Synthesis and Characterization of Gallafluorene-Containing Conjugated Polymers: Control of Emission Colors and Electronic Effects of Gallafluorene Units on π‑Conjugation System

We present synthesis and characteristics of the conjugated polymers involving organogallium complexes. A series of alternating copolymers composed of gallafluorene were prepared with diverse comonomers through various types of cross-coupling reactions such as Suzuki–Miyaura, Sonogashira–Hagihara, and Stille reactions. It was confirmed that the synthesized polymers possess solubility in common organic solvents and stability toward air and moisture. Significantly, optical properties originating from the electronic interaction between gallafluorene and various comonomers were observed. For example, vivid color emissions were demonstrated in the blue, green, yellow, orange, and red regions depending on the chemical structures of the comonomer units. In addition, it was eventually found that the benzotriazole-containing polymer showed significant optical properties originating from aggregation in the film state. From the electrochemical measurements, it was indicated that the energy levels of their frontier orbitals were varied by the comonomer units. Indeed, it is supported that the gallafluorene polymers have higher energy levels of HOMOs (highest occupied molecular orbitals) than those of the fluorene-based conjugated polymers instead of gallafluorene. Finally, it is suggested that the gallafluorene unit could work as an electron-donating group in the polymer main chain

Synthesis of Dibenzo[<i>b</i>,<i>f</i>]silepins with a Benzoquinolyl Ligand

A benzo[<i>h</i>]quinolyl ligand provided pentacoordinate character for silicon in dibenzo[<i>b,f</i>]silepins. Substituents on the silicon center determined both conformations of the dibenzosilepin and luminescence properties in relation to charge transfer

Synthesis and Optical Properties of Stable Gallafluorene Derivatives: Investigation of Their Emission via Triplet States

We designed and synthesized air- and moisture-stable gallafluorenes in which two benzene rings were bridged by the four-coordinate gallium atoms. The series of gallafluorenes were prepared by introducing electron-donating and -withdrawing groups through Suzuki–Miyaura coupling reactions. The gallafluorenes showed unique emissions via their triplet states in the presence of B­(C₆F₅)₃. These emissions were obtained via the triplet exciplex of gallafluorene and B­(C₆F₅)₃

Synthesis of Dibenzo[<i>b</i>,<i>f</i>]silepins with a Benzoquinolyl Ligand

A benzo[<i>h</i>]quinolyl ligand provided pentacoordinate character for silicon in dibenzo[<i>b,f</i>]silepins. Substituents on the silicon center determined both conformations of the dibenzosilepin and luminescence properties in relation to charge transfer

Synthesis of Dibenzo[<i>b</i>,<i>f</i>]silepins with a Benzoquinolyl Ligand

A benzo[<i>h</i>]quinolyl ligand provided pentacoordinate character for silicon in dibenzo[<i>b,f</i>]silepins. Substituents on the silicon center determined both conformations of the dibenzosilepin and luminescence properties in relation to charge transfer

Effective Light-Harvesting Antennae Based on BODIPY-Tethered Cardo Polyfluorenes via Rapid Energy Transferring and Low Concentration Quenching

Light-harvesting antennae (LHA) were demonstrated using polyfluorenes (PFs) modified with borondipyrromethene (BODIPY) dyes tethered to the cardo structures. PFs work as a light absorber and an energy donor to the BODIPY units. The series of BODIPY-tethering PFs via the cardo carbon including homocardo PFs and alternative polymers with fluorene and the cardo fluorene were synthesized, and their optical properties were investigated. Initially, highly efficient energy transferring was observed from the PF main chains to the BODIPY unit (99%). It was found that PFs can work as an efficient light absorber because of the large molar extinction coefficient and cause the rapid energy transfer through the cardo structure. Next, from the comparison with the emission efficiency of the BODIPY units in the series of the synthetic polymers, the favorable position of the BODIPY units was obtained to avoid the concentration quenching: The alternative polymer with cardo fluorene and dialkyl-substituted fluorene showed the largest emission efficiency in this study. Finally, we received the effective LHA with the 9 times larger amplification efficiency compared to that of the unimolar BODIPY unit. The results from the computer modeling suggest that the positions of the BODIPY units via the cardo structure could play a significant role in the inhibition of aggregation and electronic coupling with the BODIPY units, leading to the suppression of concentration quenching. Here is presented the feasibility of the cardo structure in fluorene as a scaffold for designing advanced optical materials

