint lithography and coatings.

In recent years, increasing attention has been devoted to OLEDs as a promising technology for general lighting. This application requires high brightness and thus higher drive current density than displays, reducing efficiency and lifetime to levels unsuitable for general illumination. To address this limitation, we are developing OLEDs deposited on corrugated substrates that increase the effective device area within the same module size, lowering the local current density at the same level of brightness. This talk discusses the fabrication approach to making devices on non-planar substrates, and the relationship between surface topography and OLED performance.

Graded-index plastic optical fiber (GI POF) with high bandwidth and excellent flexibility is a promising candidate for optical interconnects in applications such as data centers, automotives, and households. Recently, we have developed a novel GI POF that enables significantly low-noise data transmission by controlling light scattering properties through the microscopic heterogeneous structures formed in the fiber core material. This novel GI POF can contribute to energy saving and low latency in high-speed communication systems, especially in data centers, because of ultra-stable data transmission without the need for error correction techniques. In this talk, the recent progress of the GI POF technology is presented toward the upcoming Beyond 5G era.

Low-energy, infrared (IR) photodetection forms the foundation for industrial, scientific, energy, medical, and defense applications. State-of-the-art technologies suffer from limited modularity, intrinsic fragility, high-power consumption, require cooling, and are largely incompatible with integrated circuit technologies. Conjugated polymers offer low-cost and scalable fabrication, solution processability, room temperature operation, and other attributes that are not available using current technologies. Here, we demonstrate new materials and device paradigms that enable an understanding of emergent light-matter interactions and optical to electrical transduction of IR light. Photodiodes show a response to 2.0 μm, while photoconductors respond across the near- to long-wave infrared (1–14 µm). Fundamental investigations of polymer and device physics have resulted in improving performance to levels now matching commercial inorganic detectors. This is the longest wavelength light detected for organic materials and the performance exceeds graphene at longer wavelengths. Photoconductors outperform their inorganic counterparts and operate at room temperature with higher response speeds.

The traditional approach to manufacturing optical fibers with a microstructured cross-section is based on first fabricating a fiber preform in a multiple-stage procedure, and then drawing of the preform to fiber. These processes require the use of several dedicated and sophisticated equipment, including a fiber drawing tower. Here we demonstrate a simple, continuous, and low-cost approach to produce microstructured optical fibers in a single-step from the pellets of the optical material directly to the final fiber by using a commercial table-top filament extruder. This single-step fabrication procedure is time, electrical power, and floor space efficient. As proof-of-concept of the viability of this novel manufacturing approach, we demonstrate the fabrication of three different fiber geometries (hexagonal-lattice solid core, suspended core and hollow core) using Zeonex as the optical material. We also show the manufacture of an active optical fiber by using ABS polymer doped with luminescent Rhodamin dye. For all three fiber types, the microstructured geometry was evaluated. For the hollow core fiber, air guidance in a wavelength range where the fiber material is opaque was shown.

This study applies various ZnO thin films (sol-gel process based on high and low temperature and nanoparticle process) as electron extraction layer in inverted organic solar cells based on PBDB-T:ITIC, and the correlation between ZnO and solar cell performance was analyzed. When the ZnO thin film was formed by the high temperature(450°C) sol-gel process, the sheet resistance of ITO electrode was increased up to 5 times. As a result, the power conversion efficiency was low at 4.12%. In the nanoparticle process, butanol-based ZnO has better dispersion and surface properties than IPA-based ZnO, resulting in improved organic solar cell performance (PCE of 6.35% and 4.58% with butanol and IPA-based ZnO respectively). In addition, ZnO precursor solution with a low-temperature (150°C) sol-gel process was developed, and as a result of applying it as an electron extraction layer of an inverted organic solar cell, the device performance was greatly improved (PCE of 8.89%). The main reason for the improvement of the device performance is that the ripple-shaped surface is formed, which facilitates extraction of electrons and has excellent surface roughness.

The growing interest in fluorescent molecules capable of absorbing two photons has been driven by their significance in two-photon absorption (2PA) microscopy. However, challenges persist due to low 2PA in small molecules. Derivatives of dithienyl-diketopyrrolopyrrole (DPP2Ts) offer a solution with their easily modifiable nature, high fluorescence quantum yield, and structural planarity. In this work, two symmetric DPP2T derivatives were studied, exploring the influence of bromine on 2PA using the Z-scan technique. The results showed absorption in the near-infrared with a 1.4-fold increase in 2PA values (19-27 GM) due to the presence of bromine. However, bromine negatively affected emissive properties, reducing fluorescence from 73% to 56%. These findings hold promise for the utilization of DPP2Ts as fluorescent markers.

Organic π-conjugated molecules offer great potential for nonlinear optics applications due to their structural flexibility and favorable emissive properties. Diketopyrrolopyrrole (DPP) derivatives, known for their high planarity and excellent emissive properties, are particularly attractive for such research. In this study, we investigated excited state absorption (ESA) in two DPP derivatives with thienyl groups and different peripheral substituents (hydrogen and bromine) using Z-scan and pump-and-probe techniques. The presence of the bromine atom resulted in a significantly higher nonlinear response, as evidenced by an ESA band at 415 nm with a cross-section 15 times larger than the ground state. Additionally, the sample with bromine exhibited a twofold increase in the cross-section. These findings establish DPP derivatives as promising materials for photonic device applications.