Yuichi Kajiwara

Efficient simultaneous emission from RGB-emitting organoboron dyes incorporated into organic–inorganic hybrids and preparation of white light-emitting materials

In order to investigate dye-dispersion behaviors in organic–inorganic hybrids, we incorporated RGB light-emitting organoboron dyes (1,3-diketonate BF2 complex, borondipyrromethene (BODIPY), and boron di(iso)indomethene as blue, green and red light-emitting dyes, respectively) into poly(2-hydroxyethyl methacylate) (PHEMA)–silica hybrids prepared by the microwave-assisted technique. Photoluminescence spectra of two dyes in various concentrations and Stern–Volmer plots indicate that the energy transfer efficiencies between the dyes in the hybrids were lower than that in the solution state, resulting from the suppression of concentration-quenching. Furthermore, we demonstrate the color tuning for preparing white light-emitting hybrids based on simultaneous RGB light-emission of the organoboron dyes. Finally, pure white light-emitting hybrids were obtained by the microwave-assisted in situ method.

Microwave-assisted preparation of intense luminescent BODIPY-containing hybrids with high photostability and low leachability

Organic-inorganic hybrids with high luminescence were facilely obtained by a one-pot process through the combination of sol–gel condensation and radical copolymerization. The sol–gel reaction of methyltrimethoxysilane (MeTMOS) was carried out together with radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) with methacrylate-tethering boron dipyrromethene (BODIPY) dye 1, which was prepared by the reaction of a meso-butyl-substituted BODIPY dye and potassium methacrylate, under microwave irradiation or conventional heating conditions. The obtained hybrids were characterized by UV-vis and photoluminescence spectroscopies, and differential scanning calorimetry (DSC) thermogram, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) measurements. Microwave irradiation led to a more rapid and homogeneous reaction as compared to conventional heating conditions. Therefore, the obtained hybrids by means of microwave irradiation showed higher transparency owing to inhibition of aggregation derived from π–π stacking of BODIPY units. Quantum yields (ΦF = ∼94%) of the obtained hybrids were higher than those of 1 in methanol solution. Photostability of the hybrids was improved in comparison with that of poly(HEMA-co-1) film due to shielding by silica matrices; i.e., the access of oxygen in the excited state of BODIPY units is avoided. Moreover, the elution of BODIPY dye 1 from the hybrids was significantly reduced as compared to BODIPY dye without the methacrylate group due to the covalent bond between HEMA polymer and 1.