We report synthesis of the modified fluorene polymers tethered to the heterogeneous types of the fluorescent dyes at the cardo carbon for obtaining the dual-emissive solid materials. A series of the alternating fluorene copolymers modified with pyrene or 9,10-diphenylanthracene and BODIPY at the cardo carbon based on the red-emissive donor–acceptor structure were prepared, and their characteristics were examined. From the measurements of the optical properties, the energy transfer efficiencies were evaluated. In summary, variable energy transfer efficiencies were observed between the side chains and from the side chain to the main chain. It was indicated that the energy transfer efficiencies were strongly depended on the types of the energy donor and the detection conditions as such in the solution or film. Furthermore, it was found that the cardo fluorene units can contribute to the suppression of the energy transfer in the condensed state. Finally, the dual-emissive polymers were obtained in the film states. This is the first example, to the best of our knowledge, not only to offer systematic information on the energy transfer between the dye molecules and the polymer main-chains via the cardo structure but also to demonstrate the polymer-based optical materials with the dual-emission properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2026–2035

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.

Optically active through-space conjugated oligomers, namely, a dimer, trimer, tetramer, and cyclic trimer, consisting of a planar-chiral [2.2]paracyclophane skeleton were synthesized. In the ground state, observed similarities in the chiroptical properties of the oligomers were attributed to the equivalent orientations of two adjacent chromophores. In the excited state, the oligomers were folded into a form analogous to a one-handed helix by photoexcitation. All the compounds in dispersed solution exhibited intense circularly polarized luminescence with relatively large anisotropy factors on the order of 10⁻³.

In this manuscript, we present the hybrid materials with sulfur as an inorganic element. Initially, the network polymers with the polysulfide-bridged polyhedral oligomeric silsesquioxane were synthesized and mixed with polystyrene and poly(methyl methacrylate). The resulting polymer blends showed higher thermal degradation temperatures than that of the polymer matrix similarly as typical hybrids. Next, it was found that the sulfur-bridging networks can increase refractive indices of the polymer matrices. Moreover, it was revealed that the loss of Abbe numbers was hardly observed by blending to conventional polymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2588-2595

It is challenging to realize the near-infrared (NIR) emission with large brightness and sharp spectra from the conjugated polymers. In this study, we demonstrate the strategy for receiving strong and pure NIR emission from polymeric materials using organoboron complexes and the modification after polymerization. A series of NIR emissive conjugated polymers with boron di(iso)indomethenes (BODINs) and fluorene or bithiophene were synthesized by Suzuki–Miyaura coupling reaction. The obtained polymers exhibited high emissions in the range from deep-red to NIR region (quantum yields: ϕ_PL = 0.40–0.79, full width at half maximum height: Δλ_1/2 = 660–940 cm⁻¹, emission maxima: λ_PL = 686–714 nm). Next, the demethylation of the BODIN-based polymer with o-methoxyphenyl groups was carried out. The transformation of the polymer structure quantitatively proceeded via efficient intramolecular crosslinking through the intermediary of the boron atom. Finally, the resulting polymer showed both drastically larger red-shifted and sharper photoluminescence spectrum than that of the parent polymer with deep-red emission (ϕ_PL = 0.37, Δλ_1/2 = 460 cm⁻¹, λ_PL = 758 nm). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

We describe here the design and synthesis of the polyhedral oligomeric silsesquioxane (POSS)-based dual-functional molecular fillers for simultaneously lowering refractive indices and improving thermomechanical properties of conventional polymers. We prepared the composite films with poly(methyl methacrylate) and polystyrene containing the series of the POSS derivatives with the single functional unit for interacting with polymer chains and heptacyclopentyl substituents for creating exclusive volumes around the POSS core. From the measurements of refractive indices of polymer composites, it was revealed that all POSS fillers can lower the refractive index of the films. In addition, thermal stabilities and mechanical properties were enhanced by adding POSS fillers. The filler effect on the thermal properties can be explained by the structural features of POSS: The highly symmetrical structure of the silica cube should suppress thermal motions, resulting in the large enhancement of thermomechanical properties of polymer matrices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3583–3589

