High-Performance Supramolecular Organogel Adhesives for Antimicrobial Applications in Diverse Conditions.

Supramolecular organogel coatings that can disinfect the deposited microbial pathogens are emerging as an effective vehicle to prevent pathogen transmission. However, the development of anti-pathogen supramolecular adhesives with mechanical robustness and controlled oil inclusion is technically challenging. Here, we report supramolecular adhesives with mechanical integrity and robust interfacial adhesion over a wide range of biogenic antimicrobial oil. Bifunctional monomers are synthesized and assembled into linear polymers with semicrystalline stackings through hierarchical hydrogen bonds, where incorporated bioactive oil could regulate the semicrystalline stackings into nanosized crystalline domains through intermolecular hydrogen bonds. The abundant bonding motifs provided by the supramolecular cross-linked networks could accommodate oil molecules with high inclusion capability and provide more interfacial binding sites with high adhesion strength, and the nanosized crystalline domains could stabilize the organogel network and compensate for the interactions with oil molecules to enhance structural and mechanical stability. In addition, rapid healing, robust adhesion, and antimicrobial and antiviral properties of the resultant organogel coatings are demonstrated. This study paves the way for the development of high-performance antimicrobial supramolecular adhesives with controlled oil inclusion, showing potential applications in soft robotics, tissue engineering, and biomedical devices.

Push-Pull Heptamethines Near the Cyanine Limit Exhibiting Large Quadratic Electro-Optic Effect.

Harnessing the quadratic electro-optic (QEO) of near-infrared polymethine chromophores over broad telecom wavelength bands is a subject of immense potential but remains largely under-investigated. Herein a series of push-pull heptamethines containing the tricyanofuran (TCF) acceptors and indoline or benzo[e]indoline donors are reported. These dipolar chromophores can attain a highly delocalized "cyanine-like" electronic ground state in solvents spanning a wide range of polarities, in some cases even closer to the ideal polymethine state than symmetrical cyanines. A transmission-mode electromodulation spectroscopy is used to study the electric-field-induced changes in optical absorption and refraction of polymer films doped with heptamethine chromophores, and large and thermally stable QEO effect with high efficiency-loss figure-of-merits that compare favorably to those from dipolar polyenes in poled or unpoled polymers and III-V semiconductors is obtained. The study opens a path for developing organic materials based on cyanine-like merocyanines for complementary metal oxide semiconductor -compatible, fast, efficient, and low-loss electro-optic modulation.

Intramolecular Chloro-Sulfur Interaction and Asymmetric Side-Chain Isomerization to Balance Crystallinity and Miscibility in All-Small-Molecule Solar Cells.

Intramolecular Cl-S non-covalent interaction is introduced to modify molecular backbone of a benzodithiophene terthiophene rhodamine (BTR) benchmark structure, helping planarize and rigidify the molecular framework for improving charge transport. Theoretical simulations and temperature-variable NMR experiments clearly validate the existence of Cl-S non-covalent interaction in two designed chlorinated donors and explain its important role in enhancing planarity and rigidity of the molecules for enhancing their crystallinity. The asymmetric isomerization of side-chains further optimizes the molecular orientation and surface energy to strike a balance between its crystallinity and miscibility. This carefully manipulated molecular design helps result in increased carrier mobility and suppressed charge recombination to obtain simultaneously enhanced short-circuit current (Jsc ) and fill factor (FF) and a very high efficiency of 15.73 % in binary all-small-molecule organic solar cells.

Ultrastretchable conductive liquid metal composites enabled by adaptive interfacial polarization.

Gallium-based liquid metals (LMs) are emerging candidates for the development of metal/polymer-based flexible circuits in wearable electronics. However, the high surface energies of LMs make them easily depleted from the polymer matrix and therefore substantially suppress the stretchability of the conductive composites. Here, we reveal that a dynamic interplay between the LM and the polyvinylidene fluoride (PVDF) copolymer can help to address these issues. Weak and abundant interfacial polarization interactions between the PVDF copolymer and the oxide layer allow continuous and adaptive configuration of the compartmented LM channels, enabling ultra-stretchability of the composites. The conductive LM-polymer composites can maintain their structural integrity with a high surface conductivity and small resistance changes under large strains from 1000% to 10 000%. Taking advantage of their flexible processability under mild conditions and exceptional performance, our design strategy allows the scalable fabrication of conductive LM-polymer composites for a range of applications in wearable devices and sensors.

