This PDF file contains the front matter associated with SPIE Proceedings Volume 12418, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Synergetic ferroelectric luminescent (SFL) materials comprising a central tetraphenylethene (TP) core were synthesized by attaching TP with clipping groups (C), where clipping groups consist of a self-assembling group (SAG). TPCns selfassembled by the intermolecular interaction of SAGs to induce TP aggregation, as evidenced by the clip-induced quenching of emission at SAGs (E_clip) accompanied by aggregation-induced emission enhancement of TPs (E_AIE). TPC4 showed strong photoluminescence in a dilute chloroform solution and large E_AIE in aqueous (<50%) THF solution. TPCn film showed SFL properties with high quantum yield of photoluminescence (<80%) and ferroelectric switching. TPC4 was successfully employed in light emitting electrochemical cells (LECs) to achieve high luminance above 1290 cd m−2 under pulsed current conditions. TPC4 had a higher remnant polarization (Pr = 2.27 μC cm⁻²) at room temperature than TPC1. The thin film of TPCn was stable even with repeated bending due to the flexible SAG with long alkyl chains. Therefore, the SFL of TPCn was effectively employed in a piezoelectric nanogenerator, which produced piezoelectric output voltage of up to 0.13 V and a current density of 1.14 nA cm⁻² under repeated concave bending. These results indicate that side chain clipping and central TP aggregation resulted in unprecedented flexible SFL properties in a single compound, which simultaneously enhanced electroluminescence, mechanical sensitivity and energy harvesting ability.

Our laboratory has a long-standing interest in the structure, reactivity, and dynamics of free radicals in both homogeneous and heterogeneous media. In this presentation, the basic tenets of steady-state and time-resolved (CW) electron paramagnetic resonance spectroscopy (SSEPR and TREPR) are explained, and their use in understanding the physical and chemical behavior of free radicals is outlined. Examples to be presented include the use of stable nitroxide spin probes to investigate the drying and curing of architectural coatings, and to probe the physical properties of structured (non- Newtonian) fluids at the molecular level. Chemical reactivity involving free radicals can be studied directly using TREPR, for example in the study of the mechanism for the light-struck flavor (so-called “skunking”) of beer. Reactivity can also be investigated using spin trapping techniques. Two different trapping methods will be presented: nitrones can be used to confirm the mechanism of action of biocompatible polymer initiators, and the reaction of hindered amines with singlet oxygen can be used to quantify the kinetics and topology of such reactions in confined media. Finally, the application of EPR spectroscopy to study two aspects of polymer chain dynamics in liquid solution will be presented: 1) main chain radicals of acrylic polymers studied as a function of polymer structure and temperature, and 2) long-range radical-triplet state pair interactions in acrylic polymers.

Previous reports of chalcogenopyrylium polymethine dyes establish singlet oxygen yields as high as 12%. Our studies of these systems suggested that the current understanding of the excited state dynamics is incomplete. In fact, we observe no evidence for singlet oxygen generation across a range of experiments. We have carried out steady-state and pulsedlaser kinetic experiments on a family of fourteen dyes, including six novel dyes, selected to vary physical and electronic structure. We have changed the identity of the chalcogen between selenium and tellurium heteroatoms, phenyl, thiophene, tert-butyl substituents, and methine linker length. Excited-state lifetimes were obtained by femtosecond transient absorption spectroscopy. Lifetimes were all sub-300 picoseconds, suggesting rapid relaxation. Furthermore, we observed no evidence of any triplet transient processes; phosphorescence was only observed in samples at 77 K. Variable-temperature NMR experiments implicate rotation of the pyran ring about the methine backbone as a critical determinant of the dynamics of these dyes that distinguishes their photophysics from more rigid analogues.

