Amane Hirose

Functionalization of boron diiminates with unique optical properties: multicolor tuning of crystallization-induced emission and introduction into the main chain of conjugated polymers.

In this article, we report the unique optical characteristics of boron diiminates in the solid states. We synthesized the boron diiminates exhibiting aggregation-induced emission (AIE). From the series of optical measurements, it was revealed that the optical properties in the solid state should be originated from the suppression of the molecular motions of the boron diiminate units. The emission colors were modulated by the substitution effects (λ(PL,crystal) = 448-602 nm, λ(PL,amorphous) = 478-645 nm). Strong phosphorescence was observed from some boron diiminates deriving from the effects of two imine groups. Notably, we found some of boron diiminates showed crystallization-induced emission (CIE) properties derived from the packing differences from crystalline to amorphous states. The 15-fold emission enhancement was observed by the crystallization (Φ(PL,crystal) = 0.59, Φ(PL,amorphous) = 0.04). Next, we conjugated boron diiminates with fluorene. The synthesized polymers showed good solubility in the common solvents, film formability, and thermal stability. In addition, because of the expansion of main-chain conjugation, the peak shifts to longer wavelength regions were observed in the absorption/emission spectra of the polymers comparing to those of the corresponding boron diiminate monomers (λ(abs) = 374-407 nm, λ(PL) = 509-628 nm). Furthermore, the absorption and the emission intensities were enhanced via the light-harvesting effect by the conjugation with fluorene. Finally, we also demonstrated the dynamic reversible alterations of the optical properties of the polymer thin films by exposing to acidic or basic vapors.

Boron Diiminate with Aggregation‐Induced Emission and Crystallization‐Induced Emission‐Enhancement Characteristics

Organoboron complexes having aggregation- and crystalization-induced emission properties are presented. The series of boron diiminates were synthesized and the emission behaviors of the synthesized compounds were investigated. Finally, it was found that significant enhancement of the emission depended on the crystallinity in the solid states.

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.

Film-type chemosensors based on boron diiminate polymers having oxidation-induced emission properties

We present here the film-type chemosensors based on stimuli-responsive emissive polymers. The turn-on fluorescent conjugated polymers in the film state were designed by employing boron diiminates having aggregation-induced emission (AIE) properties to obtain strong emission from the solid state. We prepared the films with AIE-active copolymers composed of fluorenes and sulfide-substituted boron diiminates and evaluated the changes in their optical properties by oxidation. By soaking the film samples of the polymer in a H2O2 solution, a significant increase of the emission intensity was observed by oxidation. The quantum yields increased up to 3 times by oxidation at the sulfide groups. This would be attributed to the facilitating charge transfer (CT)-emissive fluorescence between the fluorene units and the boron diiminates having an enhanced electron-withdrawing ability by replacing the sulfide with the sulfoxide groups. These materials should be a suitable platform as bioprobes for longitudinal monitoring of bio-related reactions.

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.

Liquid scintillators with near infrared emission based on organoboron conjugated polymers

The organic liquid scintillators based on the emissive polymers are reported. A series of conjugated polymers containing organoboron complexes which show the luminescence in the near infrared (NIR) region were synthesized. The polymers showed good solubility in common organic solvents. From the comparison of the luminescent properties of the synthesized polymers between optical and radiation excitation, similar emission bands were detected. In addition, less significant degradation was observed. These data propose that the organoboron conjugated polymers are attractive platforms to work as an organic liquid scintillator with the emission in the NIR region.

Synthesis and color tuning of boron diiminate conjugated polymers with aggregation-induced scintillation properties

We report film-type scintillators based on conjugated polymers with aggregation-induced emission (AIE) properties and the modulation of their scintillation abilities by chemical modification. Alternating copolymers containing a series of boron diiminates with various substituents and comonomers were synthesized via the palladium-catalyzed cross-coupling reaction. The synthesized polymers showed AIE properties. In addition, the corresponding emission colors to photoluminescence were also obtained with X-ray excitation. These data suggest that the AIE-active polymers should be a promising platform for developing a function-tunable plastic scintillator.

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 of a Platinum Diketonate-Containing Polymer Showing Oxygen-Resistant Phosphorescence

The synthesis of a platinum diketonate-based alternating copolymer containing a fluorene unit and its oxygen-resistant phosphorescence are reported. The polymerization is executed via palladium-catalyzed Suzuki-Miyaura coupling reaction. The synthesized polymer shows good solubility in common organic solvents and processability to form homogeneous films. By optical measurements it is found that the synthesized polymer shows phosphorescence from a triplet π-π* ligand-centered transition, and interestingly, the emission is hardly influenced by oxygen. Phosphorescence is observed from both solution and film samples under aerobic conditions. The new idea of obtaining emissive materials based on conjugated polymers showing oxygen-resistant phosphorescence is presented here.