The comparison of different stereoisomeric organic compounds
under
high pressure has been less investigated. Here, we chose different
stereochemical configurations of cis/trans-stilbene to study the luminescence
properties, polymerization reaction, and structural changes at 0–20
GPa by spectroscopy and XRD. No fluorescence enhancement occurred
in cis-stilbene due to π–π stacking. At 16 GPa,
the IR, UV–vis, and sample color changes show that it undergoes
an irreversible polymerization, that C(sp2)–H changes
to C(sp2 + sp3)–H. However, trans-stilbene
undergoes fluorescence enhancement at 0–4 GPa due to the reduction
of the torsion angle of the benzene ring and the CC bond leading
to the formation of rigid planar molecules, which is further confirmed
by the IR and XRD results. At 8 GPa, the new peaks in UV–vis
and XRD results show the formation of new substances by structural
change. However, the structure of trans-stilbene is more stable, which
leads to the return to the raw state after releasing the pressure,
and a reversible transformation occurs at high pressure. The cis-trans
isomerization under high pressure was also briefly investigated by
combining heating and laser irradiation. The cis → trans-stilbene
transition can only happen under a fixed-range light irradiation,
and the trans → cis-stilbene transition could not happen even
under irradiation with a 360 nm laser, which may provide a new idea
for synthesizing trans isomers with a higher purity.
Mechanochromic luminescence (MCL) materials have attracted increasing attention due to their versatile functions in many fields. In this work, based on the structure of 3,4-diphenylmaleic anhydride (BPMA, Mei et. al,...
Relaxor ferroelectric crystals of lead magnesium niobate–lead titanate (PMN-xPT) have attracted great attention due to their extraordinary dielectric, piezoelectric, and electromechanical properties. PMN-xPT shows different relaxor behavior and structural phase transitions in a wide temperature and chemical component range. Here, we studied spectroscopy and ferroelectricity of PMN-0.28PT under high pressure. The appearance of a new Raman band and the sudden redshift of UV-vis absorption edge imply a structural phase transition at about 8 GPa. More importantly, the ferroelectricity of the sample is suppressed above a pressure of 5 GPa, and there is no ferroelectricity under further compression. We suggest that the disappearance of ferroelectricity may be related to the polar nanoregions being suppressed by pressure. Our observations of ferroelectricity disappearance above 5 GPa indicate the B-site cation rearrangement in the several nanometers region.
Organic solar cells have become an important development direction in solar cell materials because of their low cost, light weight, and good flexibility.
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