Our group has developed cyclometalated iridium complexes as nonlinear optical materials, focusing especially on reversesaturable absorption (RSA). Cationic cyclometalated iridium complexes with isocyanide ancillary ligands offer several advantages in this context, elaborated in previous studies. This talk describes next-generation complexes of the general formula [Ir(C^N)₂(CNAr)₂]⁺, where C^N is a variable cyclometalating ligand and CNAr is a pyrene-decorated aryl isocyanide. In these compounds the dominant ground-state absorption transitions, especially in the visible range, are controlled by the C^N ligand. However, the lowest-energy triplet excited state (T₁) is typically located on the pyrene moiety, which has two consequences on the spectroscopic properties. First, these compounds exhibit temperaturedependent luminescence profiles. At room temperature, photoluminescence is mostly quenched by triplet energy transfer to the pyrene, and only residual pyrene fluorescence is observed. At low temperature (77 K), phosphorescence from the pyrene is turned on, and bright red luminescence is observed. The pyrene isocyanides also have profound impacts on the transient absorption spectroscopy of these compounds. Following visible excitation, a strongly absorbing, long-lived excited state is rapidly populated, which gives rise to ESA over the entire visible range and is assigned to the pyrene triplet state. The pyrene isocyanide complexes have higher excited-state absorption cross section (i.e. larger ΔOD) relative to first-generation complexes, and the excited-state lifetime increases by as much as an order of magnitude.

Equipping buildings with energy harvesting windows is a practical way to reduce greenhouse gas (GhG) emission. Utilizing semi-transparent organic photovoltaics (ST-OPVs) for this application requires the device to be colorfast, allowing for no change in the aesthetics or light harvesting property of the window. Here, we demonstrate an ST-OPV that is colorfast under 1 Sun AM 1.5G illumination at 50 0C and relative humidity of 34 %.

Hybrid organic electro-optic (OEO) modulators consist of aligned OEO chromophores confined in a metal or semiconductor slot waveguide, enabling optical fields to be tightly confined within the OEO material. The combination of tight confinement with the high electro-optic (EO) performance of state-of-the art OEO materials enables extraordinary EO modulation performance in silicon-organic hybrid (SOH) and plasmonic-organic hybrid (POH) device architectures. Recent records in POH devices include bandwidths < 500 GHz and energy efficiency < 100 aJ/bit. To enable commercial applications of these materials and devices, however, the materials integration processes must be finely tuned to afford excellent EO activity and long-term stability under demanding conditions, both during manufacture and operation. The conceptually simple design of POH devices affords a useful platform for process optimization, while the intense optical confinement provides an ideal environment to examine the photochemical stability of OEO materials in hybrid modulators. We have performed process optimization to obtain good EO performance with commercial and developmental OEO materials in POH devices, and examined the long-term operational and shelf storage stability of such devices under a variety of conditions relevant to Telecordia GR-468-CORE standards. We analyze the results of these studies and discuss their implications for commercial applications, including manufacturing, encapsulation requirements, and expected operational lifetimes.

In the field of light-responsive polymers, coumarin is one of the most commonly used structural motifs. By applying different wavelengths, materials' properties can be changed. Hereby, limited reversibility of the reaction is reported in many cases. By introducing a novel intramolecular coumarin dimer (ICD) based polymer architecture, the reversibility of the reaction is increased significantly. The photoreaction of the reversion and addition reaction is performed over several illumination cycles with alternating UV-wavelength light (λ = 265 nm for cycloreversion, λ = 345 nm for cycloaddition). A high degree of reversibility is reached by keeping the mobility low. Performing the illumination cycles at low temperatures and using a highly crosslinked material for structural confinement, the clean photochemical reaction path is maintained. Loss of the preferred molecular orientation, e.g. by heating, resembles the coumarin moieties, which results in non-defined photoreaction and decreased reversibility. By incorporating the ICD structure in different polymers, a bunch of applications are presented. Besides light-induced refractive index modulation, also fluorescence changes in polymer thin films were achieved. In addition, the cycloreversion reaction was performed under two-photon absorption (TPA) conditions using intense visible light laser pulses. For the TPA-induced reaction, a different reaction mechanism compared to the UV-light-induced reaction was found. The TPA-induced reaction offers great potential in further applications in the field of light-responsive polymers, e.g. for optical data storage or waveguide technologies.

We have investigated a select group of amorphous aromatic polyimides to determine their potential suitability in fabricating thermally stable optical components, intended for use at high temperatures. Compared to current commercial polymers, these polyimides have much higher glass transition and decomposition temperatures, and also have much lower thermo-optic and thermal expansion coefficients. This combination of characteristics makes them potentially useful in a wide range of commercial and military applications. To better understand the optical properties of these polyimides, we have investigated correlations between several aspects of their chemical structures and their thermo-optical properties. Our study consisted of synthesizing variations of these polyimides, which incorporated targeted structural modifications, and then correlating these structures with trends observed in their optical properties. The modifications studied included the substitution of a variety of side groups that affect the low-frequency vibrational modes, the substitution of structural isomers with distinct symmetries, and the introduction of functional groups that alter the monomer-level anisotropy. Furthermore, we also investigated copolymerization in compatible pairs of monomers as a means of fine-tuning the thermo-optical properties.

