Device parameter to evaluate exciton energy transfer in organic whispering-gallery-mode microresonators and its dependence on the amplified spontaneous emission threshold.

Exciton energy transfer in organic whispering-gallery-mode (WGM) resonators and its effect on the amplified spontaneous emission (ASE) threshold have been investigated using the stilbene-based energy donor 4,4'-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) and the coumarin-based energy acceptor 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl)quinolizino[9,9a,1gh]coumarin (C545T). Using the stacked-layer structure of BSB-Cz/C545T/BSB-Cz, we fabricated bowl-shaped microresonators on silica microspheres with a total thickness of 250 nm fixing the thickness of the C545T layer to 1 nm. The ASE threshold depended on the thicknesses of the top and bottom BSB-Cz layers, which affect the magnitude of the energy transfer. To assess the relationship between the ASE threshold and energy transfer, we developed a device parameter to evaluate the magnitude of the energy transfer by formulating the rate equations. We found that ASE easily occurs under the condition that the C545T molecules become unable to accept energy from the BSB-Cz excitons owing to the high exciton density of C545T, and that the ASE threshold decreases with decreasing device parameter. The device parameter is useful for optimizing microresonator structures in multi-component organic WGM resonators that utilize energy transfer.

Chiral metal down to 4.2 K - a BDH-TTP radical-cation salt with spiroboronate anion B(2-chloromandelate)2.

We report the first example of a chiral BDH-TTP radical-cation salt. Chirality is induced in the structure via the use of a chiral spiroboronate anion where three stereocentres are present, one on each chiral ligand and one on the boron centre. Despite starting from a labile racemic mixture of BS and BR enantiomers, only one enantiomer is present in the crystal lattice. The anions pack in a novel double anion layer which is the thickest anion layer found in a BDH-TTP salt. This material is chiral and shows metallic behaviour down to at least 4.2 K.

Enantiopure and racemic radical-cation salts of bis(2'-hydroxylpropylthio)(ethylenedithio)TTF with polyiodide anions.

The chiral TTF-based donor molecule bis(2'-hydroxylpropylthio)(ethylenedithio)tetrathiafulvalene (BHPT-EDT-TTF) has produced enantiopure R,R and S,S radical-cation salts with polyiodide anions I3- and I82-. Enantiomorphic 6 : 6 donor : I3 phases grown from either the R,R or S,S donor are semiconducting with similar activation energies of 0.24-0.30 eV and 0.22-0.23 eV, respectively, and contain three unique face-to-face donor pairs whose relative orientation is determined by side chain conformations and hydrogen bonding. Racemic material under the same conditions gave an insulating centrosymmetric phase with R,R and S,S donor cations in a face-to-face pair partnered with an octaiodide dianion, and with a ca. 3 : 1 disorder between the enantiomers. Enantiopure BHPT-EDT-TTF yielded two further insulating crystalline phases of composition 2 : 2 with triiodide and 2 : 1 with octaiodide.

Development of an optical time-resolved measurement system under high-pressure and low-temperature with a piston-cylinder pressure cell.

To perform the femtosecond pump-probe spectroscopy under high pressure and low temperature, we constructed a measurement system with a piston cylinder type pressure cell installing an optical fiber bundle. The applied pressure was achieved to 6 kbar and the cell was cooled down to 15 K. Several demonstrations revealed that broadening and change of polarization of pulse (duration of ∼120 fs) owing to the dispersions in the fiber bundle are much small indicating that those have little influence on the measurement of carrier relaxation dynamics. In the measurements of κ-(BEDT-TTF)2Cu(NCS)2 under 1.3 kbar at 43 K, we have successfully detected the polarization anisotropy of the carrier relaxation dynamics and estimated the decay time in the same way as the normal measurement.

Enantiopure and racemic radical-cation salts of B(malate)2(-) anions with BEDT-TTF.

We have synthesized the first examples of radical-cation salts of BEDT-TTF with chiral borate anions, [B(malate)2](-), prepared from either enantiopure or racemic bidentate malate ligands. In the former case only one of two diastereoisomers of the borate anion is incorporated, while for the hydrated racemic salt one racemic pair of borate anions containing a R and a S malate ligand is incorporated. Their conducting and magnetic properties are reported. The tight-binding band calculation indicates that the chiral salt has an effective half-filled flat band, which is likely to be caused by the chiral structural feature.

Radical-cation salts of BEDT-TTF with lithium tris(oxalato)metallate(III).