Photochemical Synthesis of Nonplanar Small Molecules with Ultrafast Nonradiative Decay for Highly Efficient Phototheranostics.

There has been much recent progress in the development of photothermal agents (PTAs) for biomedical and energy applications. Synthesis of organic PTAs typically involves noble metal catalysts and high temperatures. On the other hand, photochemical synthesis, as an alternative and green chemical technology, has obvious merits such as low cost, energy efficiency, and high yields. However, photochemical reactions have rarely been employed for the synthesis of PTAs. Herein, a facile and high-yield photochemical reaction is exploited for synthesizing nonplanar small molecules (NSMs) containing strong Michler's base donors and a tricyanoquinodimethane acceptor as high-performance PTAs. The synthesized NSMs show interesting photophysical properties including good absorption for photons of over 1000 nm wavelength, high near-infrared extinction coefficients, and excellent photothermal performance. Upon assembling the NSMs into nanoparticles (NSMN), they exhibit good biocompatibility, high photostability, and excellent photothermal conversion efficiency of 75%. Excited-state dynamic studies reveal that the NSMN has ultrafast nonradiative decay after photoexcitation. With these unique properties, the NSMN achieves efficient in vivo photoacoustic imaging and photothermal tumor ablation. This work demonstrates the superior potential of photochemical reactions for the synthesis of high-performance molecular PTAs.

A Diradicaloid Small Molecular Nanotheranostic with Strong Near-Infrared Absorbance for Effective Cancer Photoacoustic Imaging and Photothermal Therapy.

Organic small molecule-based phototheranostics hold great promise for clinical translation by virtue of their distinct chemical structure, easy reproducibility, and high purity. However, reported molecular agents typically have relatively low optical absorbances, particularly over the near-infrared (NIR) region, and this limits their phototheranostic performance. Herein, we first exploit a diradicaloid molecular structure for enhancing NIR absorption to facilitate efficient photoacoustic imaging (PAI)-guided photothermal therapy (PTT). The donor-acceptor interaction in the diradicaloid molecule (DRM) leads to strong charge transfer resulting on obvious diradical characteristics, which is beneficial for NIR absorption. The DRM possesses excellent light-harvesting ability, with a mass extinction coefficient of ∼220 L g-1 cm-1, which is much higher than those (∼5-100 L g-1 cm-1) of typical organic molecules. After assembling into nanoparticles, they show good water dispersibility, good photostability, and impressive performance for PAI-guided PTT in vitro and in vivo. The impressive in vitro and in vivo performances show that developing small molecules with diradicaloid structures can be an effective approach for enhancing NIR harvesting capability for biomedical applications.

Development of a molecular K+ probe for colorimetric/fluorescent/photoacoustic detection of K.

The potassium ion (K+) plays significant roles in many biological processes. To date, great efforts have been devoted to the development of K+ sensors for colorimetric, fluorescent, and photoacoustic detection of K+ separately. However, the development of molecular K+ probes for colorimetric detection of urinary K+, monitoring K+ fluxes in living cells by fluorescence imaging, and photoacoustic imaging of K+ dynamics in deep tissues still remains an open challenge. Herein, we report the first molecular K+ probe (NK2) for colorimetric, fluorescent, and photoacoustic detection of K+. NK2 is composed of 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) as the chromophore and phenylazacrown-6-lariat ether (ACLE) as the K+ recognition unit. Predominate features of NK2 include a short synthetic procedure, high K+ selectivity, large detection range (5-200 mM), and triple-channel detection manner. NK2 shows good response to K+ with obvious color changes, fluorescence enhancements (about threefold), and photoacoustic intensity changes. The existence of other metal ions (including Na+, Mg2+, Ca2+, Fe2+) and pH changes (6.5-9.0) have no obvious influence on K+ sensing of NK2. Portable test strips stained by NK2 can be used to qualitatively detect urinary K+ by color changes for self-diagnosis of diseases induced by high levels of K+. NK2 can be utilized to monitor K+ fluxes in living cells by fluorescent imaging. We also find its excellent performance in photoacoustic imaging of different K+ concentrations in the mouse ear. NK2 is the first molecular K+ probe for colorimetric, fluorescent, and photoacoustic detection of K+ in urine, in living cells, and in the mouse ear. The development of NK2 will broaden K+ probes' design and extend their applications to different fields. Graphical abstract.