New [2.2]paracyclophane-based through-space conjugated polymers containing fluorescence quenchers such as anthraquinone and ferrocene units at the polymer termini were designed and synthesized. Their optical properties were investigated in detail. Fluorescence emission from the stacked π-electron systems was effectively quenched by the stacked π-electron systems at the polymer termini due to the energy and electron transfer through a single polymer chain; thus, the polymers acted as the molecular wire. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

A series of boron ketoiminate derivatives that exhibited clear aggregation-induced emission (AIE) characteristics (in THF: Φ_PL≤0.01; in the solid state: Φ_PL=0.30–0.76) were prepared by the reactions of 1,3-enaminoketone derivatives with boron trifluoride–diethyl etherate. The structures and optical properties were investigated by UV-visible spectroscopy, photoluminescent (PL) spectroscopy, and X-ray single-crystal measurements. These results indicate that the AIE characteristics were derived from molecular motions of the boron-chelating rings with a boronnitrogen (BN) bond. Furthermore, the optical properties were controllable by steric hindrance of the substituted groups on the nitrogen atom.

The regulation of electron transfer between a conjugated polymer and ligands orthogonally connected to the main-chain is reported. Poly(arylene-ethynylene)s containing aminoquinoline-borafluorene complexes in the main-chain are synthesized in good yields by a Sonogashira–Hagihara coupling. Single crystal X-ray analysis of a model compound has elucidated the complex's structure in which the aminoquinolate moiety and the borafluorene ring are connected directly and orthogonally. Moreover, the optical properties of the polymers are characterized by UV-vis absorption and photoluminescence spectra. Perfluorinated alkyl chain-containing polymers show strong emission, while hydrocarbon chain-containing ones exhibit only a slight emission. DFT calculation suggests that an electron transfer from the excited main-chain to the aminoquinolate ligand is suppressed because of the lowered LUMO level by introducing the electron withdrawing groups, resulting in the significant emission.

Our work on the characteristics of organoboron-containing polymers is reviewed. The electronic interaction and correlation involving organoboron complexes are responsible for the optical and electric properties of the polymers. To understand the origins of these properties and apply them to the next generation of new materials, we have gathered not only fundamental knowledge on the electronic states and behaviors of each organoboron complex in the polymers but also on the functions of the polymers in devices. In this article, we introduce our findings obtained from a series of studies on polymers involving cyclodiborazane, quinolate, diketonate, dipyrromethene, pyrazabole, and carborane complexes. In particular, there is a focus on results from recent work.

Conjugated microporous polymers (CMPs) are prepared from disubstituted and tetrasubstituted [2.2]paracyclophane monomers by a Sonogashira–Hagihara coupling. The polymers obtained exhibit a type I nitrogen gas adsorption profile and H4-like hysteresis loops, indicating that the [2.2]paracyclophane-containing CMPs possess slit-like mesopores. Their Brunauer–Emmett–Teller surface areas are estimated to be above 500 m² g⁻¹. The step and stacked structure of the [2.2]paracyclophane unit affects the morphology of the polymers because of the contribution of two-dimensional expansion of the polymer network.

The o-carborane-based π-conjugated compound, benzocarborano- [2,1-b:3,4-b′]dithiophene was synthesized. Its crystal structure revealed high coplanarity for the two thiophene rings of the 2,2′-bithiophene skeleton, which is fixed in the cisoid structure by the o-carborane unit. Theoretical calculations indicated non-aromaticity for its center C₆ ring moiety as well as decreased HOMO and LUMO levels. The o-carborane moiety provides an electron-withdrawing character to the 2,2′-bithiophene unit through an inductive effect.

[2.2]Paracyclophane-based through-space conjugated oligomers and polymers were prepared, in which poly(p-arylene–ethynylene) (PAE) units were partially π-stacked and layered, and their properties in the ground state and excited state were investigated in detail. Electronic interactions among PAE units were effective through at least ten units in the ground state. Photoexcited energy transfer occurred from the stacked PAE units to the end-capping PAE moieties. The electrical conductivity of the polymers was estimated using the flash-photolysis time-resolved microwave conductivity (FP-TRMC) method and investigated together with time-dependent density functional theory (TD-DFT) calculations, showing that intramolecular charge carrier mobility through the stacked PAE units was a few tens of percentage larger than through the twisted PAE units.

