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The significance of NIR light-absorbing and/or emitting materials is growing day by day in industrial applications as well as research fields because of intrinsic versatility of NIR light. The uniq...

Leakage of volatile organic compounds (VOCs) is one of the most severe industrial problems, because it can cause environmental pollution, global warming, fire, and explosion. Hence, the visualization of leakage is an essential technology to detect it at an early stage. Molecular crystals, fluorescence color of which can be changed by the exposure to VOCs could potentially serve as the sensing materials for realizing rapid and facile VOC detection. However, these materials usually require harsh conditions, such as heating or a vacuum, to recover their initial phases for reuse. Therefore, it remains a challenge to obtain completely reversible sensing systems without such energy-consuming recycling processes. Herein, the reversible color change of fluorescence from the crystals of a propeller-shaped boron β-diketiminate complex is reported. The complex was crystallized in distinct crystalline phases having different luminescent colors. Importantly, these phases were interconverted very rapidly (time constant

We report conjugated polymers consisting of boron formazanate in the main chains. By employing typical donor-type comonomers, such as fluorene and bithiophene, copolymers were prepared with the Mig...

Stimuli-responsive luminescent materials have received much attention as next-generation smart materials for various applications, including their use as biomedical probes, for the visualization of pollutants and sensing toxic gases. Boron-containing luminophores have been widely utilized to achieve such sensing materials because of their vacant 2pz orbital, which is responsible for their Lewis acidity, electron-accepting properties, and ability to form complexes. In addition, polymeric structures often enhance stimuli-responsivity because slight environmental changes around the molecules can dramatically affect their molecular motions, shapes and physical properties. This review describes the development of stimuli-responsive materials using various kinds of luminescent boron compounds, focusing on the mechanisms of the sensing abilities and the molecular designs.

Terphenyl-substituted borole was prepared through the nucleophilic substitution reaction with chloroborole derivative and terphenyl lithium. From recrystallization, two types of pseudo polymorphs as co-crystals with benzene and hexane were obtained. Owing to the extremely high durability of the crystalline sample in open air, not only X-ray crystallography but also optical measurements in the solid state can be executed. From structural analyses, it was proposed that strong electronic intramolecular interaction should be involved, compared to other boroles. Indeed, from the optical measurements, borole has absorption even in the near-infrared (NIR) region, suggesting that this stronger interaction should be inducible to large degree of stabilization of the electronic conjugation, followed by a significant redshift in the absorption band. Moreover, contrary to high durability in the solid state, degradation rapidly proceeds in the solution state. From the characterization of decomposition compounds, an unexpected ring-fused molecule was obtained, indicating that unique C–H bond activation at the sp3 carbon occurs. These data propose that our molecule should be versatile for designing a novel C–H activation reaction as well as obtaining advanced optoelectronic organic devices based on the unique electronic properties of borole.

Complexation of π-conjugated ligands by metal or semimetal ions leads to the enhancement of the planarity and rigidity of π-conjugated systems. Boron, especially, has played a central role in the design of luminescent main-group complexes. However, these complexes still suffer the disadvantage of aggregation-caused quenching as well as typical organic fluorophores. It has recently been reported that some types of boron complexes exhibit the aggregation-induced emission (AIE) property. Moreover, AIE behavior from complexes and organometallic compounds composed of the other group 13 elements, such as aluminum and gallium, has emerged in this decade. These observations greatly encourage us to develop advanced functional materials based on the group 13 elements. Indeed, recent research has demonstrated that these classes of materials are potentially versatile scaffolds for constructing chromic luminophores, efficiently emissive π-conjugated polymers and so on. This review mainly describes AIE-active group 13 complexes with four-coordinate structures and their application as photo-functional materials. Proposed mechanisms of the origins of AIE behavior are briefly discussed., Group 13 elements and various ligands have been getting together and paving a new way to develop advanced solid-state luminescent materials with aggregation-induced emission.

Herein, 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.

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.

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.