Graphene electrodes for electric poling of electro-optic polymer films.

We propose electric poling of electro-optic (EO) polymer films with graphene electrodes. The use of graphene electrodes can waive the use of buffer layers and minimize the poling voltage. To demonstrate the idea, we prepared EO polymer thin-film waveguides for poling with traditional Au/ITO electrodes and graphene electrodes, where the EO polymer is a guest-host system formed by doping 15 wt% of dipolar polyene chromophore AJLZ53 into the random copolymer P(S-co-MMA). Our experiments confirm that the use of graphene electrodes can significantly reduce the poling voltage. For a 3.8-µm-thick EO polymer film, we achieve high EO coefficients of 82 pm/V at 1541 nm and 110 pm/V at 1300 nm with a poling voltage of 420 V. In addition, the use of graphene electrodes allows more flexible waveguide designs and can potentially simplify the fabrication of devices based on EO polymer.

Silicon-Organic Hybrid (SOH) Mach-Zehnder Modulators for 100 Gbit/s on-off Keying.

Electro-optic modulators for high-speed on-off keying (OOK) are key components of short- and medium-reach interconnects in data-center networks. Small footprint, cost-efficient large-scale production, small drive voltages and ultra-low power consumption are of paramount importance for such devices. Here we demonstrate that the concept of silicon-organic hybrid (SOH) integration perfectly meets these challenges. The approach combines the unique processing advantages of large-scale silicon photonics with unrivalled electro-optic (EO) coefficients obtained by molecular engineering of organic materials. Our proof-of-concept experiments demonstrate generation and transmission of OOK signals at line rates of up to 100 Gbit/s using a 1.1 mm-long SOH Mach-Zehnder modulator (MZM) featuring a π-voltage of only 0.9 V. The experiment represents the first demonstration of 100 Gbit/s OOK on the silicon photonic platform, featuring the lowest drive voltage and energy consumption ever demonstrated for a semiconductor-based device at this data rate. We support our results by a theoretical analysis showing that the nonlinear transfer characteristic of the MZM can help to overcome bandwidth limitations of the modulator and the electric driver circuitry. We expect that high-speed, power-efficient SOH modulators may have transformative impact on short-reach networks, enabling compact transceivers with unprecedented efficiency, thus building the base of future interfaces with Tbit/s data rates.

RF photonic downconversion of vector modulated signals based on a millimeter-wave coupled electrooptic nonlinear polymer phase-modulator.

We report the RF photonic reception and downconversion of vector modulated RF signals using a millimeter-wave coupled electrooptic phase modulator with in-plane slotted patch antennas based on SEO125 nonlinear polymer. We demonstrate experimental results with QPSK, 8-PSK, 16-QAM, 32-QAM, and 64-QAM millimeter-wave signals centered at 36 GHz. After downconversion to intermediate frequencies between 0.5 GHz and 2 GHz, the vector encoded signals are demodulated using an electrical signal analyzer and found to have measured error vector magnitudes below 8%. Design, simulation, fabrication, and experimental results are presented and discussed.

Silicon-organic hybrid (SOH) modulators for intensity-modulation / direct-detection links with line rates of up to 120 Gbit/s.

