Shunichiro Ito

Modulation of sensitivity to mechanical stimulus in mechanofluorochromic properties by altering substituent positions in solid-state emissive diiodo boron diiminates

This manuscript describes modulation of the sensitivity to mechanical forces in diiodo boron diiminates by altering the substituent position of iodine groups. A series of modified complexes were prepared, and their solid-state luminescence properties based on aggregation and crystallization-induced emission mechanisms were observed. By adding mechanical forces to the crystalline samples of each complex, changes in the optical properties were monitored. Interestingly, peak shift degree of the emission bands was varied. From X-ray crystallographic analyses, it was shown that molecular distributions in the crystal packing significantly depended on the positions of the iodine groups in the complex. In particular, it was found that by increasing the dihedral angles between the phenyl substituents and the boron-containing six-membered ring, a larger peak shift width was obtained. Finally, the most planar conformation of the complexes was detected from the complex insensitive to mechanical forces. It was suggested that intramolecular electronic conjugation in the initial crystalline state could be responsible for the degree of peak shift. This is the first example, to the best of our knowledge, to offer regulation of sensitivity to mechanical forces in a series of structural isomers with the same chemical component.

Size-discrimination of volatile organic compounds utilizing gallium diiminate by luminescent chromism of crystallization-induced emission via encapsulation-triggered crystal–crystal transition

This manuscript describes the role of multi-functional gallium diiminate in photochemistry, crystal structural transition and molecular recognition. Discrimination of volatile organic compounds (VOCs) is a key technology to develop chemical sensors and probes such as for the detection of hazardous chemicals as well as for the assessment of air pollution. So far, there are several optical materials which can selectively capture some kinds of VOCs and present the alteration of optical properties. However, it is still rare to distinguish for only the size of VOCs by luminescent chromism regardless of chemical components of VOCs or functional groups in VOCs. This manuscript demonstrates that the size-dependent inclusion of the fumed VOCs into the solid-state emissive crystals of gallium diiminate can occur with the luminescent chromism of its crystallization-induced emission (CIE). In particular, it was shown that the degree of luminescent chromism was critically dependent not on the chemical components of the captured VOCs but on their radius of gyration (rg). Finally, it was also demonstrated that from the changes in the thermal and physical properties monitored through powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and diffuse reflectance profiles, the precise discrimination of the molecular sizes of VOCs by 0.1 A was accomplished. From the structural analyses before and after fuming VOCs to the crystalline samples of gallium diiminate, it was revealed that the crystal–crystal structural transition was induced.

Control of aggregation-induced emission versus fluorescence aggregation-caused quenching by bond existence at a single site in boron pyridinoiminate complexes

This manuscript reports the control of the luminescence properties of organoboron complexes between fluorescence aggregation-caused quenching (ACQ) and aggregation-induced emission (AIE) with or without a chemical bond at a single site in the pyridinoiminate skeleton. Novel boron complexes with (FBPI) and without (BPI) the fused structure in the ligand moiety were designed and synthesized. From the optical measurements, it was demonstrated that their solution- and solid-state emission behaviors oppositely varied with the presence of the fused structures. FBPI showed critical ACQ in a poor solvent. In contrast, BPI presented AIE behaviors. Additionally, from further evaluation of the solid-state emissive properties, it was shown that both boron complexes had crystallization-induced emission enhancement (CIEE) properties. Finally, it was demonstrated that reversible regulation of the emission intensity by external stimuli such as heating and solvent vapor fuming was accomplished with BPI based on the CIEE properties.

Preservation of main-chain conjugation through BODIPY-containing alternating polymers from electronic interactions with side-chain substituents by cardo boron structures

This manuscript describes the synthesis and electronic structures of the modified boron dipyrromethene derivatives containing cardo boron. By using organometallic reagents, the replacement of fluorine groups to aryl substituents with electron-donating groups and/or electron-withdrawing groups was accomplished, resulting in the formation of cardo boron. From the theoretical calculations and optical measurements, electronic structures in the main-chain conjugation were evaluated. In summary, it was clearly shown that cardo boron can efficiently isolate the main-chain conjugation from the electronic interaction with the side chains since the optical properties were highly preserved from the introduction of the side-chain substituents. Our findings should be fundamentally significant for the application of cardo boron-containing conjugated polymers as a scaffold to construct a multi-functional unit by the assembly of functional units.

