Molecule-based electrooptic (EO) materials are of intense research interest for understanding how light interacts with matter and for applications in photonic technologies such as high-speed optical communications, integrated optics, and optical data processing and storage. [1] In such materials, the second-order susceptibility tensor governing EO response (r 33 ), is governed both by the net polar microstructural order and the microscopic molecular first hyperpolarizability tensor (b). Large b values are essential for large EO response, and the quest for higher performance EO chromophores presents a daunting challenge.[1] To date, effective chromophores have been designed according to similar principles embodied in the classical "two-level" model: conjugated p systems endcapped with donor (D) and acceptor (A) moieties.[2] Elegant efforts have sought maximum b by optimizing D and A strengths and conjugation pathways, [3] directed by "bond length alternation" [4] and "auxiliary donor and acceptor" models.[5] Such strategies utilize extended planar p-conjugation, resulting in chromophores that are inherently elaborate structurally, complicating synthesis and introducing potential chemical, thermal, and photochemical instabilities.[6] Alternative routes to very large-b chromophores would clearly be desirable, and there is growing evidence that simple two-level systems may not provide access. [7] Recent theoretical work suggests that unconventional chromophores with twisted p-electron systems bridging D and A substituents (TICTOID = twisted intramolecular chargetransfer; Scheme 1) may exhibit unprecedented hyperpolarizabilities through non-classical mechanisms.[8] These would have relatively simple biaryl structures in which b is sterically tunable through R 1 , R 2 modification of the interplanar dihedral angle (q). Large b magnitudes are predicted at q % 70-858, [8a] with twist-induced reduction in D-p-A conjugation leading to charge-separated zwitterionic ground states. The intriguing question is whether such molecules, with small numbers of p-electrons, could thereby exhibit far larger b values than conventional planar chromophores.We report here the first realization of such TICTOID chromophores, that they have unprecedented hyperpolarizabilities on the order of 10-20 larger than previously observed, [1][2][3][4][5] and that these are not simple two-level systems. The new chromophores (Scheme 1) were designed according to the following criteria: 1) Synthetically challenging tetraortho-alkylbiaryl cores should enforce large interplanar angles, judging from bimesityl (q % 908).[9] 2) Dicyanomethanide and pyridinium groups should be effective D and A substituents, with dicyanomethanide more stable than phenoxide.[10] 3) Pyridine alkylations should enhance solubility and processability (TMC-1 and TMC-2), with styrenic substitution further enhancing b (TMC-2).TMC syntheses (Scheme 2) begin with precursor 1, synthesized as reported elsewhere. [10] Pd-catalyzed NaCH(CN) 2 coupling affords 2, which is then regioselect...

Organic light-emitting diodes (OLEDs) fabricated on flexible plastic substrates are the focus of increasing attention due to their broad potential applications in portable devices such as cellular phones, personal digital assistants (PDAs), and laptops, etc., which require light weight and mechanical durability. [1,2] Heeger and co-workers first reported flexible OLEDs, fabricated from a conducting polymer electrode deposited on poly(ethylene terephthalate) (PET).[3] It was generally thought at the time that mechanical flexibility could only be achieved with a polymeric electrode. However, Forrest and co-workers subsequently demonstrated flexible, vacuum-deposited, small-molecule OLEDs fabricated on indium tin oxide (ITO)-coated PET and having the structure PET/ITO/ TPD/Alq/MgAg/AgÐanalogous to those of conventional glass-based devices, and capable of repeated flexing.[4] Subsequently, small-molecule OLEDs have been fabricated on several kinds of plastic or plastic/inorganic hybrid substrates, pre-coated with a transparent conductive oxide (TCO) such as ITO, by conventional pulsed-laser deposition or sputtering. [2,5,6] TCO growth on plastic remains a significant challenge for the fabrication of truly efficient flexible OLEDs, due to the poor thermal and mechanical properties of typical polymeric substrates. This is illustrated in ITO film growth on glass, where relatively high deposition and/or post-annealing temperatures (>200 C) are typically required to achieve reasonable electrical conductivity, optical transparency, and longterm stability. Conventionally, ITO film growth on plastic has been achieved by low-temperature deposition techniques such as sputtering. However, such films are typically amorphous, leading to poor conductivity, transparency, and adhesion properties, and underscoring the need for an improved growth technique. In contrast to simple sputtering, ion-assisted deposition (IAD) is uniquely suited for producing smooth, adherent, and microstructurally dense thin oxide films at remarkably low temperatures.[7] IAD employs two ion beams to effect simultaneous film deposition, oxidation, and crystallization, resulting in smooth, dense, coherent films at low temperatures. In addition, the assisting ion bombardment generates fresh surfaces during the pre-and in-situ cleaning/activation process, creating strong interfacial adhesion and removal of voids that can trap loosely bound/physisorbed O 2 , which may degrade OLED performance. These attractions raise the interesting question of whether IAD could be effectively employed in low-temperature ITO depositions for OLEDs, especially on plastics, because ITO's physical properties, such as work function, conductivity, morphology, and surface composition, etc., which significantly influence OLED performance, are strongly dependent on the specific deposition process and post-treatment. [8] To date, there have been no reports of OLED fabrication with IAD-deposited ITO. [9] We report here the growth and characteristics of high-quality ITO thin films on bo...

