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1. New paradigms in materials and devices for hybrid electro-optics and optical rectification

   https://doi.org/10.1117/12.2595638  

   Johnson, Lewis E.; Elder, Delwin L.; Xu, Huajun; Hammond, Scott W.; Benight, Stephanie J.; O'Malley, Kevin; Robinson, Bruce H.; Dalton, Larry R. (August 2021, Molecular and Nano Machines IV)

   Sekkat, Zouheir; Omatsu, Takashige (Ed.)

   We review recent transformative advances in materials design, synthesis, and processing as well as device engineering for the utilization of organic materials in hybrid electro-optic (EO) and optical rectification (OR) technologies relevant to telecommunications, sensing, and computing. End-to-end (from molecules to systems) modeling methods utilizing multi-scale computation and theory permit prediction of the performance of novel materials in nanoscale device architectures including those involving plasmonic phenomena and architectures in which interfacial effects play a dominant role. Both EO and OR phenomenon require acentric organization of constituent active molecules. The incumbent methodology for achieving such organization is electric field poling, where chromophore shape, dipole moment, and conformational flexibility play dominant roles. Optimized chromophore design and control of the poling process has already led to record-setting advances in electro-optic performance, e.g., voltage-length performance of < 50 volt-micrometer, bandwidths > 500 GHz, and energy efficiency < 70 attojoule/bit. They have also led to increased thermal stability, low insertion loss and high signal quality (BER and SFDR). However, the limits of poling in the smallest nanophotonic devices—in which extraordinary optical field densities can be achieved—has stimulated development of alternatives based on covalent coupling of modern high-performance chromophores into ordered nanostructures. Covalent coupling enables higher performance, greater scalability, and greater stability and is especially suited for the latest nanoscale architectures. Recent developments in materials also facilitate a new technology—transparent photodetection based on optical rectification. OR does not involve electronic excitation, as is the case with conventional photodiodes, and as such represents a novel detection mechanism with a greatly reduced noise floor. OR already dominates at THz frequencies and recent advances will enable superior performance at GHz frequencies as well. 

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2. Birefringence, dimensionality, and surface influences on organic hybrid electro-optic performance

   https://doi.org/10.1117/12.2594939  

   Johnson, Lewis E.; Elder, Delwin L.; Benight, Stephanie J.; Tillack, Andreas F.; Hammond, Scott R.; Heni, Wolfgang; Dalton, Larry R.; Robinson, Bruce H. (August 2021, Physical Chemistry of Semiconductor Materials and Interfaces XX)

   Congreve, Daniel; Nielsen, Christian; Musser, Andrew J.; Baran, Derya (Ed.)

   Hybrid organic electro-optic (OEO) devices consist of a layer of ordered organic chromophores confined between layers of metals or semiconductors, 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 exceptional electro-optic switching 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. However, optimization of device performance requires both understanding and improving the degree to which chromophores can be acentrically ordered near a metal or semiconductor interface. Applying bulk and/or isotropic models of OEO materials to nanophotonic device architectures often lead to overly optimistic translation of materials performance to device performance. Prior work has identified influences of high centrosymmetric order (birefringence), altered relations between acentric and centrosymmetric order (dimensionality), and surface electrostatics on chromophore ordering. We combine these models into a representation that can be used to understand the influences of these phenomena on device performance, how some prior OEO materials exhibited unusually high performance under confinement, how ordering close to surfaces may be improved, and implications for future electro-optic device design. 

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3. Organic electro-optic materials combining extraordinary nonlinearity with exceptional stability to enable commercial applications

   https://doi.org/10.1117/12.2622099  

   Hammond, Scott R.; O'Malley, Kevin M.; Xu, Huajun; Elder, Delwin L.; Johnson, Lewis E. (March 2022, Organic Photonic Materials and Devices XXIV)

   Rau, Ileana; Sugihara, Okihiro; Shensky, William M. (Ed.)

   Hybrid organic electro-optic (OEO) modulators consist of a layer of ordered organic chromophores confined between layers of metals or semiconductors, 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, they must withstand demanding thermal and environmental conditions, both during manufacture and operation. To address these concerns, we examined the long-term thermal and environmental shelf storage stability of state-of-the-art commercial and developmental OEO materials under a variety of conditions relevant to Telecordia GR-468-CORE standards. We examined the shelf storage of poled OEO materials under a nitrogen atmosphere at a range of temperatures from 85 ̊C up to 150 ̊C to understand the kinetics of the thermally activated de-poling of the OEO materials. We also examined the shelf storage of OEO materials under a variety of atmospheres, including the aggressive 85 ̊C and 85% relative humidity damp heat condition, to understand the relative sensitivities of the materials to water and oxygen at different temperatures. We analyze the results of these studies and discuss their implications for commercial application of these materials and devices, including manufacturing, encapsulation requirements, and expected operational lifetimes. 

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4. Using sulfur bridge oxidation to control electronic coupling and photochemistry in covalent anthracene dimers

   https://doi.org/10.1039/C8SC05598J  

   Cruz, Chad D.; Yuan, Jennifer; Climent, Clàudia; Tierce, Nathan T.; Christensen, Peter R.; Chronister, Eric L.; Casanova, David; Wolf, Michael O.; Bardeen, Christopher J. (January 2019, Chemical Science)

   Covalently tethered bichromophores provide an ideal proving ground to develop strategies for controlling excited state behavior in chromophore assemblies. In this work, optical spectroscopy and electronic structure theory are combined to demonstrate that the oxidation state of a sulfur linker between anthracene chromophores gives control over not only the photophysics but also the photochemistry of the molecules. Altering the oxidation state of the sulfur linker does not change the geometry between chromophores, allowing electronic effects between chromophores to be isolated. Previously, we showed that excitonic states in sulfur-bridged terthiophene dimers were modulated by electronic screening of the sulfur lone pairs, but that the sulfur orbitals were not directly involved in these states. In the bridged anthracene dimers that are the subject of the current paper, the atomic orbitals of the unoxidized S linker can actively mix with the anthracene molecular orbitals to form new electronic states with enhanced charge transfer character, different excitonic coupling, and rapid (sub-nanosecond) intersystem crossing that depends on solvent polarity. However, the fully oxidized SO 2 bridge restores purely through-space electronic coupling between anthracene chromophores and inhibits intersystem crossing. Photoexcitation leads to either internal conversion on a sub-20 picosecond timescale, or to the creation of a long-lived emissive state that is the likely precursor of the intramolecular [4 + 4] photodimerization. These results illustrate how chemical modification of a single atom in the covalent bridge can dramatically alter not only the photophysics but also the photochemistry of molecules. 

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5. Linear scaling relationships in homogeneous photoredox catalysis

   https://doi.org/10.1039/D4RE00419A  

   Kron, Kareesa J; Mallikarjun_Sharada, Shaama (November 2024, Reaction Chemistry & Engineering)

   In the photoredox catalytic cycle of CO₂reduction with organic chromophores, this work observes a linear relationship between the energies of (desirable) electron transfer to CO₂and (undesirable) carboxylation of the chromophore radical anion. 

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