Self-Assembled π-Conjugated Organic/Polymeric Microresonators and Microlasers

Optical microresonators are minute dielectric objects that are utilized as essential components in micrometer-scale light and laser sources, optical integrated circuits, micro-displays, chemo- and biosensors, and so forth. Particularly, microresonators made from organic and polymeric materials find unique applications owing to structural flexibility, color tunability, and functionality with a simple fabrication process, low cost and low energy consumption. In this Account, we highlight our recent progress on organic/polymeric microresonators made through precisely controlled self-assembly. The microstructures display novel optical functions such as circularly polarized luminescence emission, lasing, light energy harvest, optical gate operations, optical memories and authentications, and optical sensing for environmental changes and mechanical forces. Our methodology for the precise design and control of organic and polymeric microstructures will bridge between nanometer-scale supramolecular chemistry and bulk materials and will pave the way toward flexible optical and laser applications.</p

A fluorescent microporous crystalline dendrimer discriminates vapour molecules

A self-assembled crystalline microporous dendrimer framework (MDF) exhibits novel turn-on and ratiometric fluorescence upon exposure to solvent vapours. The donor–acceptor character, combined with the large surface area (>650 m2 g−1), allows the MDF to discriminate vapours of volatile solvents with turn-on and colour change of photoluminescence

FRET-mediated near infrared whispering gallery modes: studies on the relevance of intracavity energy transfer with Q-factor

Near infrared (NIR) optical microsphere resonators are prepared by coassembly of energy-donating and accepting conjugated polymers. In the microspheres, fluorescence resonance energy transfer occurs, leading to sharp and periodic photoluminescence from whispering gallery modes in the NIR region with Q-factors as high as 600

Controlling the Dielectric Behavior of Organic Electronic Devices

In this thesis, the dielectric behavior including dielectric constants and dielectric characteristics of poly-(p-phenyleneethynylene)s (PPEs) and their influence on organic electronic devices are investigated. In the first part, a method to create gels that compose of PPE and an ionic liquid was invented and named π-ion gels. π-ion gels exhibit a high dielectric constant so that excellent performances are displayed when π-ion gels are applied to the light-emitting electrochemical cells (LECs). The turn-on time, the brightness, the current density of LECs based on π-ion gels are improved by 10 times (0.7~2 s), four times, and 10 times (~20 A/cm2) in comparison to LECs fabricated by a drop- casting method, respectively. Furthermore, π-ion gels are applied to a new type of transistors, π- ion gel transistors (PIGTs). PIGTs display the on/off ratio of ~105, the hole carrier mobility of (0.4 cm2/V s), and the response time of ~20 μs, respectively. Especially, the response time of 20 μs is the fastest among electrochemical based transistors. In the second part, a novel concept for the control of dielectric properties was developed. dipolar units of o-difluorobenzene were incorporated in both poly-(p-phenyleneethynylene)s (PPEs) and liquid-crystalline oligo-(p-phenyleneethynylene)s (PEs). When o-difluorobenzene is introduced in PPEs, ferroelectric behavior is observed as the first example of ferroelectric conjugated polymer based on molecular rotations. Furthermore, a liquid-crystalline PE forms a dipole-aligned crystal via a dual control of the electric field and the temperature (called 2D control). In both cases, the compounds are applied to metal-insulator-metal (MIM) diodes, exhibiting anisotropic currents. Overall, the approaches to control dielectric constants and dielectric characteristics are beneficial for organic electronic devices. The concept is novel and feasible to apply to other materials

Ultrafast Dynamics of Solute Molecules Probed by Resonant Optical Kerr Effect Spectroscopy

Ultrafast molecular dynamics in fluids is of great importance in many biological and chemical systems. Although such dynamics in bulk liquids has been explored by various methods, experimental tools that unveil the dynamics of solvated solutes are limited. In this work, we have developed resonant optical Kerr effect spectroscopy (ROKE), which is an analogue of optical Kerr effect spectroscopy that measures the reorientational relaxation of a dilute solute in solution. By adjusting the pump and probe wavelengths at the resonant absorption band of a solute, the time response of the solute was distinguished easily from the negligible signal of the solvent. The heterodyne detection of ROKE enables the determination of reorientational relaxation time constants with an accuracy of 2.6%. The signal-to-noise ratio was high enough (average ∼26.7) to obtain an adequate signal from even a 10 μM solution. Thus, ROKE is a powerful tool to study solute dynamics with high sensitivity in a broad range of applications

Fast Response Organic Supramolecular Transistors Utilizing In-situ π-ion Gels

Despite their remarkable charge carrier mobility when forming well-ordered fibers, supramolecular transistors often suffer from poor processability that hinders device integration, resulting in disappointing transconductance and output currents. Here, a new class of supramolecular transistors, π-ion gel transistors (PIGTs), is presented. An in situ π-ion gel, which is an unprecedented composite of semiconducting nanofibers and an enclosed ionic liquid, is directly employed as an active material and internal capacitor. In comparison to other superamolecular transistors, PIGT displays a high transconductance (133 µS) and output current (139 µA at -6 V), while retaining a high charge-carrier mobility (0.16 cm2 V-1 s-1) and on/off ratio (3.7*104). Importantly, the unique device configuration and the high ionic conductivity associated with the distinct nanosegregation enable the fastest response among accumulation-mode electrochemical-based transistors (< 20 µs). Considering the advantages of the absence of dielectric layers and the facile fabrication process, PIGT has great potential to be utilized in printed flexible devices. The device platform is widely applicable to various supramolecular assemblies, shedding light on the interdisciplinary research of supramolecular chemistry and organic electronics.</p

Poly(aryleneethynylene) Tongue That Identifies Nonsteroidal Anti-Inflammatory Drugs in Water: A Test Case for Combating Counterfeit Drugs

We report a sensor array composed of a highly fluorescent positively charged poly­(<i>para</i>-phenyleneethynylene) <b>P1</b> and its complex <b>C</b> with a negatively charged pyridine-containing poly­(<i>para</i>-aryleneethynylene) <b>P2</b> (quencher) at pH 10 and pH 13; a sensor field composed of four elements, <b>P1</b> (pH 10), <b>P1</b> (pH 13), <b>C</b> (pH 10), and <b>C</b> (pH 13), results. The elements of this small sensor field experience either fluorescence turn on or fluorescence quenching upon exposure toward nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin, ibuprofen, diclofenac, or naproxen. The combined responses of the sensor field are analyzed by linear discriminant analysis (LDA). All of the NSAIDs were identified and discriminated, and the sensing mechanism, hydrophobic versus electrostatic, was discussed

Solid-State Gels of Poly(<i>p</i>‑phenyleneethynylene)s by Solvent Exchange

Solutions of dialkoxy- and dialkyl-poly­(<i>p</i>-phenyleneethynylene)­s (PPE) form well-defined solid state gels by diffusion of a nonsolvent (SOG), even if the concentration of the PPEs is only 2.5 mg/mL. The residual solvent in the SOG gel does not contain any dissolved PPE according to fluorescence and emissive lifetime measurements. The solvent inside of the gels is confirmed to be more than 90% of the polar solvent, which gives temperature stability to the gel and makes it available for infiltration of analytes, etc. This is in strong contrast to “classic” gels that form by thermal gelation; these still contain dissolved PPE chains. As a result, an ionic-liquid-filled PPE gel could be formed successfully by solvent exchange