The Department of Applied Chemistry deals with a wide variety of topics related to chemistry; from the development and characterization of new materials to the development of the technology to effectively produce and distribute them to our community.
The school was opened in 2010, when Akira Suzuki (Professor Emeritus, Hokkaido University) won the Nobel Prize in Chemistry fusing chemistry in science (which plays a role in fundamental chemistry education/research) and chemistry in engineering (which focuses on practical learning).
The glass-transition properties and temperature-sensitive luminescence of lanthanide (Ln(III)) coordination compounds are reported. The glass formability was systematically provided by incorporation of bent-angled phosphine oxide (2,5-bis(diphenylphosphorylethynyl)thiophene: dpet, 2,7-bis(diphenylphosphorylethynyl)naphthalene: dpen, 1,3-bis(diphenylphosphorylethynyl)benzene: m-dpeb) ligands with thienyl, naphthyl, phenyl cores, and ethynyl groups. The glass-transition points were clearly identified for all Ln(III) coordination compounds (Tg = 65–87 °C). The Tb(III)/Eu(III) mixed coordination glass [Tb,Eu(hfa)3(m-dpeb)]3 (hfa: hexafluoroacetylacetonate) also showed green, yellow, orange, and red photoluminescence depending on temperature.
Seven‐coordinate TbIII complexes with strong luminescence and thermosensing properties are reported. Mononuclear [Tb(tmh)3(PEB)] [tmh: 2,2,6,6‐tetramethyl‐3,5‐heptanedione, PEB: (diphenylphosphoryl)ethynyl]benzene and dinuclear [Tb2(tmh)6(m‐BPEB)] [m‐BPEB: 1,3‐bis(diphenylphosphoryl)ethynyl]benzene were characterized by single‐crystal X‐ray analysis. The quantum yields of [Tb(tmh)3(PEB)] and [Tb2(tmh)6(m‐BPEB)] were estimated to be 71 and 39 %, respectively. Thermosensing properties are evaluated by temperature‐dependent emission lifetime measurements (Arrhenius analysis), which are affected by the presence of ligand‐to‐ligand charge transfer (LLCT) bands. The LLCT bands are confirmed by DFT calculations.
Novel Eu(III) coordination polymers with furan-based bridging ligands [Eu(hfa)3(Cy)]n and [Eu(hfa)3(Tol)]n (hfa: hexafluoroacetylacetonato, Cy: 2,5-bis(dicyclohexylphosphoryl)furan), Tol: 2,5-bis(di-p-tolylphosphoryl)furan) are reported. The rigidity of assembly steric structures was controlled by intermolecular interactions through the side groups in bridging ligands. They exhibited one of the best performances (thermal stability above 320 °C and external photoluminescence quantum yields of up to 71%) among reported lanthanide(III) compounds. The triboluminescence activity was demonstrated to be dependent on the mechanical stability of the coordination polymers, which was proportional to the number of hydrogen atoms in the side groups. The second example of a large TL/PL spectral difference in [Tb,Eu(hfa)3(Tol)]n also revealed discrete photophysical processes under the conditions of grinding and UV irradiation.
The steric structures of luminescent compounds play a key role in controlling the thermal and optical properties. In order to improve the thermal properties of a strong luminescent Eu(III) coordination polymer [Eu(hfa)3(dpedot)]n (hfa: hexafluoroacetylacetonate, dpedot: 2,5-bis(diphenylphosphoryl)-3,4-ethylenedioxythiophene) in our previous study, a dithiane hexyl ring was introduced instead of a dioxane one. The prepared [Eu(hfa)3(dpedtt)]n (dpedtt: 2,5-bis(diphenylphosphoryl)-3,4-ethylenedithiothiophene) exhibited thermal stability by suppressing side group decomposition. The dpedtt ligand showed a smaller dipole moment than that of dpedot, and [Eu(hfa)3(dpedtt)]n formed less twisted and densely packed polymer chains, resulting in excellent photophysical properties (quantum yield > 60%).
According to the crystal field theory, the forbidden selection rules in lanthanide’s 4f-4f transition can be relaxed by highly asymmetric structures around the lanthanide ion. Their radiative rates can be increased, facilitating for strong luminescent complex. Geometries of seven-coordination structures are more asymmetric than those of most common eight-coordination ones. In this review, luminescent seven-coordinated lanthanide complexes were introduced. Their photophysical properties are dependent on antenna molecules, ancillary ligands and surrounding media. Photophysical properties and applications using seven-coordinate lanthanide complexes are also presented in this review.