This PDF file contains the front matter associated with SPIE Proceedings Volume 11683

Introduction to SPIE Photonics West OPTO conference 11683: Organic Photonic Materials and Devices XXIII.

Organic electro-optic (EO) polymers have attracted much attention to their potential use of the optical interconnection for faster data communication. Photochemical stability is a crucial problem to be solved for using in commercial systems. We investigated the photochemical stability of the EO polymers under irradiation of a laser at the O-band (1310 nm) to reveal the factors of photodegradation and to obtain a good estimate for the operating lifetime of the devices. Based on the results obtained, we will discuss the effects of excited singlet oxygen on the photochemical stability of the EO polymers.

In Beyond 5G wireless communication, it is expected that the radio over fiber (RoF) technology that transmits signal waveforms of terahertz waves (0.1-10 THz) using optical fibers will be important. In this research, we fabricated optical modulators consisting of the patch antenna arrays and electro-optic (EO) polymer waveguides, aiming to develop a device that directly modulates light by irradiating electromagnetic waves in the W band (75-110 GHz). We also prototyped a device structure with a ground electrode to improve the efficiency of the electromagnetic wave detection.

Stark effect is usually ignored because large effect is observed only at a wavelength where absorption is large. However, we found that contribution of the Stark effect is not negligible in the measurement of EO coefficient r even at a wavelength where the absorption is relatively small. Large Stark effect is useful for terahertz (THz) wave detection. The advantages of THz wave detection by the Stark effect is the wide bandwidth and simple optical geometry. Utilizing the Stark effect in EO polymers provides us with a wide variety of applications for electromagnetic wave detection.

This paper will review the use of nucleobases for optoelectronic applications. Nucleobases possess unique electromagnetic, optical, mechanical and thermal properties, including low optical loss and simultaneous low electrical resistivity, high temperature stability and a strong resistance to organic solvents. They are also hydrophobic, providing excellent hermetic sealing. They can be vapor deposited for a number of applications. Nucleobases have highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels suitable for charge blocking layers in organic light emitting diodes (OLEDs) and nonlinear polymer electro-optic modulators. With their low optical loss, they may prove suitable for optical waveguiding applications.

Many techniques on holographic mass storage systems have been developed, which scalar and vector optical data are stored in holographic materials. To realize high data transfer rate, binary SLM such as a ferroelectric liquid crystal SLM and a digital micro-mirror device (DMD). Therefore, methods to increase the recording density using binary data pages are proposed. The principles of the method are verified by numerical analysis and experimentsTwo shot recording for 4-level phase multiplexing is performed by a high-speed binary intensity SLM using a ferroelectric liquid crystal (FLC). Experimental results are presented in terms of recording capacity.

Miniaturized optical diagnostics might be greatly favored by the availability of effective, conformable UV light sources combining reduced size with mechanical flexibility. Here we report on our recent results on ZnO-incorporated nanofibers, exhibiting optical gain and polarized emission, used to obtain flexible UV lasers operating at room-temperature. The research leading to these results has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 682157, “xPRINT”), from the Italian Minister of University and Research (PRIN 2017PHRM8X) and from the University of Pisa (PRA “ANISE”).

Azobenzene is capable of reversibly switching its conformation upon the UV/Visible optical exposure due to its reversible trans/cis photoisomerization. By merging this organic material with conventional photonic devices, new architectures can be developed. In our study, we developed hybrid organic/inorganic whispering gallery mode microcavities consisting of a self-assembled 4-(4-diethylaminophenylazo)pyridine (Aazo) monolayer anchored on an integrated SiO₂ optical microtoroid. As the Aazo monolayer changed conformations, the resonant wavelength was tuned. The surface density of Aazo was modified by introducing CH₃ spacer molecules providing control over the magnitude of the shift. Owing to the uniformity of Aazo monolayer, cavity quality factors reached above 1 million in the near-IR range. Two optical lasers were simultaneously coupled into the Aazo-coated devices with a single waveguide. The 1300 nm laser is used to excite and monitor a single resonant wavelength of the cavity, and the 410 nm laser triggers the thermodynamically stable trans-Aazo to photoswitch to the thermodynamically unfavored cis-Aazo. When the Aazo photoswitches, the cavity resonant wavelength at near-IR wavelength shifts due to a change of refractive index in the Aazo layer. To revert the molecule back to trans-Aazo, a CO₂ laser is used to heat the device system. Even after storage in air, the switching behavior is unchanged. Theoretical analyses are conducted based on density functional theory of the Aazo isomers combined with finite element method simulations of the optical mode. The theoretical results agree with the experimental findings.

