Comparative Study on Properties, Structural Changes, and Isomerization of Cis/Trans-Stilbene under High Pressure

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 C═C 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.