The electronic coupling via the cardo structure in polyfluorene (PFs) was investigated. The series of fluorene units alternatively having alkoxyphenyl as an electron-donating group (EDG) and/or alkyl benzoate as an electron-withdrawing group (EWG) at the cardo carbon were synthesized. From the investigation of optical properties of the polymers containing these fluorene units, it was found that the electronic states of the substituents at the cardo carbons and the PF main chains should be less influenced by the introduction of EDG and/or EWG at the cardo structure. Furthermore, these preservation effects in the cardo-PFs were observed in the film states even after the thermal treatment. We conclude that the electronic structures of the PF main chain are highly preserved from the correlations with the substituents at the cardo carbons. This is the first example, to the best of our knowledge, to survey the systematic information on the electronic structures of the cardo-PFs and offer the preservation effect of the optical properties from the introduction of EDGs and EWGs at the cardo carbon. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

The synthetic details of the P-stereogenic optically active polymer and the complexation behavior with palladium and platinum complexes are reported. The polymer consists of P-stereogenic bisphosphine units and the conjugated phenylene-ethynylene units alternately. The P-stereogenic bisphosphine moieties can coordinate to transition metals such as palladium and platinum, leading to a change in the conformation.

We have successfully synthesized optically active organoboron aminoquinolate-based coordination polymers bearing the chiral side chain derived from L-alanine, and studied their optical behavior by UV–vis and photoluminescence spectroscopies. Higher absolute quantum yields (Φ_F) of the obtained polymers, measured by integrating sphere method, were observed with electron-withdrawing substituent (Φ_F = 0.80) than with electron-donating substituent (Φ_F = 0.52). The circular dichroism (CD) study in the mixed solvents of CHCl₃ and DMF showed that the secondary structures of the obtained polymers were stabilized by hydrogen-bonding interaction in the side chain. From concentration dependence on the CD spectra, the chirality of the obtained polymers originated from the nature of one molecule. Copyright © 2009 John Wiley & Sons, Ltd.

New organoboron aminoquinolate-based polymers linked by π-conjugated bridge were prepared by Sonogashira–Hagihara coupling of organoboron aminoquinolate-based bisiodo monomers bearing biphenyl or bithiophene moiety with 1,4-diethynylbenzene derivatives. Tetracoordination states of boron atoms in the obtained polymers were confirmed by ¹¹B NMR spectroscopy, and they were also characterized by ¹H NMR and IR spectroscopies and size-exclusion chromatography. Their optical properties were studied by UV–vis absorption and photoluminescence spectroscopies. In the region above 400 nm, the polymers prepared from 1,4-diethynyl-2,5-dioctyloxybenzene showed bathochromic shifts when compared with those prepared from 1.4-diethynyl-2-perfluorooctyl-5-trifluoromethylbenzene. The polymers with biphenyl moiety showed higher absolute fluorescence quantum yields (ϕ_F = 0.28 and 0.65), whereas those with bithiophene moiety led to decreasing of the low quantum yields (ϕ_F = 0.19 and 0.00). The density-functional theory (DFT) and time-dependent–DFT calculations of model compounds corresponding to the polymers were in good agreement with the results from UV–vis properties. The calculations revealed that the electronic structure of the polymer with bithiophene moiety is different from that with biphenyl moiety, and predicted the electron transfer from the bithiophene moiety to the π-extended quinoline moiety in transition state. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3693–3701, 2010

Novel water-soluble copolymers containing 4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The copolymers with both number-average molecular weight between 5.0 × 10³ and 5.8 × 10³ and narrow molecular weight distribution (M_w/M_n < 1.19) were obtained by the copolymerization of (2-dimethylamino)ethyl methacrylate (DMAEMA) and BODIPY-based methyl methacrylate (1) with 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator in the presence of cumyl dithiobenzoate (CDB) as a chain transfer agent (CTA). The structures of the resulting copolymers were characterized by ¹H, ¹³C, and ¹¹B NMR spectroscopies, and the comonomer compositions were good consistent with the feed ratio. Characteristic optical properties of the obtained copolymers were investigated by UV-vis and PL spectroscopic methods. The copolymers composed of [DMAEMA]: [1] = 98.0:2.0 and 99.4:1.4 led to thermoresponsive polymers having phase separation temperatures at 32 °C and 40 °C, respectively, depending on the compositions of hydrophilic/hydrophobic balances. Further, the effective reversible decrease/increase of the emission intensity of the copolymers led to the reversible formation/inhibition of the H-aggregation between two BODIPY planes in the copolymers on heating and cooling across the border of LCST. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 627–634, 2010

