We
report syntheses, crystal and electronic structures, and characterization
of three new hybrid organic–inorganic halides (R)ZnBr
3
(DMSO), (R)
2
CdBr
4
·DMSO, and (R)CdI
3
(DMSO) (where (R) = C
6
(CH
3
)
5
CH
2
N(CH
3
)
3
, and DMSO = dimethyl
sulfoxide). The compounds can be conveniently prepared as single crystals
and bulk polycrystalline powders using a DMSO–methanol solvent
system. On the basis of the single-crystal X-ray diffraction results
carried out at room temperature and 100 K, all compounds have zero-dimensional
(0D) crystal structures featuring alternating layers of bulky organic
cations and molecular inorganic anions based on a tetrahedral coordination
around group 12 metal cations. The presence of discrete molecular
building blocks in the 0D structures results in localized charges
and tunable room-temperature light emission, including white light
for (R)ZnBr
3
(DMSO), bluish-white light for (R)
2
CdBr
4
·DMSO, and green for (R)CdI
3
(DMSO).
The highest photoluminescence quantum yield (PLQY) value of 3.07%
was measured for (R)ZnBr
3
(DMSO), which emits cold white
light based on the calculated correlated color temperature (CCT) of
11,044 K. All compounds exhibit fast photoluminescence lifetimes on
the timescale of tens of nanoseconds, consistent with the fast luminescence
decay observed in π-conjugated organic molecules. Temperature
dependence photoluminescence study showed the appearance of additional
peaks around 550 nm, resulting from the organic salt emission. Density
functional theory calculations show that the incorporation of both
the low-gap aromatic molecule R and the relatively electropositive
Zn and Cd metals can lead to exciton localization at the aromatic
molecular cations, which act as luminescence centers.
We investigated by means of optical microscopy (OM) the spatiotemporal features of the thermo-induced spin transition of [Fe(2-pytrz)2{Pd(CN)4}]·3H2O (1) (2-pytrz = 4-(2-pyridyl)-1,2,4,4H-triazole) single crystals having two different shapes (triangle and rectangle). While magnetic and calorimetric measurements, performed on a polycrystalline material, showed the respective average heating and cooling transition temperatures of (Tdown1/2 ∼ 152 K, Tup1/2 ∼ 154 K) and (Tdown1/2 ∼ 160.0 K, Tup1/2 ∼ 163.5 K), OM studies performed on a unique single crystal revealed significantly different switching temperatures (Tdown1/2 ∼ 152 K and Tup1/2 ∼ 162 K). OM investigations showed an interface spreading over all crystals during the spin transition. Thanks to the color contrast between the low-spin (LS) and the high-spin (HS) states, we have been able to follow the real time dynamics of the spin transition between these two spin states, as well as access the thermal hysteresis loop of each single crystal. After image processing, the HS-LS interface's velocity was carefully estimated in the ranges [4.4-8.5] μm s-1 and [2.5-5.5] μm s-1 on cooling and heating, respectively. In addition, we found that the velocity of the interface is shape-dependent, and accelerates nearby the crystal's borders. Interestingly, we observed that during the propagation process, the interface optimizes its shape so as to minimize the excess of elastic energy arising from the lattice parameter misfit between the LS and HS phases. All of these original experimental results are well reproduced using a spatiotemporal model based on the description of the spin-crossover problem as a reaction diffusion phenomenon.
This study does not seem to confirm the described association of anti-P antibodies with neuropsychiatric manifestations of SLE. However, it supports the anti-P antibody association with arthritis and disease activity as well as the presence of aCL. Based on our study and other related studies, we propose that, akin to anti-Sm and anti-dsDNA, anti-P antibodies detected by one agreed method may be considered for inclusion as a criterion for the classification of SLE.
We have investigated
by optical microscopy the thermal spin transition
of a single crystal of the spin-crossover compound [{Fe(NCSe)(py)2}2(m-bpypz)] under various shining
intensities, far from the light-induced spin-state trapping region.
We found evidence of photoheating on the thermally induced hysteretic
response of the crystal, leading to the control of the transition
temperature and the hysteresis width as a function of the light intensity.
The inspections of the spatiotemporal behaviors of the spin-crossover
transition, on heating and cooling, have also evidenced a significant
dependence of the propagation speed of the high-spin–low-spin
interface on the intensity of light. In particular, for strong shining
intensities, a slowing of the interface speed at the transition is
obtained, and an unprecedented dynamical two-step-like transition
was observed in the thermal hysteresis. These results are analyzed
theoretically using a spatiotemporal approach based on reaction–diffusion
equations including the spin-state propagation and the heat transfer
between the crystal and the thermal bath. The obtained results are
in good agreement with experimental observations and lead to identification
of the key factors governing the interface velocity and the thermal
hysteresis behaviors under the light excitation in spin-crossover
materials.
We have investigated by means of optical microscopy and magnetic measurements the first-order thermal spin transition of the [{Fe(NCSe)(py)2}2(m-bpypz)] spin-crossover compound under various shining intensities, far from the light-induced spin-state trapping region. We found evidence of photo-heating effects on the thermally-induced hysteretic response of this spin-crossover material, thus causing the shift of the thermal hysteresis to lower temperature regions. The experimental results are discussed in terms of the apparent crystal temperature and are analyzed theoretically using two evolution equations of motion, written on the high-spin (HS) fraction and heat balance between the crystal and the thermal bath. A very good qualitative agreement was found between experiment and theory in the stationary regime, explaining the experimental observations well and identifying the key factors governing these photo-thermal effects.
Optical microscopy technique is used to investigate the thermal and the spatio-temporal properties of the spin-crossover single crystal [Fe(2-pytrz) 2 {Pt(CN) 4 }]·3H 2 O, which exhibits a first-order spin transition from a full high-spin (HS) state at high temperature to an intermediate, high-spin low-spin (HS-LS) state, below 153 K, where only one of the two crystallographic Fe(II) centers switches from the HS to HS-LS state. In comparison with crystals undergoing a complete spin transition, the present transformation involves smaller volume changes at the transition, which helps to preserving the crystal’s integrity. By analyzing the spatio-temporal properties of this spin transition, we evidenced a direct correlation between the orientation and shape of HS/HS-LS domain wall with the crystal’s shape. Thanks to the small volume change accompanying this spin transition, the analysis of the experimental data by an anisotropic reaction-diffusion model becomes very relevant and leads to an excellent agreement with the experimental observations.
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