Highly near-infrared ͑NIR͒ transparent In 2 O 3 thin films have been grown by ion-assisted deposition at room temperature, and the optical and electrical properties characterized. NIR transparency and the plasma edge frequency can be engineered by control of the film deposition conditions. As-deposited In 2 O 3 thin films were employed as transparent electrodes for direct thin film electro-optic ͑EO͒ characterization measurements via the Teng-Man technique. Using LiNbO 3 as the standard, the relationship between electrode NIR transparency and Teng-Man EO measurement accuracy was evaluated. It is found that In 2 O 3 electrodes can be tailored to be highly NIR transparent, thus providing far more accurate Teng-Man EO coefficient quantification than tin-doped indium oxide. In addition, the EO coefficients of stilbazolium-based self-assembled superlattice thin films were directly determined for the first time using an optimized In 2 O 3 electrode. EO coefficients r 33 of 42.2, 13.1, and 6.4 pm/ V are obtained at 633, 1064, and 1310 nm, respectively.

An "X-shaped" two-dimensional electrooptic (EO) chromophore with extended orthogonal conjugation was designed and synthesized. Self-assembled thin films of this chromophore were fabricated via layer-by-layer chemisorptive siloxane-based self-assembly. The films exhibit a dramatically blue-shifted optical maximum (325 nm) while maintaining a large EO response (chi33(2) approximately 232 pm/V at 1064 nm; r33 approximately 43 pm/V at 1550 nm).

Molecule-based electrooptic (EO) materials are of intense research interest for understanding how light interacts with matter and for applications in photonic technologies such as high-speed optical communications, integrated optics, and optical data processing and storage. [1] In such materials, the second-order susceptibility tensor governing EO response (r 33 ), is governed both by the net polar microstructural order and the microscopic molecular first hyperpolarizability tensor (b). Large b values are essential for large EO response, and the quest for higher performance EO chromophores presents a daunting challenge.[1] To date, effective chromophores have been designed according to similar principles embodied in the classical "two-level" model: conjugated p systems endcapped with donor (D) and acceptor (A) moieties.[2] Elegant efforts have sought maximum b by optimizing D and A strengths and conjugation pathways, [3] directed by "bond length alternation" [4] and "auxiliary donor and acceptor" models.[5] Such strategies utilize extended planar p-conjugation, resulting in chromophores that are inherently elaborate structurally, complicating synthesis and introducing potential chemical, thermal, and photochemical instabilities.[6] Alternative routes to very large-b chromophores would clearly be desirable, and there is growing evidence that simple two-level systems may not provide access. [7] Recent theoretical work suggests that unconventional chromophores with twisted p-electron systems bridging D and A substituents (TICTOID = twisted intramolecular chargetransfer; Scheme 1) may exhibit unprecedented hyperpolarizabilities through non-classical mechanisms.[8] These would have relatively simple biaryl structures in which b is sterically tunable through R 1 , R 2 modification of the interplanar dihedral angle (q). Large b magnitudes are predicted at q % 70-858, [8a] with twist-induced reduction in D-p-A conjugation leading to charge-separated zwitterionic ground states. The intriguing question is whether such molecules, with small numbers of p-electrons, could thereby exhibit far larger b values than conventional planar chromophores.We report here the first realization of such TICTOID chromophores, that they have unprecedented hyperpolarizabilities on the order of 10-20 larger than previously observed, [1][2][3][4][5] and that these are not simple two-level systems. The new chromophores (Scheme 1) were designed according to the following criteria: 1) Synthetically challenging tetraortho-alkylbiaryl cores should enforce large interplanar angles, judging from bimesityl (q % 908).[9] 2) Dicyanomethanide and pyridinium groups should be effective D and A substituents, with dicyanomethanide more stable than phenoxide.[10] 3) Pyridine alkylations should enhance solubility and processability (TMC-1 and TMC-2), with styrenic substitution further enhancing b (TMC-2).TMC syntheses (Scheme 2) begin with precursor 1, synthesized as reported elsewhere. [10] Pd-catalyzed NaCH(CN) 2 coupling affords 2, which is then regioselect...

The efficient manipulation of light-matter interactions in subwavelength all-dielectric nanostructures offers a unique opportunity for the design of novel low-loss visible- and telecom-range nanoantennas for light routing applications. Several studies have achieved longitudinal and transverse light scattering with a proper amplitude and phase balance among the multipole moments excited in dielectric nanoantennas. However, they only involve the interaction between electric dipole, magnetic dipole, and up to the electric quadrupole. Here, we extend and demonstrate a unidirectional transverse light scattering in a V-shaped silicon nanoantenna that involves the balance up to the magnetic quadrupole moment. Based on the long-wavelength approximation and exact multipole decomposition analysis, we find the interference conditions needed for near-unity unidirectional transverse light scattering along with near-zero scattering in the opposite direction. These interference conditions involve relative amplitude and phases of the electromagnetic dipoles and quadrupoles supported by the silicon nanoantenna. The conditions can be applied for the development of either polarization- or wavelength- dependent light routing on a V-shaped silicon and plasmonic nanoantennas.

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