(E)-Stilbene, (trans-stilbene), is an organic compound with the formula (C6H5CH)2. Classified as a diarylethene, it features a central ethene double bond substituted with phenyl groups on each carbon atoms of the double bond. The name stilbene is derived from the Greek word stilbos, which means shining. It is a white solid that dissolves in organic solvents.
Stilbene exists as two possible stereoisomers. One is trans-1,2-diphenylethylene, called (E)-stilbene or trans-stilbene. The second is cis-1,2-diphenylethylene, called (Z)-stilbene or cis-stilbene, and is sterically hindered and less stable because the steric interactions force the aromatic rings out-of-plane and prevent conjugation. (Z)-Stilbene has a melting point of 5–6 °C (41–43 °F), while (E)-stilbene melts around 125 °C (257 °F), illustrating the two compounds are quite different in their physical properties.
Many syntheses have been developed. One popular route entails reduction of benzoin using zinc.
Stilbene undergoes reactions typical of alkenes, being susceptible to bromination, epoxidation, and cycloaddition. Upon UV irradiation it converts to cis-stilbene, a classic example of a photochemical reaction involving trans-cis isomerization.
Stilbene itself is of little value but serves as a precursor to other derivatives used as dyes, optical brighteners, phosphors, and scintillators. Stilbene is one of the gain mediums used in dye lasers.
The stilbenoids are naturally occurring stilbene derivatives. Examples include resveratrol and its cousin, pterostilbene. The stilbestrols, which are structurally but not synthetically related to E-stilbene, exhibit estrogenic activity. Members of this group include diethylstilbestrol, fosfestrol, and dienestrol.
Table 1. Vapor pressures