The first radical-cation salts in the extensive family (BEDT-TTF)x[(A)M(C2O4)3]·Guest containing lithium as the counter cation have been synthesized and characterised.

Structures and properties of a BEDT-TTF-based organic charge transfer salt and the zwitterion of ferrocenesulfonate.

The structure and properties of a new semiconducting BEDT-TTF-based charge-transfer salt containing the ferrocenesulfonate (Fc-SO3(-)) anion, α-(BEDT-TTF)2Fc-SO3·2.5H2O, are described. The structure and magnetic properties of a zwitterion of ferrocenesulfonate, Fc(+)-SO3(-), are also reported.

Structures of the reaction products of the AZADO radical with TCNQF4 or thiourea.

While an addition product was formed by the reaction of AZADO (2-azaadamantane N-oxyl) with TCNQF4 (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane), the reaction of AZADO with thiourea provided an inclusion compound, in which AZADO molecules are incorporated in cylindrical channels formed by thiourea molecules.

New BDH-TTP/[M(III)(C5O5)3]3- (M = Fe, Ga) isostructural molecular metals.

Two new isostructural molecular metals-(BDH-TTP)(6)[M(III)(C(5)O(5))(3)]·CH(2)Cl(2) (BDH-TTP = 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene, where M = Fe (1) and Ga (2))-have been prepared and fully characterized. Compound 1 is a molecular conductor showing paramagnetic behavior, which is due to the presence of isolated [Fe(C(5)O(5))(3)](3-) complexes with high-spin S = (5)/(2) Fe(III) metal ions. The conductivity originates from the BDH-TTP organic donors arranged in a κ-type molecular packing. At 4 kbar, compound 1 behaves as a metal down to ∼100 K, showing high conductivity (∼10 S cm(-1)) at room temperature. When applying a pressure higher than 7 kbar, the metal-insulator (M-I) transition is suppressed and the compound retains the metallic state down to low temperatures (2 K). For 1, ESR signals have been interpreted as being caused by the fine structure splitting of the high-spin (S = 5/2) state of Fe(III) in the distorted octahedral crystal field from the ligands. At 4 kbar, the isostructural compound 2 behaves as a metal down to ∼100 K, although it is noteworthy that the M-I transition is not suppressed, even at pressures of 15 kbar. For 2, only the signal assigned to delocalized π-electrons has been observed in the ESR measurements.

Uniaxial strain orientation dependence of superconducting transition temperature (Tc) and critical superconducting pressure (Pc) in ß-(BDA-TTP)2I3.

Dependence of the superconducting transition temperature (T(c)) and critial superconducting pressure (P(c)) of the pressure-induced superconductor ß-(BDA-TTP)(2)I(3) [BDA-TTP = 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene] on the orientation of uniaxial strain has been investigated. On the basis of the overlap between the upper and lower bands in the energy dispersion curve, the pressure orientation is thought to change the half-filled band to the quarter-filled one. The observed variations in T(c) and P(c) are explained by considering the degree of application of the pressure and the degree of contribution of the effective electronic correlation at uniaxial strains with different orientations parallel to the conducting donor layer.

Spin-carrying benzoquinone derivatives.

Several 1,4-benzoquinone derivatives carrying oxy-TEMPO radical(s) at the 2-position or 2,5-positions were found to give black crystals by recrystallization from pale yellow solutions and it was revealed from their crystal structures that unusual single-component CT complexes were formed, in which a nitroxide moiety plays the roll of a donor part and a 1,4-benzoquinone group of the same molecule works as an acceptor part, respectively. On the contrary, no CT formation was found for the derivatives carrying oxy-TEMPO radicals at 2,6-positions and one of the TEMPO groups contributes to a CT formation in a 1,4-benzoquinone derivative carrying amino-TEMPO radicals at 2,5-positions derived from fluoranil, while the other one has a close oxygen-to-oxygen contact with another neighboring molecule to give a very large exchange coupling of J/k(B) = -154 K.

Molecular complexes based on tetrathiafulvalene and dialkylviologens.

Three kinds of molecular complexes based on tetrathiafulvalene (TTF) and dialkylviologens were prepared and their crystal structures elucidated. While TTF-dimethylviologen complex forms a mixed stack arrangement of donors and acceptors in its crystal structure, TTF donors aggregate with long alkyl groups by CH/pi and/or van der Waals interactions in a couple of TTF-heptylviologen complexes.

Azobenzene derivatives carrying a nitroxide radical.