High-speed interconnects in data-center and campus-area networks crucially rely on efficient and technically simple transmission techniques that use intensity modulation and direct detection (IM/DD) to bridge distances of up to a few kilometers. This requires electro-optic modulators that combine low operation voltages with large modulation bandwidth and that can be operated at high symbol rates using integrated drive circuits. Here we explore the potential of silicon-organic hybrid (SOH) Mach-Zehnder modulators (MZM) for generating high-speed IM/DD signals at line rates of up to 120 Gbit/s. Using a SiGe BiCMOS signal-conditioning chip, we demonstrate that intensity-modulated duobinary (IDB) signaling allows to efficiently use the electrical bandwidth, thereby enabling line rates of up to 100 Gbit/s at bit error ratios (BER) of 8.5 × 10-5. This is the highest data rate achieved so far using a silicon-based MZM in combination with a dedicated signal-conditioning integrated circuit (IC). We further show four-level pulse-amplitude modulation (PAM4) at lines rates of up to 120 Gbit/s (BER = 3.2 × 10-3) using a high-speed arbitrary-waveform generator and a 0.5 mm long MZM. This is the highest data rate hitherto achieved with a sub-millimeter MZM on the silicon photonic platform.

Rational Design of Dipolar Chromophore as an Efficient Dopant-Free Hole-Transporting Material for Perovskite Solar Cells.

In this paper, an electron donor-acceptor (D-A) substituted dipolar chromophore (BTPA-TCNE) is developed to serve as an efficient dopant-free hole-transporting material (HTM) for perovskite solar cells (PVSCs). BTPA-TCNE is synthesized via a simple reaction between a triphenylamine-based Michler's base and tetracyanoethylene. This chromophore possesses a zwitterionic resonance structure in the ground state, as evidenced by X-ray crystallography and transient absorption spectroscopies. Moreover, BTPA-TCNE shows an antiparallel molecular packing (i.e., centrosymmetric dimers) in its crystalline state, which cancels out its overall molecular dipole moment to facilitate charge transport. As a result, BTPA-TCNE can be employed as an effective dopant-free HTM to realize an efficient (PCE ≈ 17.0%) PVSC in the conventional n-i-p configuration, outperforming the control device with doped spiro-OMeTAD HTM.

Enhanced third harmonic generation by organic materials on high-Q plasmonic photonic crystals.

The enhanced optical nonlinearity enabled by localized plasmonic fields has been well studied for all-optical switching processing (AOSP) devices for future optical communication systems. In this work, plasmonic photonic crystals with a nonlinear polycarbonate/polymethine blend cladding layer are designed to enhance the third harmonic generation (THG) at the telecom wavelengths (~1550 nm). Due to the presence of he two-dimensional (2-D) gold nano-patch arrays with improved Q-factor and high local fields, more than 20 × of enhanced THG signals in the hybrid organic-plasmonic nanostructure are experimentally observed. The enhanced THG in the hybrid organic-plasmonic materials suggested that such extraordinary nonlinear effects can be used for AOSP devices and wavelength conversion.

Mesoporous sol-gel silica cladding for hybrid TiO2/electro-optic polymer waveguide modulators.

We report the efficient poling of an electro-optic (EO) polymer in a hybrid TiO(2)/electro-optic polymer multilayer waveguide modulator on mesoporous sol-gel silica cladding. The mesoporous sol-gel silica has nanometer-sized pores and a low refractive index of 1.24, which improves mode confinement in the 400-nm-thick EO polymer film in the modulators and prevents optical absorption from the lower Au electrode, thereby resulting in a lower half-wave voltage of the modulators. The half-wave voltage (Vπ) of the hybrid modulator fabricated on the mesoporous sol-gel silica cladding is 6.0 V for an electrode length (Le) of 5 mm at a wavelength of 1550 nm (VπLe product of 3.0 V·cm) using a low-index guest-host EO polymer (in-device EO coefficient of 75 pm/V).

Enhanced conductivity of sol-gel silica cladding for efficient poling in electro-optic polymer/TiO2 vertical slot waveguide modulators.

