Yuichi Hirai

Luminescent Europium(III) Coordination Zippers Linked with Thiophene-Based Bridges

Novel Eu(III) coordination polymers [Eu(hfa)3 (dpt)]n (dpt: 2,5-bis(diphenylphosphoryl)thiophene) and [Eu(hfa)3 (dpedot)]n (dpedot: 2,5-bis(diphenylphosphoryl)ethylenedioxythiophene) with hydrogen-bonded zipper structures are reported. The coordination polymers are composed of Eu(III) ions, hexafluoroacetylacetonato ligands, and thiophene-based phosphine oxide bridges. The zig-zag orientation of single polymer chains induced the formation of densely packed coordination structures with multiple intermolecular interactions, resulting in thermal stability above 300 °C. They exhibit a high intrinsic emission quantum yield (ca. 80 %) due to their asymmetrical and low-vibrational coordination structures around Eu(III) ions. Furthermore, the characteristic alternative orientation of substituents also contributes to the dramatically high ligand-to-metal energy transfer efficiencies of up to 80 % in the solid state.

Luminescent Coordination Glass: Remarkable Morphological Strategy for Assembled Eu(III) Complexes

Syntheses of novel luminescent Eu(III) coordination glasses 1 ([Eu(hfa)3(o-dpeb)]2), 2 ([Eu(hfa)3(m-dpeb)]3), and 3 ([Eu(hfa)3(p-dpeb)]n) are reported. They are composed of Eu(III) ions, hexafluoroacetylacetonato (hfa) ligands, and unique bent-angled phosphine oxide (o-, m-, p-dpeb) ligands with ethynyl groups. Their coordination structures and glass formability are dependent on the regiochemistry of substitution in regard to the internal benzene core. Single-crystal X-ray analyses and DFT calculation reveals dinuclear, trinuclear, and polymer structures for Eu(III) coordination glasses 1, 2, and 3, respectively. Those compounds show characteristic glass-transition (Tg = 25-96 °C) and strong luminescence properties (ΦLn = 72-94%).

Triboluminescence of Lanthanide Coordination Polymers

Triboluminescence (TL) and photoluminescence (PL) of novel lanthanide (Ln(III)) coordination polymers [Ln(hfa)3(dpf)] n (dpf: 2,5-bis(diphenylphosphoryl)furan, Ln=Tb, Gd, Eu) are reported. The coordination polymers exhibited bright TL due to the face-to-face arrangement of substituents between single polymer chains. The observation of TL in a series of Eu(III) coordination polymers and a Gd(III) compound indicated that both hfa ligands and Ln(III) ions were excited under grinding. Significant PL/TL spectral differences in [Tb,Eu(hfa)3(dpf)] n due to distinct excitation processes upon grinding and UV irradiation were observed for the first time.

Luminescent Lanthanide-Mixed Coordination Polymers for Tunable Temperature-Sensitivity

The control of energy transfer efficiency in lanthanide [Ln(III)]-mixed coordination polymers is reported. The coordination polymers [Tb,Eu(hfa)3(dpbp)] n are composed of Tb(III) ions, Eu(III) ions, hfa ligands, and bidentate phosphine oxide ligands [dpbp: 4,4′-bis(diphenylphosphoryl)biphenyl]. The emission colors were controlled by varying the mixture ratio of Tb(III) and Eu(III) ions (Tb/Eu = 1–1000). The obtained compounds were characterized by XRD, emission spectra, and emission lifetime measurements. Temperature-dependent emission color change from green, yellow, orange, to red was observed, and spectroscopic features were discussed on the basis of energy transfer efficiency in the solid state.

Luminescent Lanthanide Coordination Zippers with Dense-Packed Structures for High Energy Transfer Efficiencies

Novel Eu(III) coordination polymers [Eu(hfa)3(dpt)] n [dpt: 2,5-bis(diphenylphosphoryl)thiophene] and [Eu(hfa)3(dpedot)] n [dpedot: 3,4-bis(diphenylphosphoryl)ethylenedioxythiophene] were designed for dense structures with high energy transfer efficiency. The zig-zag orientation of single polymer chains induced the formation of dense-packed coordination structures with multiple inter-molecular hydrogen bonds. These polymers exhibited high intrinsic emission quantum yields (~80%) due to their asymmetrical and low-vibrational coordination structures. The significant energy transfer efficiencies of up to 80% were also achieved.

Amorphous Formability and Temperature-Sensitive Luminescence of Lanthanide Coordination Glasses

Glass-transition properties and temperature-sensitive luminescence of lanthanide (Ln(III)) coordination compounds are demonstrated. The amorphous formability was systematically provided by introducing bent-angled phosphine oxide ligands based on thienyl, naphthyl, and phenyl cores with ethynyl groups. Glass transition points were clearly identified for all Ln(III) coordination compounds from 65 to 87 °C. The Tb(III)/Eu(III) mixed coordination glass also exhibited temperature-dependent emission profiles from green, yellow, orange, to red in the range of 100–400 K.

Luminescent Lanthanide Coordination Glasses

Construction of luminescent Eu(III) coordination glasses [Eu(hfa)3(o-dpeb)]2, [Eu(hfa)3(m-dpeb)]3, and [Eu(hfa)3(p-dpeb)] n (o-, m-, p-dpeb: 1,2-, 1,3-, 1,4-bis(diphenylphosphorylethynyl)benzene) are reported. The coordination structures and glass formability were dependent on the regiochemistry of substitution in regard to the internal phenylene core. Single-crystal X-ray analyses and DFT calculations revealed dimer, trimer, and polymer structures of Eu(III) coordination glasses. All of these compounds exhibited glass transition temperature in the range of 25–96 °C, and strong luminescence was also observed with intrinsic emission quantum yields above 70%.