We reported Ag deposition-based electrochromic device which showed reversible color change from transparent to chromatic coloration, black and silver-mirror in a single device. This device newly enabled us to achieve multi-coloration including CMY and RGB. We analyzed relationship between optical properties and morphology of silver nanoparticles toward plasmonic nanophotonics.

The contribution describes the inkjet printing of 3D-optical components and systems, based on the hybrid polymer ORMOCER®, which exhibits not only good optical, but also excellent stability parameters versus environmental conditions such as temperature or radiation. With repeating the printing and UV-curing of single printed layers multiple times, a 3D-shape is formed out of thousands of individual layers. To increase the transmission of the 3D-printed optics a tailored AR-plas® one-step plasma treatment was developed. By varying the plasma parameters, the increase of transmission can be tailored within the whole visible spectrum and thus the overall transmission can be increased from 90% to more than 97%. This ensures the additive manufacturing of individualized 3D-optics with very high performance.

Here we will review our current activities on the realization of photonic active structures based on biomaterials. Nanofibers of DNA incorporating light-emitting chromophores are reported with enhanced optical emission and lasing properties tailorable by the fiber size and architecture. The research leading to these results has received funding the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 682157, “xPRINT”) and from the Italian Minister of University and Research through the PRIN 201795SBA3 project.

Numerous oxazole-based fluorophores show efficient emission in the UV and deep blue spectral range in the solid state, making them interesting candidates for use as emissive layers in organic light-emitting diodes (OLEDs). Three ozazole derivatives, i.e. 2-(p-tert-butylphenyl)benzoxazole (Bzx), 2-phenyl-naphthoxazole (Nzx) and 2,2’-di(p-tert-butylphenyl)- 6,6’-bibenzoxazole (BBzx), were used in OLEDs with neat films configurations. These molecules differ by their planarity, steric hindrance and size of the π-conjugated system. No photoluminescence was observed with Bzx and Nzx. In contrast, the incorporation of the bis-chromophore BBzx within thin solid films led to efficient emission. The corresponding OLEDs displayed a deep blue emission at 430 nm arising from the BBzx layer, with CIE coordinate of (0.157, 0.044). These specific optical features were attributed to the twisted molecular structure of the bis-chromophore, leading to reduction of the aggregation induced fluorescence quenching. An EQE of 1.2% was achieved with a driving current of 24 A/m². The results suggest that BBzx derivatives may be useful as efficient color saturation deep-blue emitters in OLEDs.

Thermally-activated delayed fluorescence (TADF) organic molecules undergo more efficient light emission than traditional organic fluorescent emitters, making them attractive materials for OLEDs. In TADF OLEDs, indirect emission from dark triplet states via bright singlet excitons is activated and leads to boosted electroluminescence efficiencies. Most studies of TADF use optical spectroscopies that can examine the photophysics and interconversion rates, but do not shed light on the critical spin physics. Here we use transient electron spin resonance spectroscopy to study triplet states involved in TADF and the role of hyperfine and spin-vibronic couplings on the critical singlet-triplet intersystem crossing for efficient TADF.

Long-lived room temperature phosphorescence from organic molecular crystals has attracted great attention owing to potential applications in organic electronics, information storage, and biotechnologies. The features of the persistent luminescence strongly depend on the electronic properties of the individual molecules, and on their molecular packing in the crystal lattice. Here, a new strategy is developed by rationally designing phosphors incorporating and combining for the first time a bridge for sigma-conjugation and a moiety for H-bond-directed supramolecular self-assembly. The molecular crystals exhibit room temperature phosphorescence quantum yields that reach up to 20% and lifetimes up to 520 ms. This study provides a promising strategy for the development of molecular crystals exhibiting efficient long-lived room temperature phosphorescence.