Motion control of a snake robot moving between two non-parallel planes

<p>A control method that makes the head of a snake robot follow an arbitrary trajectory on two non-parallel planes, including coexisting sloped and flat planes, is presented. We clarify an appropriate condition of contact between the robot and planes and design a controller for the part of the robot connecting the two planes that satisfies the contact condition. Assuming that the contact condition is satisfied, we derive a simplified model of the robot and design a controller for trajectory tracking of the robot’s head. The controller uses kinematic redundancy to avoid violating the limit of the joint angle and a collision between the robot and the edge of a plane. The effectiveness of the proposed method is demonstrated in experiments using an actual robot.</p

Conjugated Polymers Based on Tautomeric Units: Regulation of Main-Chain Conjugation and Expression of Aggregation Induced Emission Property via Boron-Complexation

To understand the contribution of the tautomeric units to the π-conjugation through the polymer main-chain, the characteristics of the conjugated polymers containing the ketoimine moiety were investigated. Though the ketoimine skeleton usually forms the enaminoketone structure, the electronic structure in the ketoimine units can be fixed in enolimine form by boron complexation. By employing this fixing effect, we sought to regulate the electronic structure and evaluate the change in degree of main-chain conjugation. The polymerization was executed in Suzuki–Miyaura coupling reactions with the ketoimine or the boron ketoiminate monomers. The characterization and the determination of the structures of the products were performed with NMR spectrometry. The optical and electrochemical properties were examined by UV–vis absorption spectroscopy, photoluminescence spectroscopy, and cyclic voltammetry. The degree of main-chain conjugation was evaluated from the peak shifts in the absorption and emission bands. Initially, it was observed that the conjugated system intrinsically extended even through the enaminoketone structure in which the main-chain conjugation should be inhibited. In addition, as we expected, it was indicated that the boron complexation to the ketoimine units can contribute to the extension of π-conjugation through the main-chain. Furthermore, it was found that the boron ketoiminate polymers exhibited aggregation-induced emission properties

Tunable Optical Property between Pure Red Luminescence and Dual Emission Depended on the Length of Light-Harvesting Antennae in the Dyads Containing the Cardo Structure of BODIPY and Oligofluorene

The design and synthesis of light-harvesting antenna (LHA) and alternative properties between pure red luminescence and dual emission are demonstrated. The dyads composed of size-defined oligofluorenes including trimer (<b>O3</b>), pentamer (<b>O5</b>), and heptamer (<b>O7</b>) as a light absorber and red-emissive boron dipyrromethene (BODIPY) derivative linked via the cardo carbon were prepared. As we expected, amplified emission via the LHA process in the red region was obtained (Φ > 0.78). By increasing the number of fluorene repeats from 3-mer to 7-mer, the light absorption ability increased, leading to large LHA efficiency. Especially, owing to the steric distribution of the conjugation components on the basis of the cardo carbon, electronic interaction was suppressed in the dyad. Then, intrinsic emission properties such as sharp and intense spectra can be preserved. Interestingly, it was observed that <b>O7</b> showed dual emission from both oligofluorene and BODIPY units. From the mechanistic analyses, it was revealed that energy transfer was suppressed only in <b>O7</b> (<b>O3</b>, <b>O5</b>: >0.95, <b>O7</b>: <0.70). It was implied that the effective exciton diffusion length on the oligofluorene might be from 5 to 7 fluorene units. In <b>O7</b>, the exciton could be localized in the part of the oligofluorene unit. Therefore, some percentage of the exciton could show emission in the oligofluorene unit before energy transfer

Solid-State Near-Infrared Emission of π‑Conjugated Polymers Consisting of Boron Complexes with Vertically Projected Steric Substituents

The development of solid-state near-infrared (NIR)-emissive π-conjugated polymers (CPs) has been still difficult due to lack of valid guidelines for avoiding aggregation-caused quenching. To obtain solid-state emission, we designed new strong electron acceptors by employing boron-fused azobenzene complexes with vertically projected bulky substituents at boron, which can prevent the π-surface from intermolecular interactions. Herein, we demonstrate donor–acceptor-type CPs with NIR emission properties. In summary, the CP with a bithiophene donor bearing the bulkiest substituent exhibited excellent solid-state NIR emission (λFL = 806 nm, ΦFL = 7.5%). In addition, the longest emission maximum was obtained from the CP containing cyclopentadithiophene (λFL = 923 nm, ΦFL = 0.9%). The concept for the introduction of vertically projected bulky substituents at boron opens a new research field on solid-state NIR-emissive materials