Synthesis of Aggregation-Induced Emission-Active Conjugated Polymers Composed of Group 13 Diiminate Complexes with Tunable Energy Levels via Alteration of Central Element

Conjugated polymers containing boron and gallium diiminate complexes were prepared with various electron-donating comonomers via pre- and post-complexation methods, respectively. From a comparison of emission quantum yields between solution and film states, it was seen that all polymers containing group 13 elements possessed an aggregation-induced emission property. Additionally, the frontier orbital energies and the optical and electrochemical properties of the polymers can be tuned by altering a central element at the complex moieties as well as by changing a comonomer unit. In particular, it was demonstrated that the gallium atom can contribute to stabilizing the energy levels of the lowest unoccupied molecular orbitals, resulting in narrow band gaps of the conjugated polymers. This study presents the potential of gallium not only for preparing solid-state emissive conjugated polymers but also for fabricating low-band gap materials by employing the conjugated ligand.

Synthesis, properties and structure of borafluorene-based conjugated polymers with kinetically and thermodynamically stabilized tetracoordinated boron atoms

AbstractHerein, borafluorene-conjugated polymers with a dibromoborafluorene monomer and various boronic acid ester comonomers are reported. By employing the Suzuki−Miyaura cross-coupling reaction, a series of copolymers was prepared with the boron atoms in tetracoordinated states. Based on comparison to the optical properties of gallafluorene copolymers, higher luminescence quantum yields were obtained from the synthesized borafluorene copolymers due to the weak spin-orbit interaction of boron compared to that of gallium. Additionally, the results from the electrochemical measurements indicated that the electron-withdrawing property of the boron atoms led to stabilization of the lowest unoccupied molecular orbitals (LUMOs) of the borafluorene copolymers. In the X-ray diffraction profiles, significant peaks originating from π−π stacking and assembly of the side chains were observed. The borafluorene copolymers were more crystalline than the gallafluorene polymers.Synthesis and properties of borafluorene-containing conjugated polymers with various comonomers are presented. From the comparison with the gallafluorene copolymers, higher luminescent quantum yields were obtained from the borafluorene copolymers. Additionally, from the electrochemical measurements, it was shown that the electron-withdrawing property of the boron atoms led to the stabilization of LUMOs of the borafluorene copolymers. In the X-ray diffraction profiles, the significant peaks originated from π−π stacking and assembly of the side chains were observed. The borafluorene copolymers were more crystalline materials relative to the gallafluorene polymers.

Arene-Inserted Extended Germa[n]pericyclynes: Synthesis, Structure, and Phosphorescence Properties

This report describes the synthesis and characterization of arene-inserted extended (ArEx) germa[n]pericyclynes composed of germanium and 1,4-diethynylbenzene units. These novel cyclic germanium-π unit materials were synthesized with diethynylbenzene and germanium dichloride. X-ray crystallographic analysis revealed their structures, and the planar conformation of ArEx germa[4]pericyclyne along with the regular aromatic rings. UV/Vis absorption spectra and fluorescence emission spectra showed considerably unique and highly improved character compared to previously reported germa[n]pericyclynes. Even in the absence of transition metal components, phosphorescence emissions were observed, and the emission lifetimes were dramatically improved. ArEx germa[n]pericyclynes showed high photoluminescence quantum yields, whereas low photoluminescence quantum yields were observed for acyclic compounds. Density functional theory calculations show delocalized orbitals between skipped alkyne units through a germanium tether, and an increase in the HOMO energy level, leading to a small HOMO-LUMO energy gap.

Luminescent color tuning with polymer films composed of boron diiminate conjugated copolymers by changing the connection points to comonomers

A series of alternating copolymers composed of boron diiminate were synthesized with variable connection points to the comonomer units. All polymers had aggregation-induced emission (AIE) properties, and their films presented diverse colors from green to orange depending on the type of comonomer such as fluorene and bithiophene and the connection points. From mechanistic studies, it was found that the charge transfer character was varied in the emission properties of the polymers. Theoretical investigation proposed that boron diiminate worked as a strong electron-acceptor in the excited state when the comonomers were connected to one or both the phenyl groups on the nitrogen atoms. In contrast, when the comonomers were linked at the phenyl groups on the carbon atoms in the boron-containing six-membered ring, a weak electron-donating property was induced. This is the first example, to the best of our knowledge, to tune the luminescence properties with AIE-active conjugated polymers without changing the chemical components.