Metaphotonics is a rapidly emerging new direction that deals with manipulation of electric and magnetic fields and their coupling in (thin)nanoengineered materials to control the field distribution and propagation of electromagnetic waves1,2 Chiral photonics expands the scope of Metaphotonics and offers chiral control of both linear and nonlinear optical functions for applications ranging from optical switching, to negative- and near-zero refractive index metamaterials, to chiral bioimaging. However, realization of such applications requires materials with optical chirality at visible wavelengths that is orders of magnitude larger than that of any naturally-occurring materials. Our theory-guided-design and synthesis of novel chiral polymers with very large optical rotation will be presented along with our recent reports of plasmonic, excitonic and structural enhancement of linear and nonlinear optical activity. Some results on nanocomposite exhibiting large magneto-optic effect will also be presented, which may enable mapping of ultra-weak magnetic fields, like those generated by brain function. We are pursuing multiscale modeling and experimental design on interaction of structured light endowed with both spin and orbital angular momentum, with structured chiral plasmonic media for adaptive control of effective dielectric function which reveals that the incident light can be controlled dynamically, i.e. in terms of amplitude, wavelength, and total angular momentum, j (polarization and wavefront) to enable adaptive control of epsilon-near-zero behavior.

At optical spectral range where the real part of dielectric constant epsilon is near zero, optical processes are very distinct since phase velocity of optical wave is very large, leading to a low group velocity. After introducing a series of epsilon-near-zero organic materials, several examples of linear and nonlinear optical process in organic epsilon-near-zero organics will be presented. In particular, quadratic and cubic processes such as electro-optic effect, second-harmonic generation, and intensity-dependent refractive index and absorption will be discussed.

Third-order nonlinear optical response is shown to be enhanced near epsilon near zero (ENZ) spectral position. Regarding the materials exhibiting ENZ property, examples are reported such as hyperbolic metamaterial, inorganic oxides, nitrides, and organic monolithic hyperbolic thin film. By adopting series of organic thin films possessing ENZ property, we investigated second-order nonlinear optical process of electro-optic effect. When organic films are prepared in the order of several tens of nanometers thickness, a symmetry breaking takes place at the interface of organic thin film and substrate, allowing for second-order nonlinear optical responses of second harmonic generation and electro-optic (EO) effect. The presence of epsilon near pole (ENP) leads to an enhanced EO effect. The experimental results showed that the EO response is strongly enhanced in the spectral region of ENP associated with the existence of ENZ.

Transient and smart functionalities can be obtained by devices that can physically disappear in a controlled way. Water-soluble polymers and materials that can dissolve/disintegrate offer self-degradable opportunities for use in various domains. Here we report on our recent results on combinatory, transient photonics based on water-soluble compounds and sublimating materials for application in full-field imaging and labelling. The research leading to these results has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 682157, “xPRINT”) and from the Italian Minister of University and Research PRIN 20173L7W8K project.

Cyclometalated iridium complexes have long been prominent in electroluminescent applications, and several recent studies have shown that this family of compounds offers several potential advantages for designing materials with reversesaturable absorption (RSA) and other nonlinear optical properties. In this talk we present a comprehensive study of the excited-state properties of three bis-cyclometalated iridium complexes of the general formula [Ir(C^N)₂(CN^dmp)₂]⁺, where C^N is a variable cyclometalating ligand and CN^dmp is 2,6-dimethylisocyanide. The ground-state absorption and photoluminescence (PL) properties are described, with the identity of the cyclometalating ligand having a large effect on the observed PL wavelength. When the cyclometalating ligand is 2-phenylbenzothiazole (pbt), intense yellow PL is observed, whereas the PL with nitro-substituted 9-pyridylphenanthrene or 2-phenylpyridine C^N ligands is red-shifted and much weaker. Transient absorption (TA) spectroscopy was used to evaluate the excited-state absorption of the compounds. TA spectra indicate broad and intense excited-state absorption for all three compounds, with the wavelength profile strongly determined by the cyclometalating ligand. TA lifetimes are consistent with PL lifetimes and strongly oxygendependent, indicating that excited-state absorption that arises from a triplet state. To evaluate the effects of the CN^dmp isocyanide ancillary ligands, we include comparisons to charge-neutral Ir(C^N)₂(acac) (acac = acetylacetonate) complexes with the same C^N ligands. The isocyanide compounds have substantially blue-shifted ground-state absorption, excitedstate absorption, and PL, and in most cases longer lifetimes compared to the acac analogues.