To investigate the relationship between the chemical structures of the side chains of polyoctahedral oligomeric silsesquioxanes (POSS) fillers and the ability to decrease the refractive indices of the polymer composites, we examined the influence on the degree of polymer chain packing by the existence of the octa-substituted POSS derivatives. The polymer composites containing methyl-, ethyl-, vinyl-, isobutyl-, octyl-, octadecyl-, cyclopentyl-, and phenyl-substituted POSS in poly(methyl methacrylate) (PMMA) were prepared. The packing coefficients of the PMMA composites containing POSS derivatives were evaluated from molar refractions and refractive indices of the films with the Lorentz–Lorenz equation. We found that the ethyl group shows the lowest values of the packing coefficients and a significant effect in reducing the refractive indices of the polymer composites. Finally, in summary, it was shown that POSS molecules can intrinsically offer to reduce a packing. In addition, less entanglement and smaller interactions between polymer chains and the substitution groups are favorable to release a packing, resulting in decreases in refractive indices. Our findings described here are the first efforts to quantitatively evaluate the ability of POSS fillers to lower refractive indices at the molecular level. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

In this article, we describe the structure–property relationships between the polyoctahedral oligomeric silsesquioxane (POSS) fillers and the thermomechanical properties of the polymer composites using polystyrene, poly(methyl methacrylate), and ethylene-(vinyl acetate) copolymer. We used eight kinds of octa-substituted aliphatic and aromatic POSS as a filler, and homogeneous polymer composites were prepared with various concentrations of these POSS fillers. From a series of measurements of thermal and mechanical properties of the polymer composites, it was summarized that the longer alkyl chains and unsaturated bonds at the side chains in POSS are favorable to improve the thermal stability and the elasticity of polymer matrices. It was found that phenyl-POSS can show superior ability to improve the thermomechanical properties of conventional polymers used in this study. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5690–5697, 2009

We report the facile preparation of the conductive polymer composites containing the mixed-valence tetrathiafulvalene (TTF) nanofibers and their applications as all-organic transparent conductive materials. TTF can be used as a nanofiller for transforming conventional polymers to conductive materials. Self-assemble nanofibers of the neutral and radical cation of TTF can be formed in the polymer solutions during the film deposition, and the resulting composite films with several micron thickness can serve as the conductive material with high transparency. Several kinds of conventional polymers, such as polystyrene, poly(methyl methacrylate) (PMMA), and poly(vinylpyrrolidone), can be used as a polymer matrix of the composites. The conductivities of the PMMA film containing 35 mol % of the mixed-valence TTF and the PEDOT–PSS film showed similar values (2.8 × 10^–2 and 5.4 × 10^–1 S/cm, respectively). In contrast, the normalized transmittance of the PMMA film by 1-μm thickness greatly increased (96%/μm) when compared with that of the PEDOT–PSS film (10%/μm). In addition, the degradation of the conductivity of the nanofibers by heating and aging was effectively suppressed in the composite samples. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6441–6450, 2009

We report the synthesis of N-methylimidazolium chloride-modified iron oxide nanoparticles (MImCl-NPs) by condensation of an imidazolium cation-containing silane coupling agent (1) with the iron oxide nanoparticles which were prepared by the coprecipitation of FeCl₂ and FeCl₃ by alkaline hydrolysis. The modified iron oxide nanoparticles exhibited a superparamagnetic behavior at the room temperature. For a given weight concentration, MImCl-NPs showed a darker (T₂-weighted) image than Resovist®, which is commercially available and used for MRI imaging in practice. When mice were given a daily intravenous injection of 5% glucose aqueous solution of MImCl-NPs for two weeks, MImCl-NPs showed no significant difference in body weight and blood biochemistry of serum in all samples compared to controls. DLS measurements of the aqueous solutions of the modified iron oxide nanoparticles after the addition of NaPF₆ and NaI indicated the presence of particle aggregates. In contrast, no aggregation was observed after the addition of NaCl. A higher degree of adsorption of DNA onto MImCl-NPs was observed in comparison to that onto amino-functionalized magnetic nanoparticles (NH₂-NPs). Copyright © 2008 John Wiley & Sons, Ltd.