We report the enhanced conductivity of sol-gel silica under-cladding for efficient poling of electro-optic (EO) polymer in a hybrid EO polymer/TiO2 vertical slot waveguide modulator. The electrical volume conductivity of sol-gel silica cladding increases approximately 30 times when the calcining time of the cladding layer is critically reduced to 45 minutes, which increases the in-device EO coefficient of the 600-nm-thick EO polymer film in modulators and reduces the lower halfwave voltage (Vπ) of the modulators. The lowest driving voltage (Vπ) of the TiO2 slot waveguide modulator is 2.0 V for an electrode length (Le) of 10 mm and wavelength of 1550 nm (VπLe = 2.0 V·cm) for the low-index guest-host EO polymer SEO125. The optical propagation loss is reduced to 7 dB/cm.

Wide optical spectrum range, subvolt, compact modulator based on an electro-optic polymer refilled silicon slot photonic crystal waveguide.

We design and demonstrate a compact and low-power, band-engineered, electro-optic (EO) polymer refilled silicon slot photonic crystal waveguide (PCW) modulator. The EO polymer is engineered for large EO activity and near-infrared transparency. A PCW step coupler is used for optimum coupling to the slow-light mode of the band-engineered PCW. The half-wave switching voltage is measured to be Vπ = 0.97 ± 0.02 V over an optical spectrum range of 8 nm, corresponding to the effective in-device r(33) of 1199 pm/V and V(π) × L = 0.291 ± 0.006 V × mm in a push-pull configuration. Excluding the slow-light effect, we estimate that the EO polymer is poled with an efficiency of 89 pm/V in the slot.

Cascading Retro-Diels-Alder Cycloreversion and Sydnone-Maleimide Based Double 1,3-Dipolar Cycloaddition for Quantitative Thermal Cross-Linking of an Amorphous Polymer Solid.

A new approach to polymer cross-linking is investigated using a cascading cycloreversion of a maleimide-furan adduct and a double 1,3-dipolar cycloaddition between a sydnone and maleimide. The cross-linking proceeds quantitatively above 63 °C, despite the polymer possessing no observable glass transition temperature. The resulting polymer network possesses a high thermal stability (>300 °C) due to the irreversibility of the sydnone-maleimide cycloaddition, which releases CO2 during the cross-linking, driving the reaction. The rigid three-dimensional structure of the bis-maleimide-sydnone cycloadduct produced local free volumes in films, decreasing the dielectric constant of the material.

Trimming of high-Q-factor silicon ring resonators by electron beam bleaching.

We demonstrate a novel position-resolved resonance trimming strategy for silicon ring resonators. Ring resonators are covered with a chromophore-doped guest host polymer cladding. Illumination of the polymer cladding with high-energy electrons causes a bleaching of the chromophore molecules. Bleaching of the chromophores induces a reduction of the polymer refractive index, which can be used to trim the resonance frequency of the ring resonators. A maximum refractive index change of 0.06 and a TM polarization resonance shift of 16.4 nm have been measured. A Q factor of 20,000 before bleaching remains unaltered after the electron beam exposure process.

High-optical-quality blends of anionic polymethine salts and polycarbonate with enhanced third-order non-linearities for silicon-organic hybrid devices.

A series of anionic polymethine dyes with different aromatic counterions are prepared to improve their compatibility as guests in an amorphous polycarbonate host. When they are used as the cladding material for silicon hybrid slot waveguides, four-wave mixing wavelength conversion and two-photon absorption-based optical-power modulation are observed. Such guest-host materials may be attractive candidates for all-optical signal-processing applications.

Efficient poling of electro-optic polymers in thin films and silicon slot waveguides by detachable pyroelectric crystals.

Pyroelectric crystals are used as a conformal and detachable electric field source to efficiently pole electro-optic (E-O) polymers in both parallel-plate (transverse) and in-plane (quasi-longitudinal) configurations. Large Pockels coefficients in poled thin films and high tunability of resonance wavelength shift in hybrid polymer silicon slot waveguide ring-resonator modulators have been achieved using this method.