While Bragg grating-based optical devices have shown promising performances for pressure sensing applications, their sensitivity, especially in the low-pressure regime, is unsatisfying and needs to be optimized by elaborate designs, such as cantilevers or other extrinsic mechanical transducers. This contribution demonstrates and discusses a novel concept for optical pressure sensors based on polymer planar Bragg gratings. Waveguide and Bragg grating are fabricated underneath the surface of a temperature-stable and humidity-insensitive cyclic olefin copolymer substrate by means of a femtosecond laser. Based on the employed direct-writing procedure, in combination with adaptive, in-situ beam shaping with a spatial light modulator, writing depth, i.e., location of the photonic structures within the substrate, as well as Bragg grating periodicity and positioning can be deliberately chosen. Afterwards, the polymer substrate is post-processed with a highprecision micro mill, so a diaphragm comprising the integrated photonic structures is generated. The resulting diaphragm exhibits a thickness of 300 μm and a diameter of 10 mm. Finally, the optical sensor is packaged and sealed to form an airfilled gas pocket underneath the diaphragm. Deformations of the diaphragm by external pressure changes translate to strain variations along the waveguide axis and thus perturb the Bragg grating period. This leads to changes in the grating’s wavelength of main reflection, which can be evaluated in order to quantify the relative external pressure. With this straightforward optical sensor concept, pressure sensitivities up to 39 pm kPa-1, within relative pressures ranges from -78 kPa to 372 kPa, are achieved.

In many areas a spatially and temporally resolved measurement of the refractive index is desirable. This also applies to the additive manufacturing of optical components. Thereby the resulting refractive index of the optics to be printed depends on the degree of curing of the polymer. The latter is directly related to the UV radiation used. Here we want to introduce a measuring system based on total internal reflection, which can be used to measure the refractive index of a polymer during polymerization using a UV projection system. In detail the sample to be examined is located on a prism and can be cured using a DLP projection system. A laser beam is focused on the interface between the sample and the prism. Due to the focusing, light rays hit the sample from a certain angle range. Depending on the condition for total reflection, these light rays are either totally reflected or decoupled from the prism. By determining the critical angle, conclusions can be drawn about the refractive index of the sample. In this way a locally and temporally resolved image-based determination of the refractive index distribution is possible.

We demonstrate a simple and feasible procedure for the making of flexible multimode optical channel waveguides for light transmission in the visible and near-infrared region for biocompatible applications. The biocompatible optical elastomer with a refractive index of 1.427 was used for the core layer and the elastomer with a refractive index of 1.411 at wavelengths 654.2 nm was used for the cladding. The presented optical biocompatible silicone elastomers waveguides have appropriate properties with low optical losses. The average values of the optical losses were lower than -0.42 dB/cm at 650 nm, -0.40 dB/cm at 850 nm, -0.50 dB/cm at 1300 nm and -1.45 dB/cm at 1550 nm. This makes them suitable for realization not only in optical interconnection applications, sensors, micro-opto-electro-mechanical systems but also for optical waveguides in deep-tissue photomedicine.

The fast switchable electrochromic (EC) materials have strong interest for controlling unnecessary lights from environment or achieving color tunability in transmissive-type and reflective-type display. In this study, a black color tunability of electrochromic dimming device was explored using polyoxometalate (PW)-anchored metal oxide (MOx) nanoparticles, poly(3,3-bis(bromomethyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)s (PRBr), and an acid-free electrolyte layer. The PW-anchored MOx (PWMOx) layer was formed by electrostatic anchoring between the protonated MOx film and PW anion on a transparent electrode. The PWMOx was not only gave positive feedback to the electrochromic performance of its film, but also lowered the operating voltage by increasing the potential applied to the polymer layer in the electrochromic device, achieved black EC switching with high transparency modulation, a fast response time, and long endurance at a low operating voltage between 1.5 and -1.5 V. Furthermore, the boosted EC polymer properties arising from the charge balancing effect had the blocking capability for high-intensity light, such as 240 cd/m2 and ~ 2379 cd/m2 of light. The ECD blocked light transmission up to 95 % and dimming was adaptable to step voltage. This strategy may be coupled with various devices, including smart windows, transparent displays, image sensors, and augmented reality systems.