Several trans-azobenzene derivatives carrying a nitroxide (aminoxyl) radical (2a, 6a-12a) were prepared, and their photoisomerization reactions to the corresponding cis-isomers were investigated. Although no fruitful results could be obtained for the photoisomerizations of the derivatives with para-subsituents (9a-12a), the unsubstututed derivatives at the para-position (2a, 6a, 7a, 8a) were found to show photoisomerizations by irradiation to give the corresponding cis-isomers (2b, 6b, 7b, 8b), being isolated as relatively stable solid materials, and the change of the intermolecular magnetic interactions was apparently observed by the structural change for each photochromic couple.

Pressure effect on bulk weak ferromagnets: (BDH-TTP)[M(isoq)2(NCS)4] (M = Cr(III), Fe(III); isoq = Isoquinoline).

The pressure dependence of the magnetic properties of weak ferromagnets (BDH-TTP)[M(isoq)2(NCS)4] [BDH-TTP = 2,5-bis(1',3'-dithiolan-2'-ylidene)-1,3,4,6-tetrathiapentalene; M = Cr, Fe; isoq = isoquinoline] is discussed. These salts form two-dimensional magnetic sheets, where ferrimagnetic chains of donor cation radical (S = 1/2) and anion [S = 3/2 (Cr), 5/2 (Fe)] are antiferromagnetically connected by weak donor-donor and anion-anion interchain S...S contacts. Under ambient pressure, both the Cr and Fe salts undergo a weak ferromagnetic transition at Tc = 7.6 K, below which a spontaneous magnetization emerges along the direction perpendicular to the sheets. The application of the pressure elevates the transition temperatures up to 16.6 and 11.6 K at 9 kbar for M = Cr and Fe, respectively. As the pressure increases, the remanent magnetization M(r) decreases, whose pressure dependence for the Cr salt is larger than that for the Fe salt. This difference indicates that the spin-canting angle of the Cr salt is reduced because of the increase of antiferromagnetic interaction by applied pressure, in contrast to the Fe salt, where single-ion anisotropy contributes less. The quantitative analysis of the magnetization curves of the Cr salt using the mean-field approximation reveals that the intermolecular exchange interaction increases as the pressure increases, among which the interchain anion-anion interaction has the highest pressure sensitivity. This result is consistent with the temperature dependence of the crystal structure showing that the thermal contraction in the distances of interchain anion-anion S...S contacts is the most remarkable in intrachain S...S contacts. The large pressure dependence of the transition temperature of these salts is therefore explained as a result of the fact that the interchain interactions, the anion-anion interaction in particular, are strengthened by applied pressure.

Pressure effect on the electrical conductivity and superconductivity of beta-(BDA-TTP)2I3.

The pressure-induced electrical conductivity properties of beta-(BDA-TTP)2I3 have been investigated; the salt exhibits a dramatic change in the conductivity behaviour above ca. 10 kbar and undergoes a superconducting transition with an onset near 10 K.

Azobenzene derivatives with a long alkyl chain and aminoxyls.

A trans-azobenzene derivative with a long alkyl chain and a TEMPO radical showed photo-induced isomerization to become the corresponding cis-isomer with a significant change of its intermolecular magnetic interaction from a weak ferromagnetic one based on the CW model to a relatively strong antiferromagnetic one based on the ST model with the J-value of 36.7 K.

Superstructures of donor packing arrangements in a series of molecular charge transfer salts.

Three conducting BEDT-TTF charge-transfer salts with tris(oxalato)metallate anions have unit cells containing both[small alpha] and [small beta][double prime] donor packing motifs.

N-salicylideneamine derivatives with TEMPO substituents.

Three N-salicylideneamine derivatives bearing TEMPO (2,2,6,6-tetra- methyl-1-piperidinyloxy) substituents were prepared in order to study their structure and property relationships and to investigate the possibilities of the existence of heat and/or light responsive magnetic properties. Curie-Weiss behavior with weak ferromagnetic intermolecular spin-spin interactions was observed in one of the radicals, while antiferromagnetic interactions were predominant for the other radicals and the structure-property relationships were investigated for the radical compounds from their crystal structures obtained by X-ray analyses. Preliminary results of the examination of their responses towards light and heat are also described.

A new organic superconductor, beta-(BDA-TTP)2GaCl4 [BDA-TTP = 2,5-(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene].

The preparation, crystal structure and physical properties of beta-(BDA-TTP)2GaCl4 has been investigated; the salt exhibits superconductivity at 3.1 K (onset) under a hydrostatic pressure of 7.6 kbar.