The development of chemically and thermally persistent blue-, and green-luminescent hybrid π-conjugated polymers consisting of poly(phenylene-ethynylene) conjugated backbone wrapped with the rigid three-dimensional polyhedral oligomeric silsesquioxane (POSS) units was successfully achieved by means of the Sonogashira-Hagihara coupling reaction. Because of the steric effect of POSS units, the luminescence stability of the conjugated backbone was significantly enhanced. Moreover, emission color was also easily tunable only by changing the ratio of POSS moieties incorporated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8112–8116, 2008

To study the bidentate coordination effect on the polycondensation of L-valinates between metal triflates as a Lewis acid and methoxy groups, we carried out the polycondensation of 2-methoxy-4-nitrophenyl L-valinate (1a) and 2-methoxyphenyl L-valinate (1b) in the presence of the various kinds of rare-earth triflates in DMF solution at room temperature. The polymerizations of 1a did not proceed without any metal triflates. In the presence of 5 mol% triflates, especially Sc(OTf)₃, the polymerization proceeded effectively. After the reaction mixture was poured into water, the product was collected, which was recognized as poly(L-valine)s by FTIR spectrum and GPC measurement. The yield of the product from the polymerization of 1a with Sc(OTf)₃ was higher than that from the polymerization of 4-nitrophenyl L-valinate (1c) with Sc(OTf)₃. This result indicates that the polymerization of 1a was promoted to introduce the methoxy group on the o-position of the phenyl ring at the ester group with the aim of the bidentate coordination effect between metal triflates and L-valinate. As a control experiment, we carried out the polycondensation of 1b in the presence of 5 mol% metal triflates; however, any polymerization did not proceeded. That reason is from the lower activity of activated L-valinate (1b). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2864–2868, 2008

Anionic poly(p-phenylene-ethynylene) (PPE) incorporated polymer hybrids were synthesized from the PPE and tetramethoxysilane together with the organic polymers such as poly(vinylpyrrolidone) via a sol–gel method. Up to 10 wt % of the anionic PPE could be dispersed homogeneously in the resulting polymer hybrid matrix. The obtained polymer hybrids exhibited controllable photoluminescence properties by the modification of the internal environment of organic–inorganic polymer hybrids by changing the organic/inorganic ratios. The photoluminescence of the anionic PPE surrounded by the polymer hybrid matrix was reinforced against the thermal irradiation. Moreover, the photoluminescence of the obtained organic–inorganic polymer hybrids was also tuned by utilizing ionic interactions between the anionic PPE and the inorganic matrix. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3749–3755, 2008

A novel hybrid-type chiral binaphthyl-based polyarylene derivative with polyhedral oligomeric silsesquioxanes (POSS) units 2a was prepared by Suzuki–Miyaura coupling polymerization from a chiral (R)-6,6′-dibromo-2,2′-diPOSS-substituted 1,1′-binaphthyl derivative 1a and p-biphenylene diboronic acid. As a reference, a binaphthyl-based polyarylene derivative without POSS unit 2b was also prepared. The obtained polymers were studied with thermogravimetric analysis, optical rotations, circular dichroism (CD), ultraviolet-visible, and photoluminescence (PL) spectra. Gel permeation chromatography measurements of 2a and 2b showed that their number-average molecular weights were 13,300 and 16,500, respectively. The thermal stability of POSS-modified polymer 2a (temperature of 10% weight loss; T₁₀ = 380 °C) was extremely high compared with that of polymer without POSS unit 2b (T₁₀ = 335 °C) due to the siliceous bulky POSS segments on the side chains. The specific optical rotation [α]_D was −66.7° (c 0.06, CHCl₃) for 2a and −62.3° (c 0.06, CHCl₃) for 2b. The CD spectra showed that these two polymers had very similar and strong Cotton effects. Film polymer 2a showed almost the same PL spectrum as that in dilute CHCl₃ solution, indicating that bulky POSS units strongly suppressed intermolecular aggregation of the π-conjugated polymer backbone. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6035–6040, 2008