The review reports the recent progress in organic second-order and third-order nonlinear optical materials in the Jen group.

Textile-based wearable devices have attracted increasing attention because of their softness, breathability, and biocompatibility, which makes them durable and wearable for long-term application. To date, the fabrication of multifunctional wearable electronic textiles (E-textiles) that integrate sensing and heating properties via an energy-saving method remains a great challenge. Herein, we have proposed a multifunctional integration strategy using integrated nanowire-coated fabrics that can deliver pressure sensing capabilities simultaneously with thermal insulation, Joule heating, and particulate matter (PM) filter features. The collective effect of the fiber/yarn/fabric multi-scale contacts produces a highly sensitive multifunctional E-textile, with a sensitivity of approximately 3.24 × 10⁵ kPa⁻¹ at 0–10 kPa and 2.16 × 10⁴ kPa⁻¹ at 10–100 kPa, respectively. Each layer contained a conductive network of metallic nanowires (NWs) that could reflect the infrared radiation (IR) emitted by the human body and synergistically enhance the thermal insulation property of the multifunctional E-textile, thus enabling a 5 °C decrease in the setpoint as compared to the normal cotton textile. In addition to passively insulating heat loss, the E-textile can also function as a wearable heater, inducing fast thermal response and uniform electroheating. Furthermore, it can act as a high-efficiency air filter for high-temperature PM2.5 particle removal. The outstanding integrated property is expected to be applicable in the fields of smart clothes, human monitoring and healthcare, air filtration, and lightweight body armor in extreme climate conditions.

In organic electro-optic (EO) materials, strong dipole–dipole interactions hinder the highly efficient poling of nonlinear optical chromophores. Supramolecular self-assembly through π–π stacking of fluoroaromatics was proved to be one of the most effective strategies to simultaneously achieve high chromophore loading density and highly efficient poling. Herein, we demonstrated a new strategy of supramolecular homodimerization to self-assemble EO dendritic films, in which two dendritic units with semifluorinated dipolar 1,2,3-trifluorobenzene (TFB) moieties were attached to the donor end and the π-bridge centre of push–pull tetraene chromophores. In these new dendrimers, the use of monolithic and semifluorinated TFB rings to replace the heterodimers of phenyl and pentafluorophenyl moieties has greatly simplified the synthesis of dendrimers and their intermixing, and can further potentially enable more efficient and rapid intermixing of interacting moieties in the solid states than those in binary and ternary systems. Photophysical property analysis and DFT calculations were carried out to understand the macroscopic supramolecular self-assembly and microscopic polarizability of new TFB-based EO dendrimers. The poled films of these self-assembled dendritic EO films exhibited very large EO coefficients up to 248 pm V⁻¹ at a wavelength of 1310 nm and excellent temporal stability at room temperature with a very minimal change of ∼5% for over 1000 hours. Our study therefore illustrates that homodimer stacking of TFB rings through dipole–dipole coupling provides stabilization energy similar to that of quadrupolar interaction of phenyl and pentafluorophenyl heterodimeric pairs. Due to the highly efficient poling and excellent temporal EO stability, TFB self-assembled EO dendrimers show great potential for application in photonic devices.

It is essential to bias a thin-film lithium-niobate Mach-Zehnder electro-optic (EO) modulator at the desired operation condition to ensure optimal performance of the modulator. While thermo-optic (TO) control can solve the problem of bias drift, it consumes significant electric power. In this paper, we propose a technique to largely reduce bias power consumption by combining passive bias and TO bias. In our design, waveguide sections with different widths are introduced in the two arms of the MZ modulator to produce a desired phase difference of π/2 rad (the desired operation condition), and local heating with electrode heaters placed on the waveguides is employed to provide compensation for any phase drift caused by fabrication errors and other effects. As the TO control only serves to compensate for small errors, the electric power required is low and the response is fast. To demonstrate our technique experimentally, we fabricate several modulators of the same design on the same chip. Our experimental modulators can operate up to ∼40 GHz with a half-wave voltage of ∼2.0 V over a wide optical bandwidth, and the performances are insensitive to ambient temperature variations. The TO bias powers required range from 1 mW to 15 mW, and the thermal rise and fall times are 47 µs and 14 µs, respectively. Our technique can facilitate the development of practical high-speed EO modulators on the lithium-niobate-on-insulator platform.

Organic conjugated dyes have received extensive attention due to their broad applications in nonlinear optics and light-emitting and fluorescent sensors. Herein, we report the two-step synthesis of donor–acceptor dyes with triene-conjugated bridges. Via Vilsmeier formylation and Knoevenagel condensation, the dyes 1–4 with respectively varied electron-withdrawing moieties were successfully synthesized with high yields in short duration times. Photophysical properties showed gradually enhanced intramolecular charge-transfer (ICT) strength from dye 1 to dye 4 and diverse absorption and fluorescence properties. This structure–property tuning ensured their different applications in optofluidic lasers and nonlinear optics. Moreover, an optofluidic laser obtained using dye 1 in toluene as the gain material was demonstrated. Narrow linewidth (1.6 nm) of the optofluidic laser (peak wavelength: 610 nm) with a threshold of 94.2 μJ mm⁻² was obtained. In electro-optic (EO) activities, four dyes in guest–host EO films showed the step-up EO coefficients from dye 1 (3 pm V⁻¹) to dye 4 (76 pm V⁻¹). This trend was in accordance with the results of ICT energy gap and DFT calculations, and it showed the effective tuning of structure–property relationship for electro-optics. The facile synthesis of NLO dyes, fine-tuning of their intramolecular charge-transfer, as well as the experimental demonstration in nonlinear optics and optofluidic lasers indicated their significant applications in organic photonic devices.