This paper presents the aggregation-induced emission (AIE) properties of o-carborane derivatives and proposes a potential strategy for constructing AIE-active organoboron complexes via the enhancement of freedom of intramolecular mobility. Initially, the optical properties of o-carborane derivatives with or without the fused ring structure at the C–C bond in o-carborane in which elongation should be induced by photo-excitation according to theoretical calculations were compared. Accordingly, it was shown that large mobility at the C–C bond in o-carborane should be responsible for the annihilation of emission in solution, leading to the AIE property. From this result, it was presumed that by enhancing the freedom of intramolecular mobility in conventional luminescent organoboron complexes, the deactivation of the excited state in solution and emission recovery in the aggregate can be induced. Based on this idea, we have performed several studies and introduce two representative results. Firstly, the decrease in luminescent properties of boron dipyrromethene (BODIPY) in solution by introducing a movable functional group is explained. Next, the AIE behaviors of boron ketoiminates and the potential mechanism concerning conformational changes for the deactivation of the excited state in the solution state are illustrated. It is proposed that enhancement of the freedom of mobility in the excited state of luminescent organoboron complexes could be a potential strategy for realizing AIE behaviors.

We herein describe the syntheses and characterization of extended germa[N]pericyclynes, which are macrocycles composed of germanium-butadiyne units. The obtained novel extended germa[4]-[8]pericyclynes were characterized by X-ray crystallography, UV-Vis spectroscopy, fluorescence and phosphorescence emission spectroscopy, and cyclic voltammetry, and exhibited characteristic absorptions and emissions. Density functional theory (DFT) calculations suggested smaller HOMO-LUMO gap energy compared to that of general germapericyclynes.

Aluminum hydrides are versatile compounds utilized as reducing agents, precursors of aluminum complexes, and as catalysts for polymerization reactions. However, their photophysical properties have been overlooked, although several luminescent aluminum complexes have been utilized conventionally for emitting layers in modern light-emitting devices. Herein, we report the synthesis and photophysical properties of a luminescent &beta, diketiminate dihydride complex through the reaction between lithium aluminum hydride and the corresponding ligand. The obtained compound exhibits crystallization-induced emission (CIE) properties at room temperature and long-lifetime phosphorescence at 80 K. Our experimental and theoretical investigations suggest that low-energy molecular vibration could play an important role in the realization of the CIE property.

Three structurally disordered terpolymer derivatives of PffBT4T-2OD (PCE11), prepared by replacing a varied amount of bithiophene linkers with single thiophenes, were found to exhibit reduced aggregation in solution with increasing thiophene content, while important redox and optoelectronic properties remained similar to those of PffBT4T-2OD. Solar cells based on random terpolymer-PC71BM blends exhibited average power conversion efficiencies of over 9.5% when processed with preheated substrates, with fill factors above 70%, exceeding those from PffBT4T-2OD. Thanks to increased solubility, random terpolymer devices were able to be fabricated on room-temperature substrates, reaching virtually identical performance among all three polymers despite remarkable thicknesses of ∼400 nm. Thus, we show that the random terpolymer approach is successful in improving processability while maintaining device performance.

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.

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.

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.

Multi-colored solar cells sensitized with organic dyes were developed by optimizing electrolytes and counter electrodes to enhance the transparence of the both by reducing the concentration of iodine dissolved in the imidazolium-based electrolytes and by employing a platinum layer of a 0.5 nm thickness. The solar cells were assembled by using nano-crystalline TiO2 electrodes adsorbing sensitizing dyes, an electrolyte consisting of a mixture of iodine and 1-butyl-3-methylimidazolium iodide in a 0.2:10 molar ratio and the counter platinum electrode to give cells bearing red, purple, blue, green and black colors. The multi-colored solar cells were connected in series to exhibit a 2.1% conversion efficiency under AM 1.5 (1 sun, 100 mW cm−2) irradiation with a total semiconductor area of 25 cm2.

We have developed an efficient and novel polyene-dye-sensitized nanocrystalline TiO2 solar cells producing a 6.8% solar energy-to-electricity conversion efficiency (eta) under AM 1.5 irradiation (100 mW cm(-2)): short-circuit current density (Jsc), 12.9 mA cm(-2), open-circuit photovoltage (Voc), 0.71 V, fill factor (ff), 0.74.