Transition metal chromophores (TMCs) are a widely studied class of materials due to their synthetic tunability and photophysical properties. Second- and third-row d⁶ TMCs, such as Ru^II or Ir^III, are of particular importance due to their large spin-orbit coupling constants and the prevalence of metal-to-ligand charge transfer (MLCT) excited states. TMCs have found broad application in organic light-emitting diodes (OLEDs), photoredox catalysis, photodynamic therapy, and non-linear optics (NLO). Recent photophysical studies on organometallic iridium complexes of the form [Ir^III(C^N)₂(acac)]⁰, where C^N is a cyclometalating ligand and acac is acetylacetonate, have demonstrated their potential as reverse saturable absorption (RSA) materials. The photophysical properties, including photoluminescence and transient absorption spectra, are reported for [Ir(pbt)₂(acac)], where pbt is 2-phenylbenzothiazole. In an attempt to engender new excited state absorption (ESA) bands, a triphenylamine (TPA) moiety was installed on the pbt ligand via microwave-assisted Suzuki coupling. The spectroscopic properties of the new TMC were compared to the parent [Ir(pbt)₂(acac)] complex with particular emphasis on their potential application as RSA materials.

Coordination-driven self-assembly is a synthetic method that uses metal-ligand bonding as the driving force for the formation of polynuclear metallacycles and cages. These discrete molecules may exhibit so-called emergent properties, wherein the proximity of building blocks results in novel electronic structure and related photophysical properties. Selfassembly reactions using iridium complexes as metal nodes and organic molecules as linkers generates a library of metallacycles and cages containing multiple chromophores. These architectures preserve the promising photochemistry of the monomeric Ir centers found at the nodes in the context of organic light-emitting diodes and non-linear optical applications such as reverse saturable absorption. The design and characterization of a small library of platinum and iridium assemblies is presented with an emphasis on understanding the differences between the properties of the independent building blocks and those of the assemblies.

In this study, the effect of exciton-blocking layer (EBL), employed between the electron-transporting layer (ETL) and the undoped host spacer layer, on the characteristics of fluorescent/phosphorescent multilayer white organic lightemitting diode (OLED) is investigated numerically with the APSYS (Advanced Physical Model of Semiconductor Devices) simulation program. The validation of simulation model is confirmed by the good agreement of photoelectric characteristics between the results obtained numerically and those obtained experimentally. Simulation results suggest that singlet excitons and triplet excitons are generated at both hole-transporting layer (HTL)/emitting layer (EML) and EML/ETL interfaces, where electrons and holes accumulate and recombine, with certain thickness of host spacer layers employed on both sides of EML of white OLED structure. Further study shows that a better choice for the trade-off between color stability and electroluminescence (EL) efficiency can be achieved by properly adjusting the number of EBLs. An optimized performance is achieved if two pairs of EBLs are used.

The phenomenon of vector polyphotochromism was found earlier in some high-efficient polarization-sensitive materials depending on the radiant exposure of the inducing linearly polarized actinic light. This effect was observed at high radiant exposures. In this paper the vector polyphotochromic effect is considered when azimuthally dependent exposure is used. The principal difference in these two approaches is that, in exposure-dependent technique, the transmission spectrum of the material depends on the magnitude of the inducing light exposure and this dependence is non-linear. Therefore, certain tunable spectral profiles of the material are very difficult to be fixed, in particular, in the blue spectral region. In the use of the azimuthally dependent technique, the changes in the transmission spectrum are occurred depending on the polarization azimuth of the inducing light. It is shown that the advantage of this approach is the possibility of inducing this effect at much lower exposures of the exciting radiation and obtaining approximately linear dependence of the spectral characteristics of the material on illumination conditions. It should be noted the material used exhibits photochromic behavior of an unusual nature, which is based not on a slight change in the spectral characteristics of the pigment under the light action, but there are changes in the so-called interference color of the medium as a result of selective quenching the corresponding regions of the transmission spectrum of the given material. The polarizationsensitive materials based on biopolymer matrix and organic azo dyes have been used. The obtained results can be used for creating spectral-selective polarization element with high-speed.